NATS 1880 Notes (Week 1-12) PDF

NATS 1880 LIFE BEYOND EARTH Week 1 Key Questions: Why are we here? - Formation of organic molecules essential to life - Birth of our sun - primary energy source for life - Formation of our planet Are we alone? (do aliens exist?) - Where are they? Do they look like us? Are they friendly?...

NATS 1880 LIFE BEYOND EARTH Week 1 Key Questions: Why are we here? - Formation of organic molecules essential to life - Birth of our sun - primary energy source for life - Formation of our planet Are we alone? (do aliens exist?) - Where are they? Do they look like us? Are they friendly? - Look at our solar system for life of some kind (not large scale or intelligent) like single or multicelled organisms How did life emerge from lifelessness? - How did it happen for the first time? - The only place we do know that has life is Earth Using methods for exploration → find planets - What are they like? Are they habitable? Do they host life? (just b/c it can doesn’t mean it does) Interstellar travel - Can we go there, live with them? How would it be possible? Is there life beyond earth? Depends on who you ask: - philosophers will ask, “does an entire universe needs to be created for one place to have life?” - Sci-fi writers: if there is or if there isn't, both are interesting - Astronomers: wide range of life on earth than can live in extreme conditions, so life in other planets seems likely What are we searching for? Intelligent species vs. microrganisms in the soil Defining life - Simple, complex, or intelligent - Can take on different forms than earth - Definition factors: reproduction, moving and growing, but not entirely accurate/complete b/c fire and crystals take on these characteristics What we think we know: - No macroscopic life - Microbial life is possible - Everything we know about select planets seem habitable but not sure - Capabilities are growing to the search ex. Titan (a moon of saturn) submarine used to explore the methane bodies of water - Starshot: how to send microsatelites to other star systems which are far away (thousands of years away) The search for life is interdisciplinary: Astronomy - Earth is not that special - universal laws of physics seem to apply everywhere ex. Gravity behaving differently - Sun pulls the earth, the earth pulls us - Where gravity repells, it would be hard to understand and study - Hotter gasses move faster, but if it were reversed, would also be hard to understand - Life could have formed somewhere somehow other places - 200 billion trillion stars in the universe and the same amt of planets - On avg, every star has 1.5 planets Planetary Science (environmental and atmospheric science) - How planets form (natural byproduct of how stars form) - How and why planets are different ex. Gas planets, rocky, different atmospheres - Their evolution, how habitable they are Biology - Do you expect life to be rare or common? - If laws of physics are universal, then the laws of biology are too - Physics can be tested but biology is more difficult - See the same molecules from space that are also on earth → extreme conditions where the ingredients of life are common, hinting to chem - Stars are mostly hydrogen, some helium - mostly made out of the same things  - Earth is 4.5 billion years old - No reason to believe life is rare and many reasons to believe that its common Where should we search for life in the Universe? - Place with liquid - water - Habitable range around the sun, so too close water will boil and evaporate, and too far it will freeze - carbon - building block of life - Time - don’t look at newly formed planets or very old b/c they don’t have complex molecules - Heat (sun) - Atmosphere which is protection from radiation in space Ingredients for life - A liquid or solvent ex. Water, methane - Heat – sun - Time to develop complex molecules – don't wanna look at old things bc there is no carbon - Protection – atmosphere to protect from solar flares, UV radiation Evidence for sub-surface water on Mars and several moons (unknown energy, consistent states of water, no atmosphere) - Callisto - Europa - Encedalus - Ganymede Beyond our system - More difficult to look for life on planets farther away - 1 billion can be seen with our technology - Spectral analysis: looking at what a planet looks like in all wavelengths of light to see how hot it is, how earth like is it/conducive with high accuracy We have scientific reasons to think that extraterrestrial life is possible, but no confirmed evidence that life exists Could aliens be searching for us? - If life is common enough, shouldn’t there be other species that’s also looking for life outside their planet? - Could they be signalling us? If they know we’re here Direct Communication SETI (search for extraterrestrial intelligence institute) - International collab that actively searches for alien signals – radio telescopes, satellites - Search for civilizations that live beyond earth (intelligent life) - They mostly get radiation Messaging ETs - Targeting possibly habitable planets Should we be contacting ETs? - Pursuit to answer “are we alone?” - Could it result in a peaceful existence or warlike existence? Humanities past does not work in our favor - Could unify earth – see ourselves as one and knowledge exchange from them - If we evolved through violence, who’s to say that they haven’t either and are trying to wipe us out once they locate us How do we study the possibility of life beyond earth? Interdisiplinary - Studying conditions, looking for them on other planets - Actively looking for them on other planets Week 2 The Science of Life in the Universe How we can turn the search for life outside of earth into a science Astrobiology: Brings together geosciences, biology, astrology whos goal is to understand life on our universe and beyond - Use science to understand the conditions under which we expect to find life - Possible characteristics of life beyond earth - Methods for finding life beyond earth Start at the beginning: Understanding the Sky To measure - divide 360 degrees into North, west, east, and south - Altitude is how high you are from the horizon - Azimuth is the movement from north to east etc. Measure apparent size of things in the sky  - Moon, sun and separation between stars - Pinky is 1 degree, fist is 10 degrees, the sun and moon are 0.5 degrees apparent size The Sun - Rises in the east and sets in the west - Path across sky varies with seasons → lower in the sky in winter (20 degrees) so the days are shorter b/c it only has to go up 20 degrees The Moon - Phases → how much you can see (relative to the location of the earth and the sun) - Full moon - it is on the opposite side of the sun - Phase is related to tides - times of day when the water levels are higher (high tide) or lower (low tide) The Stars - At night, they move across the sky - Only appear at night - Constellations (grps of stars) appear at different times of year - Stars rotate around a single point - north star The Planets - Brighter, don’t twinkle (starlight hitting atmosphere and it scattering the light) - Move through the stars while they stay still - Over a few weeks, we see planets move relative to the stars, but we do not see the stars move relative to each other Beginnings of Astronomy - Ancient chinese (5000 yrs) star charts - Babylonian (2500 yrs) eclipse predictions Distances in Astronomy - 3D universe projected on 2D image which is our sky Greeks Attempt to Understand the Universe Thales of Miletus (600 BCE) - Earliest documented case of someone asking “what is the universe made of?” - Felt universe could be understood, sun moved across the sky for a reason that needed to be understood Model of the Universe - Goal is to create a model that encompasses observations like: the sky changes daily and monthly, feels like were fixed in position - Model can be a lens to view the data Flat Earth under Dome-like Sky - Tried to advance geometry, causing them to abandon the flat earth theory b/c it doesn’t explain the movement of the objects in the sky - Spheres come into the picture Celestial Sphere - Earth is a sphere, then there is a larger sphere surrounding the earth and it rotates around the earth, which explains the motions of the stars - Moved away from this model b/c of the detailed behavior of the planets (move differently in respect to the stars) - How can this motion be possible? Geocentric Model 2.0 - Created more spheres → sun, moon, planets have their own celestial sphere, which is differently sized, allowing them to be different distances from the earth (still in Ancient Greece) - Popular at the time of Shakespeare (Elizabethan Era) → starcrossed lovers: to be 2 stars stuck to the inside of the sphere, forever remaining a distance apart (fixed) - Inaccurate b/c stars will not remain forever apart - Poor job of predicting the motion of sun and planets Planetary Motion: More complex, seem to move backwards at time (retrograde motion), brightness changes Ptolemy’s Model - Added more circles - Planets move around the earth on small circles that are turning around larger circles - Did better job at predicting motion in sky - Represents the roots of modern/western science: science that was developed and passed down in eurocentric cultures - Lasted 1500 years Aristarchus (260 BCE) - Suggested that planets orbit the sun and the moon orbits the earth  - Easily explained the retrograde motion of the planet - theyre not actually moving backwards - Inner planets orbit faster than the outer planets, moments where inner catches up to and passes the outer planet along orbit, when this happens, outer planet appears to move backwards on sky Heliocentric Model - Ppl. rejected it the time b/c they believed if the earth revolved around the sun, then the positions of stars should change over the course of the year - should be times we’re slightly closer or farther from the star - Philosophical reasons for rejection: earth being the centre of the universe made a lot of sense b/c earth is special due to religious and societal beliefs Life Beyond Earth in the Age of Ptolemy Model Dependant - Opinions depended on who you asked and what model you subscribed to - Ancient Greeks were open to the possibility that other worlds exist - ours consisted of the earth and celestial spheres - Whatever the universe was made of was infinite - Debate with ET research was heavily intertwined with religion b/c if there is ET life, then there are other worlds that are possible - There was significant debate, with some thinking that ET life existed and others arguing against it - No insistence that we were the only world, led to 2 emerging philosophies: Atomists - World consists of infinite number of fire, water, air, earth atoms - Earth and heavens were created by random motions of these atoms - come together and form our world - Since atoms are infinite, other worlds are simply implied - Ours isnt special in the grand scheme - Epicurus Aristotelians - Fire, water, air, earth were only on Earth and everything else was made of some 5th element or ether you couldn’t form things out of - Each of the 4 elements has its own natural motion in place - earth moves towards the centre of the universe (why its in the centre) - Fire moves away from the centre - why the sun is in the sky - The world is unique, there cannot be several worlds  - His work became associated with religions at the time and atonomists were associated with atheists Copernican Revolution (Western Europe) - 1st millennium, Islamic scholars developed algebra, sought knowledge about math and astronomy from early Greek works - Collaborated with Indian and Chinese scholars - Baghdad turned into the centre for science and philosophy - Byzantine capital was conquered in 1453 and scholars headed west - European renaissance occurred then the shift to west occurred - Copernicus revived the Heliocentric model with the help of math - led to natural relationships between the orbital periods and distances of the planets - Omitted Ptolemy’s circles - Did not improve the prediction of where the stars would be during the night and never gave an explanation of why the locations of stars change - Debate of Copernican Model vs. Ptolemy’s Model - Ppl. would design experiments to back their standings Tycho Brahe - Improved observations (naked eye) of the planets would differentiate these models - Did NOT measure parallax - earth is the thing thats fixed (Ptolemy) or stars are so far away we cannot pick out the motion with our eyes - Did NOT help distinguish between 2 models Stellar Parallax: the slight back and forth motion shifting of a star’s position relative to more distant stars that occurs over the course of a year Kepler (Physicist) Non-Circular Reasoning - After years of trying to fit Brahe’s data (planets move into circular orbits, diverge theories) maybe planets don't move in perfect circular orbits - Supported Heliocentric model → Kepler’s publication didn’t explain the motion being felt for the earth moving and not observing stellar parallax - The breakthrough that allowed Kepler to discover the laws of planetary motion was his realization that planetary orbits are elliptical rather than circular Kepler’s 3 Laws - Laws of Orbital dynamics that explain all of Brahe’s observations  1. Orbit of each planet about the sun is an ellipse (not perfect circle) with the sun at 1 focus 2. Planet moves faster in its orbit when closer to the sun (perihelion) and slower farther away from the sun (aphelion) → sweeps out equal area in equal time 3. More distant planets orbit the sun at slower average speeds; Period squared = axis cubed Maria Cunitz - Published in 1650 where she corrected errors in Kepler’s work, simplified derivations and presentations of laws - Published in Latin and German which allowed it to be shared with the world Galileo - Any object on the ball will keep rolling with the ball unless another force acts upon it → we will keep moving with the earth (rolling ball experiments) - Broke notion that cosmos had to be perfect → Observed sunspots on the sun, valleys on the moon - Showed when viewing milky way, if you point your telescope in areas where it is dark, you can see them still though they are far away - Observed moons of jupiter, and venus had phases like our moon does Physics Behind the Heliocentric Model Issac Newton - Difficult to answer why we should trust the Heliocentric model b/c there weren't tools that existed at that time - Invented calculus → needed to explain Kepler’s Law - From calculus came Newton’s laws of motion and gravitation: Newton’s 3 Laws 1. A force is needed to alter an objects velocity (velocity vs. speed) - velocity includes directional motion ex. Car going 100km/h North 2. Force acting on object, mass of object, and exceleration it experiences are related by this equation: Force = mass x acceleration or acceleration = force/mass - Stronger force = higher acceleration 3. For every force there is an equal opposite reaction force - Both on skates, one pushes the other and both move away from each other Universal Law of Gravitation - Every mass attracts every other mass through the force called gravity - The strength of the force attracting any 2 objects is directly proportional to product of their masses → higher mass = stronger gravitational pull - The strength of the force attracting any 2 objects is inversely proportional to distance between them → close, gravitational pull is stronger - Accepted over other theories bc it explained Galileo’s ovserations, Kepler’s laws of planetary motion, predict the motion of comets (Haliey’s comet used Newton’s law to predict the comet’s return years later) - According to Newton’s universal law of gravitation, if you triple the distance between 2 objects, then the gravitational force between them decreases by a factor of 9 Problems with Law of Gravitation - Orbit of mercury does precession → does not return to the same spot every time it orbits the sun - Maybe another planet we haven't observed? - Newton didnt like the idea of mysterious gravity force, mechanism to fit the theory How did the Copernican revolution alter the ancient debate on ET life? - Model inderectely implied that other worlds are entirely possible → earth is not the centre of the universe - Mindset leads to people seeing life in the wrong places → galileo thought the moon had an atmosphere, Kepler suggested the moon was inhabited, Herschel (discovered Uranus) assumed all planets were inhabited, Lowel (1800s) believed to see artificial canals on Mars from martians - UFO sightings in 1900s - Careful that we’re seeing it b/c its actually there, not b/c we want to The Nature of Modern Science Scientific Method 1. Make observations 2. Ask a question 3. Suggest a hypothesis 4. Make a perdiction 5. Perform an experiment to test hypothesis → if test supports, make additional observations and test them → if test doesn’t support hypothesis, revise hypothesis or make a new one  - Idealization, not everything can be observed, but can make predictions - Observations of nature are generalized - Ex. extinction of dinosaurs - cannot directly observe history but we have fossils → massive impact theory: find crater in Mexico providing evidence that this theory is correct Hallmarks of Science - Instead of perfect scientific method, can try to define scientific thinking - Science seeks explanations for observed phenomenon that rely solely on natural causes - Science progresses through the creation and testing of models of nature that explain the observations as simply as possible - Scientific model makes testable predictions about natural phenomena that would force us to revise or abandon if predictions do not agree with observations Simplicity: Occam’s Razor (Science progresses through the creation and testing of models of nature that explain the observations as simply as possible) - When faced with 2 equally good hypotheses, always choose the simpler Verifiable Observation (Scientific model makes testable predictions about natural phenomena that would force us to revise or abandon if predictions do not agree with observations) - Personal testimony cannot be verified ex. UFO sighting - Something that can be repeated to be verified Objectivity - It is good to think inside the box to test the box for weaknesses, It is good to think outside the box to build new boxes - Despite these hallmarks, objectivity will be involved with humans which leads to bias - Cultural bias: religion vs. science - Individual bias: artificial canals on Mars - Community bias: einstein’s theory of relativity Scientific Theory Theory: Model that is powerful, simple, and makes predictions that survive repeated and varied testing  - Never be proven beyond a doubt due to possibility of future observations - Might require replacement all together - Ex. Darwin’s Theory of Evolution - Scientific models are used to make specific predictions that can be tested thru observations or experiments - Theory: A broad idea that has been repeatedly tested and verified, giving scientists great confidence that is represents reality Fact of Gravity - When thinks are dropped they fall - Planets orbit the sun Theories of Gravity - Gravity is a property of heavy objects → heavier falls faster but not true b/c its really due to air resistance - Things falling on earth and planets orbiting the sun are due to the universal law of gravitation Theory of Relativity Einstein - Explain the gravity, abandoning the idea of forces all together - All objects exist in 4D space-time - Massive objects curve spacetime → bowling ball in a sheet, things will fall towards ball - Gravity is result of curvature of spacetime - Accurately predict orbit of Mercury, massive objects bend light Theory of Life in Universe - Currently does not exist - Astrobiology will help sort this out Week 3 Universal Context of Life Earth - 150 million km from the sun → 1 astronomical unit (au) - Only known place to host life Rocky surfaces: earth, mercury, venus, and mars Gas surfaces: jupiter, uranus, neptune, saturn Logarithmic scale: factors of 10 are equally spaced out - If the universe were shrunk by a factor of 1.4 billion, the sun’s diameter is a metre and humans would be the size of microbes Oort cloud - Comets bound to the sun - Past neptune, the farthest most planet - Farthest spacecraft Voyager 1 went 100 AU - Where sun’s gravitational pull gets weak (100 AU) Sun’s Nearest Neighbor - 99% of universe’s mass is the sun - Triple star system: Alpha centauri A, B, C - Alpha centauri C has 2 known planets and 1 is potentially habitable - 40 trillion km away Light Years - Unit of distance generated from the fact that light has a finite speed: 300 million m/s - Light travels differently through gas and liquid - How far can light travel in a year? 10 trillion kms - 1 light year = 9.46 trillion kms - 27 000 lightyears from the centre of the galaxy Lookback Time - It takes time for light to travel large distances → when you are looking at something very far you are seeing it in the past - 131 stars, white dwarfs (dead stars), brown dwarfs (failed stars) within 20 ligthyears of the sun → only 22 visible with eye The Milky Way Galaxy - A giant collection of more than 100 billion stars - Gaia satellite allows astronomers to map out the milky way - See stars in a range of colors, their positions, can measure their velocity - 50% are part of a binary system, can move together - Globular clusters: old stars and others clumped together Parsecs - Unit of distance - Any star 1 parsec away will have a parallax of 1/3600th of a degree - 1 pc = 3 light years The Local Group - Small collection of galaxies that are all gravitationally bound (we are part) - Andromeda - comparable to Milky way - Triangulum - smaller than Andromeda - 80 dwarf galaxies Virgo Cluster: galaxy cluster - Virgo supercluster - we are gravitationally bound Laniakea - Virgo supercluter is part of this - Great attractor - connected but not bound - We formed in some related manner but futures are not entwined - All part of the Cosmic Web What is the Universe Made of? Matter - Subatomic particles → quarks, leptons etc. - Atoms → protons (+) neutrons in nucleus, electrons (-) around nucleus - Atoms often neutrally charged if all atoms are the same - Quantum probability cloud: tells us where the electrons are likely to be - Possible to gain or lose electron, leading to charge Elements - # of protons in nucleus (atomic number) tells you what element is - Ex. 1 proton is hydrogen  - Electrons of elements are only allowed to move in specific orbitals - path of movement → closest to nucleus is ground state, next is the first excited state, then second excited state etc. - Farther away you go from the nucleus, the higher the energy - Cannot occupy a space in between orbitals bc orbitals have specific energies - If it wants to go to higher orbitals, it needs extra energy → gets energy by absorbing photons (light) - Can only absorb photons of specific energy and wavelength that correspond to difference between orbitals Isotopes - Atoms that have the same # of protons but different # of electrons - Neutral hydrogen has 1 proton and 1 electron, but if it gains then it is a negative isotope Molecules - Atoms can come together to form molecules (share electrons) - Forms chemical bond - Life is made of carbon elements → organic matter - A tiny nucleus, made of protons and neutrons, surrounded by a cloud of electrons that give the atom its physical size Phases of Matter: Molecules can have different phases ex. Water can be solid, liquid, or gas, then plasma Energy Kinetic energy: energy of motion Radiative energy: energy carried by light – allows light to interact with matter Potential energy: stored energy that can be covnerted into kinetic or radiative energy Subclasses of Energy Mass Energy: mass itself if a form of potential energy → E = mass x c squared (speed of light) Thermal Energy - Type of kinetic energy - Use to describe energy contained in a system that's responsible for its temp - Heating substance increases motion of molecules - Chemical reactions increase motio of molecules Conservation of Energy - Energy cannot be created or destroyed - It can change forms → matter/mass to energy and back - Ex. energy is generated by the sun by the conversion of mass energy to radiative energy How to study matter and energy of things lightyears away? Light - Light is radiative energy that travels through space at a fixed speed and through the universe as an electromagnetic (EM) wave - electromagnetic (EM) wave: waves that are created as a result of vibrations between an electric field and a magnetic field - Aka. oscillating electric and magnetic fields - Any wave’s wavelength is speed/frequency - Since light is fixed speed: speed of light/frequency → red has longer wavelengths, blue has shorter wavelengths and longer frequency, so higher energy - Red light is lower energy Wave-Particle Duality - Collections or packets of energy called Photons - When considering light as made up of individual pieces, each characterized by a particular amount of energy, the pieces are called photons - Photons can exert pressure, scatter, transfer energy Learning from the Light 1. Imaging - Astronomers will take a single picture focusing on a single band of light and focus on that or let in a very specific wavelength 2. spectroscopy - Break all incoming light into full spectrum and measure how much light at each wavelength that object is emitting - Measurement of how bright something is at specific wavelengths - Any dense object ex. Stars, ppl emit light as a continuous spectrum with a characteristic shape → can determine temperature called thermal radiation or black body radiation (infrared) Blackbody Radiation (due to thermal) - Thermal radiation: radiation with a spectrum whose shape depends only on the temp of the emitting object  - Characteristic shape → sharp rise in intensity, then falls as you go even higher - Low wavelength = low emission - sun – 5600 celsius on surface - Can learn about an object from the light that's missing or extra light - Elements want to stay in stable state, warm is less stable Law 1: Hotter objects are brighter Law 2: Hotter objects the peak of the spectrum moves left (to shorter wavelengths) Spectral/Absorbtion Lines - Different stars have different spectra - Peak brightness corresponds to the temp of the stars - Gaps in chart are called spectral lines – occurs if light from hot source passes through cooler gas cloud, then atoms of that could absorbs some light at specific wavelengths, which get absorbs depends on what the could is made of - Spectral lines are unique to each element What if the Source is Moving? Doppler Effect - When moving forward in water, the ripples are closer together in front of you and farther apart behind you - Sound – when source of sound (wave) is coming towards you, the frequency or pitch is higher and lower when moving away - light – any source moving towards you, the light shifts to higher wavelengths - small effect for light bc speed of light is fast - Spectra – if object is moving towards us = bluehshift - If object is moving away from us = redshift - Moving to the side = no shift What does Light from the Universe tell us? Dark Matter - Spectre plays a role in dark matter, how fast stars move - Things farther away from the sun move slower due to gravity - In the galaxy, stellar velocity increases as you move away from the centre and constant in the outer regions - Gravity tells that matter is there - dark matter bc we can’t see Universe is Expanding - Figured out by looking at how fast galaxies are moving away from us as a function of distance - Saw in every direction, galaxies are moving away from us – farther ones are moving faster - The space itself is expanding Week 4 Model for the Universe How did we get from the Birth of the Universe to Life on Earth? Scientific Method: Observations - Universe has a radius of 14 million light years, the same age of the universe - Consists of dark energy → universe is expanding - Galaxies are found in groups, clusters coming together to form cosmic web - Stars orbit within galaxies → ways they orbit, velocities and how far they are from galaxy centres tell us there is some dark matter - Planets orbit stars, planet is host to diverse range of life forms - Cannot directly observe “big bang” but can indirectly observe from behaviour of distant galaxies - Take formalism and make observable predictions – if big bang is correct, what else is true Expanding Universe - Theory of expanding universe implies the universe was smaller - so tiny it was a singularity and born out of massive explosion → Big bang - Universe would be hot and dense as it expands - Raisin cake example: 3 raisins, living on raisin 1 would make the 3rd and farthest raisin move faster away after baking - Raisin is only aware of surface of cake – 2D world - Think of universe as 4D balloon – our 3D represents the surface of the balloon and there is an unseen 4th dimension - Expansion of the universe is the 4D balloon blowing up Predictions - An expanding universe will cool – from hot, dense plasma - Cool enough for protons to form – 1 10,000th of sec after big bang - As it cools more, nuclear fusions occur to create nuclei for elements to form — same as stars  - Neutrons and protons combine to create heavy hydrogen, production of helium Nucleosynthesis - As hot universe cools, helium, hydrogen, lithium grows - Abundances are set in stone - 75% hydrogen, 25% helium, trace quantities of lithium - So dense that photons were absorbed or scattered - lose info about its origin, properties become attributed to scattering event - Estimates of chemical composition of oldest objects, consistent with abundences of stars - 380 thousand years after big bang – universe cooled enough for electrons and nuclei can combine to form atoms - When this happened, universe became less dense and more transparent - radiation can flow freely without being scattered - Should be afterglow of radiation during this time - observed as nearly uniform microwave light in all directions - Overdensities would lead to galaxies forming, underdensities lead to voids (density of microwave light) Big Bang Theory - Predicts an expanding universe - Predicts abundances in elements of early universe - Predicts uniform afterglow from the time of recombination - Why Microwave Light? Why microwave is in afterglow section – entire universe was 3000 degrees, so most photons would be infrared light, expansion stretches light to longer wavelengths How do we get from Hydrogen, Helium, and Lithium to life on Earth? - We can see light after the time of recombination with a good telescope - study universe in detail First few hundred million after Big Bang - the universe will continue to cool until overdensities of gas can collapse due to gravity - very first stars and galaxies form - Stars are powered by nuclear fusions in their cores - creating new elements - Very first supernova - first gen of stars made of hydrogen, helium, huge and bright but didn’t live long - Collapses in on itself and implodes - creates new elements as nuclei collide - Universe becomes poluted with heavy elements - anything with 2 or more protons are considered heavy - Heavy elements are necessary for panet formation, formation of organic molecules (Life)  - Later gen stars are forming from polluted material Universal Enrichment - Galactic recycling occurring in Milky way - chemical composition should be similar to other galaxies - Less pollution in young systems vs. later systems - Raw ingredients for life should be everywhere - Creation of every other element is related to stars – death or merger of stars - We are “star stuff” - every atom in your body is created in the merging or death of stars and billions of years later teams up with other atoms and creates you Molecular Clouds - As galaxies form, atoms are gravitationally attracted to each other, and end up bound as part of molecular cloud - Seeds of star formation - As galaxy gets polluted from death and formation of other stars, so do molecular clouds - Considered to be dense regions of gas in interstellar space - low density in comparison to earth - 99% gas - hydrogen, 9% helium, co2, 1% dust (grains of carbon and soot) that serve as formation site for molecules - As molecule clouds become enriched, organic molecules can form on dust grains which can combine on the surface - Time limit for first lifeforms on universe How did our Solar System Form? Scientific Method: Observations - There are clear patterns of motion - planets orbit the sun in counterclockwise motion - Same direction that sun rotates - Planets have almost circular orbits and rotate in CCW motion too 2 Types of Planets Terrestrial - mercury, venus, earth, mars - Small, close to the sun, made up of metal and rock, few moons and no rings Jovian - jupiter, saturn, uranus, neptune - Large, far from the sun, hydrogen-helium compounds, all rings, many moons Dwarf Planets - Massive enough that their own gravity has made them spherical - Orbit the sun - have NOT cleared their orbit → other astroids around along their orbit, which classifies them as dwarfs Asteroids - Weakly bound rubble piles of metal and rock that orbit the sun - Not massive enough to be spherical, shares orbit with other asteroids - Large collection in asteroid belt between Mars and Jupiter - Some move through our inner solar system, threatening Earth - If other solar systems form in the same way that ours does, its possible that asteroids threaten their systems too, pointing to the abundance or lack of life forms Comets - Similar to asteroids but significant amount of ice - Sometimes pass close by, the ice vaporized into tails - Found father from the sun than asteroids - Found in Oort cloud and Kuiper Belt Oort Cloud - Predicted by tracing backwards the orbits of some comets, revealing long orbital periods - 1000 to 10,000 AU from the sun - Made of Billions of comets, though theoretical prediction Exceptions - Earth and Uranus have a tilted rotation - not perfectly inline to sun - Venus rotation appears to be rotating backwards - Some moons in solar system with backwards/inclined orbits, goes against orderly motion - Earth's Moon: massive but around inner region of planets, which goes against observed properties of small inner and large outer planets Hypothesis 1 Close Encounter Model Buffon (1745) - Suggested that planets form from debris due to comet that collided with Sun - Revised: planets form by blobs of gas pulled from Sun due to passing encounter with star - popular in early 20th century  - both models were incomplete: could not explain the orderly motion of planets, could not explain 2 types of planets, required rare event to create planets (stellar encounter) - Incompatible with idea of life beyond earth → predicts planetary systems are going to be very rare - Predicts life is going to exist only in our solar system Hypothesis 2 The Nebular Theory - Competing model in mid 1700s - Suggests that over 9 billion yrs after big bang, cloud of gas that would become our solar system collapsed - externally triggered by possible passing star - Billions of yrs of pollution led to 2% of H and He to convert to heavy elements - Cloud is made out of cold gas and dust, Slowly rotating - Once collapse starts, laws of gravity ensure it will continue - As size of cloud decreases → force of gravity gets stronger (inverse square law) - Collapse (initially spherically symmetric) flattens out due to heating, spinning, flattening Heating & Spinning - Heating → Conservation of energy - Spinning → Conservation of angular momentum 1. Linear Momentum - Product of object’s mass x velocity - Newton’s Laws: Force is required to change objects momentum - Colliding with object that has high momentum imparts a large force - Conserved quantity - Ex. rolling pool ball (ball A) colliding with stationary pool ball (ball B) will cause Ball A to become motionless and Ball B to move → momentum is transferred - If mass is = then incoming velocity will be equal between 2 balls - If Ball B is larger than Ball A, then velocity will be slower and vice versa 2. Angular Momentum - Related to rotation: mass x size x velocity - Size is how far the object is to the axis of rotation - Large objects will spin slowly, and small will spin quickly - Ex. figure skater with arms out will spin slower and arms in will spin faster due to conservation of angular momentum  Flattening - Direct result of this spinning - Results from collisions of particles in a spinning cloud - clump of gas and dust merges, resulting clump has average velocity of incoming clumps, resulting in the motion of the same direction - Process of forming a star Modifications to Nebular Theory - Protostars are observed with jets of charged particles being emited from their poles resulted from forming magnetic fields - Observed planets with masses and sizes between the Jovian and terrestrial categories - Formation resulted from differences between how long they turn into planets before gas is blown away - Exo joivan planets that bring them in the frost line → migrate after forming Planetary Migration 1. Comets in Oort Cloud will undergo interaction w planets taking energy from them and causing the planet to migrate inwards after losing energy 2. Drag force from gas in disk causing it to slow down and migrate inwards - depend on time it took for planet to form and gas to be kicked out 3. Planet - planet interactions - depends on relative orbits, results in some planet kicked outwards and the other moved inwards Protostar Formation - Centre of disk - While flat disk is forming, the inner most regions of cloud are collapsing inwards - Starts heating up, collisions of molecules creating photons that radiate some energy away - Eventually too dense for photons to escape and collapse is halted, increasing temp - Becomes star when core ignites – 10 million degrees K - Nuclear begins in core - halts collapse of core bc radiation pressure - Now emitting solar wind of charged particles that clears up remaining gas Planetesimals - before clearing, planets form - Small objects that stick together to from planetesimals - seeds to form planet - Material used differs depenign on distance from sun → interior to frost line has rock, metal, gas, and outside frost line also has ice - Hydrogen compound can turn solid, building larger planetesimals in outer regions of solar system  - Planetesimals can accrete gas to form planets - ice allow for larger cores and more gas accretion ex. Jovian - Hyp1 one time preferred over Hyp2 bc Hyp2 originally predicted planets form from rings around a star, which Physists showed not possible - Once Hyp2 expanded to allow for formation of solids that could accrete gas, the complication dissipated, puting Hyp2 in favor Does the Nebular Theory explain observations of our Solar System? Observations: Orderly Motion - Conservation of angular momentum and energy lead to all particles orbiting into flat disk around host star - Anything that forms from disk maintains same angular momentum Explains 2 types of Planets - Ice beyond frost line contribute to larger planets that sweep more gas → Jovian - Dwarf planets, comets, asteroids are left over planetissimals that couldn’t form into planets - Asteroid belt: failed planet due to gravitational influence of Jupiter - Kuiper belt: lower density outer region of disk where things couldn't build up - Oort Cloud: comets are ejected outwards due to interactions w planets Exceptions: Moons Jovian Moons - Large # of leftover planetesimals beyond frost line - Since Jovians are massive, they accrete large planetesimals in random directions Terrestrial Moons - Small # of leftover planetesimals within frost line - Mars accrets small moons and Earth’s moon - Why is earth’s moon so big? Why is it bigger than the other terrestrial moons? How the Moon formed 3 competing Theories: 1. Formed along with Earth - 2 different collections of planetesimals came together around the same orbit 2. Formed separately then graviationally captured by Earth  3. After Earth formed and was in molten state, it spun so rapidly and split out the Moon Flaws in Models Joint Formation - gravitational interactions should've disrupted process, shouldn't have been possible for 2 objects of this mass to form along same orbit - Does Not explain why moon is less dense then Earth if from same material Capture - low probability of object the size of the moon pass by earth in right relative velocity to be captured - Capture requires loss of orbital energy, so harder to capture larger objects - Mars and the Jovian planets can capture small moons through friction force - gas in atmosphere heats up, taking energy from incoming moon - Earth’s atmosphere was never thick enough to capture the large moon Splitting - Earth was never spinning fast enough to break off into 2 pieces in fully molted state Apollo Missions - Earth rocks have different composition than Moon rocks → rules out joint formation - Moon must've formed somewhere else in solar system - Moon rocks contain no volatiles → easily vaporizable materials ex. Water, lead and gold at low temp - Should have volatiles if split from the earth New Model - Moon is less dense than the Earth - Comparable to earth’s mantle in density → no iron core or small - Composition of moon is similar to earth’s mantle Giant Impact Model - The moon is made out of material that accreted in earth's orbit after being blasted out of earths mantle - It being the same material of the mantle would explain the general resemblance - Violent blast would explain heat necessary for volatiels to escape - Early solar system was filled with planet sized bodies - some could've collided - Mars size planetesimals collided with new Earth and shattered both planetesimal and planet - then planet is completely molten, splashing debris into orbit  - Giant collisions explain case of Venus → rotating CCW then collision was strong enough to flip it upside down Implications for Life Beyond Earth - Other planetary systems should exist with significant diversity - range of types, orbits - Life friendly planetary systems are still numerous, even if rare bc. should be many palentary systems out there - Most of universe is older than sun (therefore older than earth) so lots of time to form other planets throughout our galaxy which suggests there are more advanced civilizations than ours if they had a few billion year head start Is the Universe Fine-Tuned for Life? Expansion of Universe - Too fast → galaxies won’t form - Too slow → universe would collapse in on itself - Expansion rate is just right for planets to form Ratio of Strengths of Different Forces - Force of gravity vs. electromagnetic force is balanced for organic molecules to form - Why? Isnt single universe but multiverse - conditions were not ideal, we just happen to be living in a universe that is - Something special about us - conclusion is risky bc. points to lacking necessary knowledge to interpret data - Higher beings responsible for fine tuning universe to get us to this point – 4D beings or tied to religion Week 5 Habitiability of Earth Part 1 Why is Earth so habitable? - Moderate temps - Abundance of water - Protective atmosphere - Stable environment Why are other terrestrial bodies not Habitable? - Venus is hot and high pressure - Mars has thin atmosphere and water is solid - Mercury and Moon are cratered, aireless, barren What makes Earth Special? Combination of: - Distance from the sun - Mass and size - These factors cannot be viewed individually → the moon is the same distance from the sun as the earth but has no life, venus is the same mass and size as thea earth - Determine a planet’s geology and atmosphere Geology’s Necessity for Existence - Study of any world with solid surface - Composition, geological processes on surface or within ex. Volcanoes - Important bc geology and life are intertwined → earth is habitable bc of its geology Volcanism - Volcanoes release gas trapped below surface after formation → leads to formation of atmosphere and oceans - Releases heat and create chemical environments that contribute to the origin of life - Only terrestrial planet that is volcanically active - Mars and venus were active in the past Plate Tectonics - Movement and recycling of rock - Responsible for moving the continents → mountains, canyons - Climate stability - Earth is the only planet with ongoing plate tectonics Magnetic Fields - Generated by charged particles in planets interior, creating a magnetic field - Acts as shield from solar wind from sun - Only terrestrial planet with significant magnetic field A Model for the History of Earth and Life Scientific Method Observations: - Cannot directly observe earth’s history - Methods for reconstructing earth's history from rocks and fossils: Geological Record - Solid objects preserve info from the time they became solid - Rocks → properties reflect its time of formation - Fossils → solid relics of organisms that lived and died a long time ago Rocks 1. Igneous - cooling and solidification of molten rock Aka. rock erupted from a volcano 2. Metamorphic - structurally or chemically transformed but NOT melted by high pressures/heat 3. Sedimentary - Gradual compression of sediments - Important bc most fossils are found in sedimentary rock → dies and is buried in sediments ex. Aquatic organisms buried on sea floor - Sediments produced by erosion on land: wind, water, ice break up rock - Small grains are carried by rivers and deposited to flood plains and pile up on sea floor, the sea compresses the rock - Record of time → sediments deposited at different times are going to look different due to changes in rate of sedimentation and type of organism - Strata (layers) → dinosaurs appear lower than primates - No single location contains the full geological record – can piece together Rock Cycle - Can evolve over time → tells us how its made - Does not tell us about its composition → must study its mineral content Minerals - Individual rocks contain a mixture individual crystals → each individual crystal is a mineral - 4300 different minerals discovered - Divided into Silicates (silicon and oxygen) and carbonates (carbon and oxygen based) Rock Analysis 1. Mineralogical analysis - What minerals are present - Tells us temp and pressure under which the rock was formed 2. Chemical analysis - Elemental or molecular composition of rock - Tells us what it is made of 3. Isotopic analysis - Ratio of isotopes - Tells us what processes might have acted on the rock - Different isotopes than nature, then something has acted on that rock Radioactive Isotopes - Has a nucleus that can undergo spontaneous decay - Decay happens at predictable rate → Allows us to find out how old a sample of rock is Alpha Decay - Nucleus emits helium nucleus Beta Decay - Spontaneous emission or absorption of electron - Conversion of proton to neutron or vise versa - When this happens, a different element is left behind Radiometric dating: ratio of certain radioactive isotopes and their products → serve as natural clocks - If you know the rate at which the element converts and you assume the start element, then you know the abundance ratio Isotope Half Life - time it takes for half the atoms in an isotope sample to decay radioactively - Important to study isotopes that have half-lives comparable to the age of the sample - Ex. if 20 days pass after you synthesize 1g of Ac 225 and you are left with 0.25g of Ac 225 and 0.75g of Fr 221, the half life of Ac 225 is 10 days Ex. Initially 100% K40 - 1 half life later it is 50% K40 and 50% Ar40 - 2 half lives later it is 25% K and 75% Ar - 3 half lives later it is 12.5% K and 87.5% Ar U-Pb Dating (Uranium & Lead) - Studying earths geological history - Uranium half life - 4.46 Billion years - Cross verification - calculate age of substance using 2 different elements → U238 and U235 - Verify they are the same are very close - certain how close estimate is - Reliable bc trial error, experience, cross verification as in other techniques Alt Methods - Tree rings - studying in trees - Labelled artifacts - Independent models - sun’s age of 4.5 Billion yrs and first planetissimals are comparable in age (radio dating in asteroids etc.) Reliability of Radioactive Dating Radioactive: is composed of matter with unstable nuclei - Measure unambious ages for igneous rocks with high accuracy → Uncertainty of 2% - Metamorphic rock is challenging - isotopic ratio are potentially altered over its history - Only put a lower limit on the age and talk about how its changed over time - Sedimentary rock - can try and dat individual grains and date igneous rocks above How we know whether or not life was present when a mineral was formed: Fossils - evidence of past life - Contains little to no actual organic material → minerals dissolved in ground water replaces organic matter - Only tiny fraction leaves behind fossil, most decay before it can occur  - Difficult to put together fossil record bc become rarer as we move into past - can be destroyed by volcanism, erosion etc. - 90% of Earth’s history lifeforms were microscopic - hard to find microscopic fossils - Estimates of when it began will be lower limits Age of the Earth - Oldest known earth rocks are 4 billion years old - any one older were melted or reshaped - Discovery of mineral grains of Zirconum Silicon embedded in sedimentary rock - solidified 4.4 billion years ago - Oxygen isotopes in grains suggest teh presence of water and formation of continents had already occurred - crust had already separated before 4.4 billion yrs ago (No longer hot molten planetesimal) - Earth formed quickly, then moon → 4.5 billion years ago Age of the Moon - Moon rocks → ideal for studying ages bc less affected by geological activities - 4.4 billion years old as well - Moon formed earlier 4.4 bil and earth is slightly older than moon (giant impact model) Meteorites: best evidence Young Meteorites - Fragments of asteroids that formed and later shattered via collisions Old Meteorites - Date solar system and earth - First pieces of solid materials to condense out of suns progenitor gas cloud - 4.5 billion years old - Earth and moon formed 50-70 mil years after oldest meteorites - relative age is easier than exact Inside the Earth when it First Formed Differentiation - Separation according to density - Before moon formed - Most lead sunk to core - first 30 mil years - Originally earth was completely molten, allowing separation by density Heating the Early Earth - Large worlds generate more heat bc more radioactive material in interior - Large Retain heat longer - longer to get from core to outer - Small cool quicker, geologically inactive much quicker Accretion - Acreeting meteors, asteroids etc, get gravitational energy converted into kinetic energy - Triggered melting of outer layers Differentiation - After accretion, ensured planet would completely melt and differentiate - Dense fall to interior, less dense floats - Creates thermal energy from gravitational energy - Caused all terrestrial planets to form cores and been cooling ever since Radioactive Decay - More radioactive materials decaying when arth was young, releasing heat - Present day dominant heat source Cooling Terrestrial Worlds *If a planet and its much smaller moon start off at the same temp, the moon will be cooler after 1 mil years bc it generates less internal heat 1. Convection: Carrying heat from mantle to lithosphere 2. Conduction - 2 objects touching, one is hotter and the other is cooler, heat will transfer - lithosphere to surface 3. Radiation: Energy is radiated off into space Relation to Our Solar System: Mercury & the Moon (smallest bodies) - Very highly cratered - no geological processes have smoothed them over during the heavy bombardment period - Little evidence of tectonic movement or volcanic activity - No atmospheres, so no wind effects or erosion Mars  - Believed to have been geologically active in the past → volcanoes on surface, evidence of atmosphere in past - Inactive today → interior cooled Venus - Same size as earth, expected to have similar geologcial activity as earth but inactive today - Very few craters, and very volcanically active in the past - Maybe tectonic plates What is earth like on the inside today? Evolutionary end-point to work back from: Density - calculation giving earth's mass and size - surface rocks are less dense than the average density and core is denser than earths average density Gravitational Field Map - Tells us how much mass is between the surface and centre Seismic Waves - Tells us about the structure of the earth's interior - Propagate through interior and anlong surface - Behavior depends on composition, density, pressure, temp, phase of the medium they are travelling through - Only earth and moon have had seismometers on them (map interior structure) - The rest → size of core is inferred by size and magnetism Vibrational waves - when wave is travelling through earth due to earthquake, where you detect P and S waves tells us what parts of earths interior is liquid bc bend the P and stop the S - Solid inner core, liquid mantle, solid crust P waves - vibration travels in same direction - Compression and stretching - Bend when passing through a liquid S waves  - perpendicular to direction travel - Side to side motion - Can’t pass through liquid Magnetic Field: Generated form planets interior, tell us what it's like on the inside Interior Structures: Core - Solid - high density material - Mostly metals with solid core and molten outer core Mantle - Rocky material with moderate density - Silicate minerals, surrounds core - Molten lava from volcanoes originates from mantle - Very hot to allow rock to deform and flow – allows or convection to get heat from core to surface Lithosphere - Low density rock - igneous: granite and basalt - Earth's outer skin Rock Strength - Depending on temperature and surrounding pressure, one sample can be much weaker than the other - Important when talking about mantle Week 6 Habitiability of Earth Part 2 RECAP: Why is Earth so habitable? - Moderate temp - Abundance of water - Protective atmosphere – shields us from solar winds - Stable environment, moderately constant Why are other terrestrial bodies not? - Mercury and Moon have no atmosphere, airless, barren, cratered - Venus is too hot, too pressured - Mars has a thin atmosphere, anything liquid will be in solid form What makes earth special? - Distance from sun - Mass and size - Volcanism, plate tectonics, and magnetic field are essential to earth's habitability - Earth geo records date back to 4.5 b - Earth was completely molten when it first formed – low density is near the surface and heavy near the core - Core mantle and crust emerged after the cooling — What happened once the Earth formed & Started to Cool? Model: The Geological Timescale Breaking up of earth’s history into distinct intervals of geological importance - Humans on earth less than 10 mil - Dinosaurs hundreds of millions of years - not right after earth was formed - Earth is 4.5 b years old 4 Eons: 1. Hadean: 4.5b 2. Archean: ancient life shows 3. Proterozoic: single-celled organisms  4. Phanerozoic: visible fossils - Eras (record is richer during recent times): Paleozoic, mesozoic, cenozoic eras - Humans represent 0.1% of earth's history and 0.3% of universe entirety Hadean - Early earth had No atmosphere or oceans, not large enough to accrete much gas - Living in this eon → lack of oxygen which is perfectly fine for many microbes - Impacts could have been sterilizing impacts - Underground life maybe survived but then extinct on short time scales, no fossils found but doesn't mean they didn't exist - Millions of years between impacts Heavy Bombardment from leftover planetesimals Period of intense meteorite and comet impacts on earth and other bodies in the early solar system - Planet formation did not use up every planetesimal - Some exist today as asteroid and comets - Most crashed into the sun or newly formed planets after formation - leave behind impact craters on solid surfaces - Earth experienced more impacts than moon due to stronger gravitational pull and a larger target - Most craters from heavy bombard on earth are erased by erosion, eruptions, tectonics - Use moon as guide post bc craters are preserved → lunar highlands are heavily cratered, 4 to 4.5 b yr rocks - Lunar maria (lava plains)→ crust is cracked and lava paves over surface, fills impact craters - 3.9 to 3 b years old - Debated Late heavy bombardment period, may have occurred 4.1 to 3.9 b years ago - Provides us with a means of dating - old were cratered bc subjected to heavy bombardment and smoother are younger due to geological activity Volcanoes - Earth's gas content came from planetissimals in outer region - flung inwards from collisions - Gas content trapped within earth when it first formed - Paved cratered surface, helped formed oceans Outgassing - 100m years after earth formed → 4.4b zirconium rocks suggest oceans presence on earth - Interior melting or formation of moon impacts outgassing - Molten rock erupts onto earth surface as lava - release of pressure expels trapped gasses - Via volcanoes or impacts  - Water vapour, co2, nitrogen, sulfur, hydrogen etc. and remaining gases formed atomospehre - Oceans and atmosphere formation → water vapor condense as rain to fill oceans - Early atmosphere: CO2 dominant, some nitrogen, no molecular oxygen - Now it is mostly 78% nitrogen, 20% oxygen, 0.1% CO2 Very little of the earthly atmosphere was nitrogen and oxygen, but now those 2 dominate Outgassing on Venus - Outgassing will have released the same contents as earth - Venus was closer to the sun which evaporated the water vapor, never had a chance to form oceans Plate Tectonics - Lithosphere was fractured into 12 places due to stress from mantle convection - Plates float over mantle - over, under, around eachother as convection moves interior rock, which is driven by heat released from interior - Movement - Few cm per year - Conveyer belt for lithosphere - Plays a role in regulating climate - Crashing of plates (psuhed each other up) creates mounting ranges - Plates pulling apart causing crust to thin - rift valley, new zone for seafloor spreading ex. Red sea - Slip sideways called fault - tension can create earthquakes - san andreas fault - pacific plate moving north interacts with north american plate moving south - Earth had a supercontinent 200m years ago - Over billions of years theyve been slammed together and pulled apart to form the different continents Earthquakes and Volcanoes - Don't always occur near plate boundaries – sometimes old or buried faults - Volcanoes occur when a plume of hot mantle material rises to make a hot spot - Hawaiian islands are a result of a hot spot on Pacific plate - most lava erupts on or around Big Island - 1 million yrs ago this Pacific plate lays closer to the south east Eruption - Descending seafloor crust heats up and melts as moving closer into mantle, may erupt upward if enough melting occurs - Explains high frequency of volcanoes near the edges of continents - seafloor curst is passing through continental crust into mantle Plate Tectonics throughout Solar System Moon, Mercury, Mars - Cooled fast and thickened up the lithosphere, no cracking - No convection bc of cooling, so no mechanism of cracking surface or moving plates Venus - Lack of plate tectonics, maybe high temps baked out water from crust and upper mantle, thickening lithosphere, preventing cracks - If hyp is correct, Trace cause of tectonics to 2 factors: - Heat driven mantle convection, lithosphere thats thin enough to be fractured by movement of underlying mantle Earth’s Magnetic Field - Movement of charged particles with molten metals in earths liquid core - Internal heat (necessary for magnetic field) causes liquid metals to rise and fall via convection - Earths rotation twists and distorts convection patterns of molten metals 3 Ingredients: - Conducting interior, convection, rotation = magnetic field - Earth is the only solar system that has all three - Venus has conducting interior and convection but very slow rotation rate - Mercury (iron core with weak magnetic field) and mars have rotation but no conducting interior and convection Importance of Magnetic Field - Atmospheric retention - prevents atmosphere from being stripped away by solar wind - Protection - solar wind contains harmful energetic particles Atomspheric Creation - Outgassing - Evaporation - Impacts & craters - vaporize solid mater into gas which populates the atmosphere Atmospheric Escape - Condensation into snow or frost (reversible) - Chemical reactions (reversible) - Atoms escaping into space (permanent)  - Stripping by solar wind (permanent) Gas Temp & Speed - Atoms can escape bc gas temp - Atoms move in random directions and speed depends on temp → hot moves fast - If they get too hot they can reach the escape speed → necessary speed to escape the massive objects gravitational pull - Earths escape speed is 11km/sec - Escape speed higher for more massive planets: square root of gravitational constant divided by radius Impacts - Impacts can be so energetic that they vaporize solid matter into gas - If planets escape speed is high (massive planet), gas can be retained - Of escape speed is low, gas escapes Thermal escape - At a given temp, lighter particles will move faster than heavier particles - Hot gas particles move at higher speeds that are more likely to reach escape sepeds - One way particles from atmospheres can be lost Solar wind stripping - Can strip a planet of its atmospehre over b of years - Earths magnetic fields acts like protective bubble against solar wind → defelcts most particles to the poles, creating the auroras Geology is Crucial to our Existence → earth’s climate Volcanism (atmosphere), magnetic field (atmosphere), plate tectonics - Earth climate has been stable for life to exist for 4 b years - Oceans remained partially liquid despite ice ages → important for life - Stability is surprising considering the sun is 30% brighter today → why haven't we over heated? - Earth’s Temp: Without atmosphere the average temp would be -16C → there would be ice everywhere - Current average is 15C with warmer periods in the past Greenhouse Effect - Visible light from sun provides energy → some absorbed ny surface and some reflected - Absorbed released via thermal emission (infrared light)  - Greenhouse gasses absorb and re emit infrared light, slowing its escape and warming the earth ex. Thick blanket lets less heat escape, not generates heat - Any element that absorbs infrared light - motions heat surrounding aire - In earth’s atomsphere: Water vapor, CO2, and methane - More greenhouse gasses make a planet hotter → 31C hotter today thanks to greenhouse g Global Warming - Human activity is adding more greenhouse gasses to atmosphere – strengthening greenhouse effect - Venus is ex. of runaway greenhouse effect → trapping all gasses and heating the planet - Carbonate rocks are the reason we dont have a runaway greenhuse effect on earth – rich in carbon and oxygen that are not found on Venus - Most of Earth’s CO2 is trapped in carbonate rock → the CO2 cycle CO2 Cycle Mechanism in which the CO2 is removed from earth’s atmosphere is stored in other places Important: over long periods of time, it acts as a thermostat to keep earth’s temp in a relatively narrow range 1. Atmospheric co2 dissolves in rain water - mildly acidic rain that brings co2 down to the surface 2. Erodes minerals that combine with carbon that get stored in the ocean floor 3. Minerals combine with carbon to make rocks in the ocean floor - Venus did not form oceans so had no way of trapping co2 in this manner 4. Continental drift carries rocks containing carbon down into earth's mantle - Plate tectonics and subduction (from ocean floor down into the mantle) - Venus doesn’t have tectonics 5. Rocks will melt in mantle and CO2 is outgassed back into atmosphere through volcanoes - Distribution of CO2 is not even throughout cycle and ratios can fluctuate - Most of early earth's co2 was dissolved in the oceans and converted into carbonate minerals - 60x as much co2 is dissolved compared to the atmosphere - 170 thousand times as much co2 is stored in rocks compared to atmosphere CO2 Cycle is a Thermostat  - Self-regulating feedback loop - temp returns to normal whenever it heats up or cools down - Temperature affects reaction rates of individual steps within cycle - Too warm → more percipitation and more co2 will be dissolved in rain, then co2 concentration will dissolve in atmosphere, which weakens greenhouse effect and it will cool earth - Too cold → less precipitation which will build co2 in atmosphere, which will strengthen greenhouse effect and warm the earth - Variations are possible bc the co2 cycle regulates on the 100 thousand year time scale - Climate change caused by humans cannot be corrected by the carbon cycle Ice Age - Several ice ages occurring in earth history – when global average temp drops by few degrees - Increased snowfall and continents freeze - Cause is unclear → could be suns gradual brightening, earths rotation axis which angles 23.5 degrees (responsible for seasons) and orbit - When axis is pointed towards the sun, northern hemi has longer days and is warmer and when hemi is pointed away from the sun, there are shorter days and colder - 24 hr dark days in winter in the north pole bc it is pointed away from the sun - If it were more inclined ex. 25 degrees, the summer would have longer days - Less inclined ex. 22 degrees, summer days are shorter and cooler, winters are colder and snow would build up year round - Removing ground water from the earth messes with spherical symmetry and fluctuates angle - Non-human caused fluctuations happen every 10 thousand years Snowball Earth (several long ice ages) - Global temp was -50C and oceans partially froze until 1km deep - Glaciers would freeze and travel all the way to the euaters - Cause is unknown, maybe once an ice age started, there is enough reflection of sun light allowing the planet to continually cool - End of snowball periods coincide with diversity of life in earth - owe our existence to the periods of intense winter - Carbon cycle to the rescue Week 7 The Nature of Life on Earth - Part 1 What is Life? (Astrobiology) - Earth is our only example of life in the universe - Life on earth is diverse → life beyond earth would be quite different - We would share some characteristics with life from other worlds - Defining life is difficult: wide range of sizes from microbes to animals - Range of environments so how do we come up with a definition that encompasses all life forms? - Need the right framework to define life - Life is something that can reproduce and evolve through natural selection What is water? Define by characteristics: - Wet, conforms to container, contains 2H and 1O, can be found in different states - BUT ethanol shares certain characteristics - Water can be easily defined in Particle Physics: H2O which is purely unique to water Shared Properties - Individual life forms share properties with things that are definitely not alive - Ex. cats and cars both requires energy, expel waste, can alter direction and move at varying speeds - Come up with list where “if it has x amount of properties it must be alive” 6 Necessary conditions but NOT sufficient on their own: Order - Material in living organisms always exhibit some type of order - Molecules arranegd in patters that make cell structures → structure allows for other properties of life - Though, other things have order like books, rock crystals, protein - Necessary condition for life (all life forms have it) Reproduction - Produce or are the product of reproduction - Some simple lifeforms can make an exact copy of itself like microbes - Complex have offspring that inherit genetic material  → Viruses - Smaller than bacteria, can’t reproduce on their own - Reproduce by infecting a living cell Growth & Development - patterns directed by hereditary traits passed to the organism from parents - Growth based on genetic instructions - All life passes on its heredity through DNA - Though, fire grows and develops Energy Utilization - Living organisms require energy to create and maintain patterns of order within cells, reproduce, grow and develop - Life without energy utilisation is not possible - Though, electrical appliances use energy Response to Environment - Interact with their surroundings and respond to environmental changes - Movement to more ideal temps for temp regulation - Thermostats respond to changes in environmental temp Evolutionary Adaptation - Evolution occurs as a result of interactions between organisms and their environment - Evolutionary adaptations make species better suited to their local environments - All living species are a result of evolutionary adaptation - Enough adaptation – a new species will emerge and others go extinct - Most fundamental → get the 5 from this - Only property that explains the great diversity on earth and understanding of it allows us to see how other properties came to be → Viruses - Evolove as product of errors during replication → mutation - Some mutations result in death or new virus Thermodynamics of Life - When left alone energy in any system undergoes conversion that lead to increasing disorder - Organism in closed system will use up all the energy - Get to place where no longer able to reproduce or fuel molecular processes, so they decay and die  - Living organisms require continous energy from environemnt → food, chemical or radiative reactions - Environment gains energy from internal (planet) or external sources (Star) - Life not possible on world without long-term energy source *Not a key property of life: ability to violate the second law of thermodynamics Role of Evolutionary Evolution in Defining Life Greeks - Suggested that life arose from water and evolved from simpler to more complex forms (Anaximander 610-547 BCE) - Creatures that poorly adapted to their environment died (Empedocles 492-432 BCE) Debate between Atomists and Aristotle - Atomists likely supported concept of evolutionary adaptation, though evidence is sparse - Aristotle claimed species are fixed, independent from eachother and do not evolve – adopted by christianity for 2000 yrs Theistic Evolution - Belief that biological evolution is a natural processes within the creation of the universe by God - 2 trains of thought → evolution occurs via natural process or it is guided - Whoever created the universe threw all the ingredients in knowing this is how its going to end up Rise of Evolution 18th Century - Gain traction - scientists began to suspect fossils represent extinct ancestors of living species - Bones are similar to species that occur on earth - maybe that’s what tehy looked liek in the past 19th Century - Jean Baptiste Lamarck suggested life-forms evolve by gradually adapting to perform successfully in their environments - Precursor to formal definition to evolution Observed Facts of Evolution - During lamarks time where he proposed his theory - Fossils fiffer in different layers of geological record → deeper is older  - Clear relationships between fossils and living - Theory of how evolution occurs remained elusive → lamarck suggested attributes gained during life could be genetically passed on to offspring Mechanisms of Evolution Charles Darwin - Origin of Species (1859) where he layed out a case for evolution in 2 ways: - Described observations of living organisms and demonstrated observations support that idea that evolutionary change does occur - Model of how evolution occurs, supported by evidence Theory of Evolution Fact 1: overproduction and competition for survival - Any pop has potential to produce more offspring than local environment can support, which leads to competition for resources Fact 2: individual variation - Individuals of pop vary in many inheritable traits, no 2 individuals are exactly the same and some possess traits equip others with better ways to compete for resources Leads to unequal reproductive success → Natural Selection - Natural selection is the mechanism by which advantageous genetic traits are preferentially passed on from parents to offspring - Heritable traits that increase survival will win out over less advantageous traits - Ex. finches of Galapagos Islands – each island has its own species of finch which can be explained by natural selection - Larger changes occur over longer periods of time - At the microbial level → allows for bacteria to become resistant to certain antibiotics and viruses evolve even faster where you can see it in days or months A Theory Emerges (from finches) - Extinct organisms are related to living organisms - Ex. fossils of giant armadillo are related to armadillos that exist today - Advantage to smaller armadillos surviving Artificial Selection - Evolution had long been on display in selective breeding of domesticated plants and animals - Dogs were bred from common ancestor with common traits  - If artificial selection causes profound changes over thousands of yrs, natural selection could do more over millions of years Molecular Basis of Evolution - Darwin didn't know how these traits were communicated across generations or why there were these variations among individuals, or how new traits appear – theory was observation based - Organisms are built from instructions cotnained in molecule called DNA (deoxyribonucleic acid) - Evolutionary adaptations related to changes in DNA over time - Theory of evolution has overwhelming observational evidence, understanding at molecular level, withstood tests, unifying theme of all modern biology - Can't be proven without a doubt, but no alternatives have been proposed Origin of Life - An ideal framework would encompass the origin of life - Molecular or chem evolution was underway until life arose from these organic molecules - Chemical evolution is comparable to natural selection → some energetic processes are favored over others under certain circumstances ex. Pressure - Would we recognize first life? In chem evolution, would we recognize that jump Searching for Life - Should be cautious when constraining our search for life elsewhere bc we have difficulty distinguishing the living and non living - No matter what definition we come up, it will be possible our definition will be incomplete, we someday encounter something that challenges the definition - Ability to reproduce and evolve through natural selection seems likely to be shared by most in the Universe Cells: Basic Units of Life - All living things are made of cells which are microscopic units that are separated from outside world by a barrier sometimes called a membrane - Basic structured of life, building block of life on earth - Living cells share many similarities → DNA passes hereditary info, they undergo similar chemical processes - Similarities are important for understanding the origin of life → maybe we all came from the same initial common ancestor when life began on earth - Every living organism on earth evolved over billions of yrs from the same origin of life Carbon-Based Life - All living organisms are nade of 20 different elements → mostly oxygen, carbon, hydrogen, and nitrogen - Oxygen found in water molecules - Molecules related to cell function structure and function contain carbon - Why Carbon? Bc if we look at universe as a whole in terms of element particles, it is mostly hydrogen (93%), some helium, and less oxygen - Those are gasses, so the stuff of the crust is mostly oxygen, silicon, etc. - Humans are made of more hydrogen and oxygen (water) than carbon, but the cells depend on the carbon for proteins - proteins that compose all known life are based on carbon Chemical Bonds - Sharing of electrons between atoms to form a molecule - Different element frim bonds in different ways → hydrogen only has 1 electron so only single bonds, not very versatile - Oxygen can only form up to 2 bonds, so not versatile either - Some bonds make both elements happier than other bonds, they want to be stable - Most stable when their valence electrons are full (outer orbital) - The higher the atomic number, the more it can form chemical bonds → it has more electrons to share ex. Silicon (14) will share more vs. Hydrogen (1) Carbon Bonds - Can bond with itself - up to 4 bonds, form double bonds, which are very strong - Ideal for serving as the basis for life bc it can form strong bonds with itself - Allows carbon atoms to link together and from skeletons that vary in size and branching pattern - Carbon molecules associated with life bc of their strength, versatility to bond with itself - Hydrocarbons → carbon bonded with hydrogen What About Alien Life? - Since chemistry, biology, physics appear the same throughout the universe, why wouldn't it be different → We are dealing with the unknown - Any element that has 4 valence electrons that want to bring in 4 more, could theoretically do what carbon does, so why couldn't life be Silicon or lead based? - Though it is abundant on earth (more than Carbon) and can form 4 bonds, the bonds would be weaker, and it rarely forms double bonds, silicone dioxide in earth-like environment is a solid, no dissolve - Maybe silicon life based in the earth's past but carbon based life won out on selection, so it is not ruled out bc we want to recognize alien life if we detect it Week 8 Nature of Life Beyond Earth - Part 2 Molecular Components of Cells Components made from complex organic molecules: 1. Carbohydrates - Energy storage and structure - Any kind of life form needs energy and some sort of structure to keep it separated from the outside world 2. Lipids - Used for energy storage → fats - Key ingredient in membrane - Spontaneously form membranes in water, trapping organic molecules - Important for origin of life 3. Proteins - Functionality → workhorse of the cell - Structural elements and biochemical reactions → enzyme ex. catalyst (substance that facilitates or accelerate a specific chemical reaction) that doesn't get changed our used up in the process → Amino Acids - Small molecules that when chained together build proteins - 70 known types of aminos → life builds from 20 of them - Same versions of the same aminos seen in living cells, points towards common ancestor 4. Nucleic Acids DNA: basic hereditary material of life on earth, evolution is the result of DNA RNA: Ribonucleic acid that carries out the instructions imbedded in DNA Framework for Classifying Life Microscopic Life - Bringing together these materials allows us to subclassify life  - Dominant life form on earth in terms of mass and volume → microscopic mass is more than non microscopic so uses up the most space - More likely to find microbial life beyond earth than nonmicrobial - Diverse in size, structure, biochem, and genetics - Most harmless to humans, many crucial to our survival (internal and external) - Plant and animals life would not exist without microscopic life Complex Life Large multicellular organisms - Plants, animals fungi etc. 3 Domains of Life - Comparison of DNA, greater similarity the closer they are related - Bacteria (microbes), Archaea (microbes), Eucharya (micorbes also complex life) - Astrobiology → large multicelluar represent 3 branches of Eukarya (animals, plants, fungi) - Branches represent amount of difference between species, root represents common ancestor - Diversity of life on earth is found in the microscopic realm – We’re closer to fungi than two bacteria are to each other What Do Cells Do? Metabolism - Chemical reactions that occur in living cells to provide energy and nutrients - Process that takes place within a cell - Reactions are aided by cell itself, which effectively acts as a chemical factory → too slowly in nature without a cell - Makes things happen at the appropriate rates to stay alive - Turns simple molecules into complex molecules → can break down or build up - Fast or slow metabolism for human bodies are the ability of enzymes Water - All living cells depend on water for metabolism → metabilism requires organic molecules to be readily available for reactions, water makes this possible bc molecules float in the cell - no organism can survive without water, some liquid is necessary for life - Why water? Medium of transport, allows organic molecules to interact - Oxygen in water is electronegative, strongly pulls electrons shared with hydrogen towards nucleus (H2O)  - Strong bonds make it very stable - Charge distribution is uneven or polar → Good at breaking apart other bonds resulting in dissolution - Liquid range is 0-100 degrees What about other molecules? Methane - Abundant solvent in solar system (liquid form) - Saturn’s moon Titan has methane filled lakes - If methane can serve the same role that water does on earth, maybe theres a way for life beyond earth - Not polar/electromagnetivity, narrow temp range where it is liquid, weaker H bonds than water so not as strong or stable Biochemical Manufacturing – 2 requirements: 1. A source of raw materials 2. Source of energy - Cells able to build a variety of products with limited materials ex. Diversity of enzymes are made of same molecules but arranged in different patterns to serve a different function Carbon Sources & Energy Sources - In animals, cells make use of molecules from food sources - Other life forms use sunlight or chemical reactions for energy - Variety of carbon and energy sources is encouraging for existence of life beyond earth ex. Mars – but missing if these individual cells can come together and have metabolic processes Summary - Complex metabolism requires structures that allows carbon and energy to come together - Manufacturing of molecules needed for life - All living organisms must have a fundamental structure that functions like earth-cells - We can search for life in the universe by searching for cells instead of wide range of possible structures DNA & Heredity DNA Double helix backbone linked with bases 4 bases: - Adendine, cytosine, guanine, thymine - Only 2 bases can pair at any time → (A + T) and (C + G) - An organisms heredity is encoded in DNA - Artificial engineering of 4 other bases, so possible in life beyond earth Heredity - Operating instructions are contained in the precise arrangement of chemical bases - The order of the pairs contains the instructions - Building proteins, carrying out or regulating building processes - Instructions representing individual function make up a gene (set of base pairs) - 95% of DNA is useless, noncoding – not used in passing of generations - Maybe there is something in this junk, evolutionary artifact maybe something a long time ago used all of the genetic material - Maybe we lack the knowledge to interpret the junk, maybe there is more to learn RNA + Roles - RNA is similar to a single strand of DNA - Different backbone and one different base (uracil instead of thymine) - Carries out genetic instructions in the cells → different types of RNA allow for transcribing DNA, collecting and assembling molecules - Important role in the creation of the first life form How does Life Evolve? Mutations - Genomes can be replicated quickly with errors occurring in >1bil bases copied - Complex organism errors occur more often: - Wrong base may het attacked to base pair - Extra base may be inserted into gene, base may be deleted - Entire sequence of bases duplicated or eliminated - Radiation, UV light, chemicals can cause error - May have no affect at all → ex. ACC gets turned into ACA results in same amino acid - May change single amino acid in protein, anf can have minimal functionality effects - Can be traumatic, and if it survives, mutation will be copied every time DNA is replicated and can permanently change heredity Basis for Evolution - Mutated cells that are passed on to offspring result in genes that differ from parents - Mutation can occur in egg or sperm cell and be passed but not a mutation from liver cells - Leads to variation among individual species - Some genes will provide advantageous adaptations to the environment - Individual variation among species + population pressure = natural selection DNA & Life on other Worlds - Heredity is crucial for any life form to store operating instructions and pass them to offspring - DNA is the carrier of heredity → maybe first life forms had RNA in the past and surprising if the very frist life forms used complex DNA to reproduce - Other molecules may be able to carry heredity that functions like DNA to form life, possible to have DNA like double helix but with different base pairs Life at the Extreme - Understanding how life can exist in extreme environments tells us alot about how life can exist on other worlds - Organisms that have evolved to thrive in environments that are lethal to humans are called extremophiles - Most are bacteria or archea - Some an live in normal enviroenmnts too, some can only live in extreme conditions - HydroThermopiles with enzymes that only function at high temps - Microbe and fungi living in driest places on earth ex. Slopes of volcanoes in Atacama desert comparable to Mars (huge temp jumps, high UV radiation, less than 5mm of rain per yr) - Dry valleys of Antartica is also Mars like – always below freezing, no rain or snow but life survives inside rocks like endoliths in water pores - Surface lifeforms are not the dominant species of earth in terms of total mass or volume Diversity of Life - Humans are not the dominant form of life on earth, neither are plants and animals - Microbes and extremophiles make up most of earths life by mass and number Conditions for Life Chemical basis of life on Earth imposes limits on the conditions for life: - Too cold → organisms freeze, proteins are immobalized, structures rupture  - Too hot → breaks bonds with proteins, protein denatures (change in shape and functionality) - Originally thought limits were between 0C and 100C (boiling and freezing points) Volcanic Vents - Hot water and rock released near ocean floor - Connection between mantle and crust - Temp of 350C but water stays in liquid form due to pressure - Most organisms would not survive near these vents - Microbes discovered living and thriving in these regions Thermophiles & Hyperthermophiles - Many organisms prefer temps above 100C - Adapted to use stronger bonds to preserve proteins at high temps or re-fold dentatured proteins - Many hyperthermophiles are archaea (single-celled) → earliest forms of life on earth - Maybe life began in hot thermal vents? Evolution as a Science Is Evolution a Fact or theory? Evolution is a Fact - Geological record and observations of modern species show that living organisms cna change over time – see fossils that are closely related but not the exact same as species today - Theory of evolution explaisn how and why these changes occur - details like rate of change still debated and relationship between some species are still debated - Situation is analogous to gravity being a fact – things fall when we drop them but whether it is newtons law of gravity or einsteins law of relativity Evolution & the Hallmarks of Science 1. Explains observed phenomena that rely solely on natural causes – natural selection 2. Science progresses through the createion and testing of models – ideas of evolution won over aristotle, darwin's model replaced lamarcks model with better observations, molecular model of evolution is a refinement of darwin's model 3. Scientific model must make testable predictions that would lead to revising or abandoning the model if predictions do not agree with observations – molecular model of evolution predicts diseases can evolve in response to medication designed to fight them,  genetically similar species should respond to medication in the same way → provides a road map for modifying organisms through genetic engineering - No scientific alternatives to evolution exist that also follow the Hallmarks of Science and “Western” science Understanding vs. Belief - Alt can befound in other cultures and religions that don't follow hallmarks - Some oppose theory of evolution due to beliefs - No theory can be proven without a doubt – new observations are inevitable Comapartive Evolution - Discovering life beyond earth would open up a new field of study - Open up idea of comparative evolution – exploring the similarities and differences among living organisms on multiple worlds - Different origins? Histories? Revision or replacement of Theory of Evolution? Week 9 Origin & Evolution of Life on Earth - Part 1 Pre-class video Alternative theory: Life Migrated to Earth Panspermia - Building blocks for life can form and remain stable in the space environment → gas clouds, asteroids, comets - Some exremophiles can survive moderate periods of time in space - Can life migrate from planet to planet? Meteorites - Capable of travelling from one world to another - 100 meteorites found here on earth originated from Mars and more came from the Moon → possible bc meteorite blasted away from home world by impact and made its way to earth - Earth, venus, and mars have exchanged kg’s of rock since they were formed Survival For a microwave to arrive intact on Earth it must survive: 1. The impact that blasts it off the surface of its home world 2. The time spent in space *most difficult or prime issue 3. Fiery plunge through earth's atmosphere → high velocity and friction due to air resistance - Probability of microbe surviving the trip between planets depends on duration of journey - Most meteriotes from Mars took mil of years to reach Earth - 1 in 10 thousand took less than a decade – ISS experiments suggest microbes can survive 10 yrs in space or longer in rocks Starseed - Migration between star systems unlikely bc trip is mil to bil years in space - Along the way, asteroid is exposed to cosmic rays – high energy radiation, protons that travel trhiygh space near the speed of light caused by stars - Risk drying up of any water and probability of striking another planet is very low - Ex. Omuamua came from another star system, moving too fast to have originated from our solar system, suggested that it is an alien artifact - Left its parent system 4.5 bil yrs ago, altered by cosmic rays along the way and entered the solar system in the 90s  - Controversy to if its real: Experienced a non-gravitational acceleration while passing the Sun, predicted what teh orbit should be and it deviates from path, nothing to do with gravitational interaction with sun - Some source acted on the Omuamua and changed its course, could be outgassing but did witness any, or knocked off by solar wind, or artificial thrusters that changed direction IM1 (interstellar meteor 1) - Observed by US defence as it entered the atmosphere - Attempts to reverse its orbit suggests that the interstellar origin is possible, though with large degree of uncertainty - Controversial claim that iron fragments have been recovered from bottom of Pacific that are from IM1 Reasons to consider Migration - Maybe life does not form as easily as we think - Only 1 or few worlds have the right conditions for creating life - Just moves problem of creation to another location - how did life originate on earth to elsewhere - Goes against signs pointing to early earth having the right conditions fro life Flip side - Live arises very easily - Should expect life to originate on any planet with suitable conditions - Origin of life occurs on planet in solar system that had the right conifiotns first - Whichever one formed life first formed the seed - maub weary Venus or Mars was the better suitor for life before earth - They migrated from Venus or mars - maybe earth never had a chance to from indigenous life - Earth has life for whatever reasons - can earth based microbes hitched a ride to Mars or other bodies - If we discover life elsewhere or evidence of past life, could we be confident that it did not originate from earth, would we be able to tell indigenous origin on earth or migration? - It is possible life m