Unit 7 Topic 3.1 Early Origins PDF

12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System Unit 7 Topic 3.1 Early Origins TOPIC 3.1: Early Origin of the Earth Systems...

12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System Unit 7 Topic 3.1 Early Origins TOPIC 3.1: Early Origin of the Earth Systems Module 1 Intro (https://canvas.ubc.ca/courses/148569/pages/m (https://canvas.ubc.ca/courses/148569/pages/introduction) 1-building-the-solid-earth-2) Topic 3.1 Lecture Video Recording: HERE (https://canvas.ubc.ca/courses/148569/pages/video-topic-3-dot-1) Note: Although lecture recordings cover the same material as the notes below, you should use the notes as your primary source for this topic concerning exams and tests. Topic 3.1 Rationale / Sample Questions / Final Exam Focus Areas Rationale: To Examine the origins and early history of the Geosphere, Atmosphere, Hydrosphere and Biosphere. Sample quiz questions: HERE (https://canvas.ubc.ca/courses/148569/quizzes/764687) (Note: this quiz does not count towards any course points; you can take it as many times as you like). 2024 Fall Final Exam Focus: HERE (https://canvas.ubc.ca/courses/148569/pages/final-exam- focus-questions) Topic 3.1 Learning Goals. By the end of this topic, you should be able to: Account for the origins of the non-living biosphere Define life and its common features. List the possible scenarios for the development of organic molecules. Describe the formation of cell components. Describe possible Earth-based locations, mechanisms of life's origins Note: Learning Goals are intended to help you understand the main themes of the topic. They are not designed as a guide to the exact content that will appear in exams. https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 1/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System Topic 3.1 Outline 3.1.1 Origin of the Non-Living Earth Systems 3.1.2: The Biosphere 3.1.1.1: The Geosphere 3.1.2.1: The Common Features of Life 3.1.1.2: The Atmosphere 3.1.2.2: Origin of Life's Building Blocks 3.1.1.3: The Hydrosphere 3.1.2.3: From Building Blocks to Cells 3.1.2.4: Where Did Life Emerge? 3.1.3 Summary Topic 3.1 Required Additional Materials Please review the following article: HERE (https://www.sciencedaily.com/releases/2011/03/110321161904.htm#). This forms part of the material required for the unit 7 additional materials quiz: HERE (https://canvas.ubc.ca/courses/148569/quizzes/764642). Topic 3.1 NOTES IF YOU WANT TO MAKE A COPY OF THESE NOTES: Save as a PDF, BUT DO NOT SHARE IN ANY FORMAT! It must be for your personal use ONLY! You can Print or make a copy using the "Print" option in your browser (usually found under the "File" option) and then "save as a PDF"). If you have difficulties with this, please contact the course instructor. In section 1.1.2.1, we considered how Earth can be viewed as four major interacting systems: the Geosphere (all materials from soils at the surface to the center of the planet), the Hydrosphere (all water on the planet, including the oceans), the Atmosphere, and the Biosphere (all living or once- living materials). In this topic, we will consider how these systems emerged, particularly emphasizing the biosphere. NOTE: this topic includes an additional required video, RNA WORLD (https://www.youtube.com/watch?v=K1xnYFCZ9Yg) , in section 3.1.2.3a. 3.1.1 Origin of The Non-Living Earth Systems 3.1.1.1 The Geosphere The origin and current structure of the Earth were explored in Topic 1.3, but when and what was the first solid surface to form on Earth, and when did plate tectonics initiate? 3.1.1.1.a) The oldest crust. The oldest crustal fragment on Earth is the Acasta Gneiss (350km north of Yellowknife, NWT, Canada) at 4.04GA. Gneiss is a metamorphic rock deformed by high pressure https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 2/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System and temperature. Before metamorphism, the Acasta Gneiss was a "granite-like" rock in an ancient continent. You can see a sample of the Acasta Gneisses in the Pacific Museum of the Earth at UBC (Figure 1 left). We have even older evidence of a solid surface from zircon crystals, some of which have been dated to 4.4GA! This is older than the Acasta Gneiss, but these crystals were eroded from an even older rock (probably a granite) and included in a younger sedimentary rock called the Jack Hills Conglomerate (Figure 1-right). Figure 1: The Acasta Gneiss in the Pacific Museum of Earth, UBC (Left), The Jack Hill's Conglomerate Zircons (right) 3.1.1.1b) Initiation of Plate Tectonics. Estimates regarding the onset of plate tectonics range widely, from approximately 4 billion years ago to as recent as 800 million years ago. Interesting evidence about the onset of plate tectonics has been obtained from diamonds. Diamonds within Earth's mantle are brought to the surface of the Earth via volcanic activity. During the diamond formation, certain materials become incorporated into their structure (Figure 2). These "inclusions" have been examined by Dr. Steven Shirey at the Carnegie Institution, revealing a significant shift in the chemical composition of diamond inclusions approximately 3 billion years ago. Figure 2: A Dimond with Inclusions In the earlier inclusions, peridotite - the rock constituting most of the Earth's mantle - was the https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 3/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System predominant material. Conversely, inclusions in more recent diamonds contain eclogite, which forms when oceanic crust is subducted into the mantle (see Topic 2.5). Remarkably, no inclusions composed of eclogite have been discovered with an age exceeding roughly 3.2Ga. This evidence strongly suggests that the initiation of plate tectonics likely commenced at that time. Before 3.2Ga, Earth’s mantle may have been too hot (and therefore too buoyant) to allow the lithosphere to subduct. Like much of Earth's early history, this is still a great area of scientific debate. A video describing the research of Dr. Shirey can be viewed HERE (https://www.pbslearningmedia.org/resource/buac16- 612-sci-ess-nvtectonicsbegin/when-did-plate- tectonics-begin-treasures-of-the-earth/) Note: Any information in the video beyond that provided in 3.1.1.1b) is not examinable. 3.1.1.2 The Atmosphere The atmosphere, or "air" of the Earth today, is retained by Earth's gravity and protected from the effects of solar radiation (that would strip away the atmosphere over time) by Earth's magnetosphere (see unit 4). Dry air contains the following gasses: 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide and small amounts of other gases. Air also contains a variable amount of water vapour. The Atmosphere has evolved over time. Initially, the Earth would have an atmosphere similar to the gases in the solar nebula: mostly hydrogen and helium. However, solar winds would have stripped these gases away from the Earth when the sun initiated nuclear fusion. The next atmosphere developed volcanically as the hot interior "outgassed," a process still occurring today. The composition would be similar to current volcanic gas emissions: carbon dioxide, hydrogen, nitrogen, chlorine, sulphur-based gases, and water. Unlike Earth's initial atmosphere, the formation of Earth's core and the magnetosphere (Unit 4) would allow this atmosphere to be retained. It is estimated that water would have made up around 60% of this atmospheric phase, with carbon dioxide varying between 10 and 40%. Compare that to today, where nitrogen comprises approximately 78%, oxygen 21%, 1% Argon and trace amounts of carbon dioxide and other gasses. Our atmosphere has undergone considerable change! Volcanoes likely supplied nitrogen as the planet degassed. Nitrogen is relatively inert and is not used to form solid Earth materials or involved in many chemical reactions in the atmosphere. Unlike https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 4/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System gasses such as carbon dioxide, very few "nitrogen sinks" can take the gas out of the atmosphere and store it elsewhere. As such, nitrogen has gradually built up to its current 78% level over time. The evidence of oxidized (Ferric-Fe3+) minerals like Hematite (Fe2O3) in rocks suggests that Oxygen entered the atmosphere around 2.3 billion years ago. The Oxygen probably came from photosynthesizing cyanobacteria that released oxygen as a waste product. Iron in its Ferrous soluble state (Fe2+) was initially present in high concentrations dissolved in the Earth's oceans, added through hydrothermal vent systems on the ocean floor. The oxygen produced by the cyanobacteria would rapidly oxidize the dissolved Ferrous to Ferric (Fe3+) minerals in the oceans. Ferric iron is insoluble, and this process probably accounts for the deposits of iron-rich rocks called Banded Iron Formations. Eventually, though, the amount of oxygen produced by cyanobacteria not only oxidized all the Ferrous iron in the oceans, but the excess could bubble out of the oceans and start accumulating in the atmosphere, oxidizing any iron minerals on land (Figure 3). Figure 3. Red desert sandstones, Devon, England. Hematite, an iron oxide (Ferric Fe3+), causes the red colour. Before oxygen entered the atmosphere at around 2.3 GA, continental sedimentary rocks like these are green, the colour of iron minerals in a Ferrous (Fe2+) state. (Image: Sutherland) 3.1.1.3 The Hydrosphere Oceans form the major component of the Hydrosphere, but where does all that water come from? While comets were once considered a prime source, their isotopic composition doesn't align with that of Earth's oceans. Instead, asteroids, particularly carbonaceous chondrites, offer a more compelling explanation. These asteroids, rich in water-bearing minerals, likely delivered significant amounts of water to our planet during its early history. As these asteroids collided with Earth, the impact would have released the bound water, contributing to the formation of our oceans. The greatest source of water, though, is probably volcanic. During the planet's formation, water-rich materials were incorporated into its interior. Over time, this water has been gradually released from Earth's mantle via volcanic activity. This process, known as outgassing, has replenished the oceans and atmosphere. It also accounts for why Earth's mantle today is relatively "dry." https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 5/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System 3.1.2 The Biosphere 3.1.2.1 The Common Features of Life The biosphere encompasses all living organisms on Earth (Figure 6). But what exactly is life? Defining it beyond the simple phrase "something living" is surprisingly complex. This definition may come close: The condition that distinguishes animals, plants, bacteria, and archaea (a type of microorganism) from inorganic matter. Characteristics of life include being separated from the external environment by a barrier and possessing the capacity for growth, reproduction, functional activity, and evolution. Even with these criteria, a comprehensive and universally accepted definition of life remains elusive. Figure 6: "Life!" A condition that includes the smallest bacteria, orangutans, fish, and so much more... Life is an intriguing phenomenon composed of non-living elements that exhibit unique properties when organized within a cell or organism. For instance, a cell consists of various substances abundantly found in the non-living universe. However, these components manifest life properties only when combined and enclosed within a cell membrane. This suggests that life can be understood as an emergent property, wherein living cells represent something greater than the sum of their individual parts. The concept of emergence is widespread in biological systems. Consider an ant colony: while an individual ant may have limited capabilities, collectively, they can achieve remarkable feats. Ant colonies can construct complex structures, engage in agriculture by farming fungi or aphids, defend their territory, or launch attacks on neighbouring colonies. This illustrates how emergence operates, where the combination of simple components results in the emergence of complex behaviours and structures that are not present in the individual components alone. Another property of life is that it works against entropy. Entropy is the name given to how the universe, over time, becomes increasingly disordered and energy becomes spread out. According to some physicists, the universe's ultimate fate is to become very cold and disorganized with no structures like stars or galaxies, the so-called heat death of the universe. Don't worry about this too much, though, as (if it occurs) it is still 1.7x10106 years away. Life, however, works in the opposite https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 6/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System direction to entropy; it locally creates order and concentrates rather than spreads energy out. Of course, entropy eventually wins out when organisms die. Cellular life can be divided into three major domains: bacteria, Archaea, and Eukarya. Bacteria and Archaea are classified as prokaryotes, single-celled organisms that do not have a nucleus enclosed by a membrane. Instead, their genetic material is freely floating in the cytoplasm. Unlike eukaryotic cells, prokaryotes also lack complex organelles; specialized cellular structures that perform specific functions. Eukaryotes (Figure 7-bottom) are organisms whose cells have a membrane-bound nucleus containing their genetic material. They also possess complex organelles, specialized cellular structures that perform specific cellular functions. Eukaryotes include protists, plants, fungi, and animals. In general, eukaryotic cells are significantly larger than Figure 7: Prokaryote (top), Eukaryote (Bottom) prokaryotic cells. For more information on this Note: you are not required to know the details of this figure beyond that topic, see his video: Domains and mentioned in the text of this Topic LadyofHats, Public domain, via Wikimedia Kingdoms of Life Commons / Mediran, CC BY-SA 3.0, via Wikimedia Commons (https://www.youtube.com/watch?v=BnDRJAt- 4aM). Note: Any information in the video beyond that provided in the paragraph above is not examinable. All cellular life-forms exhibit the following features: 1. They work to maintain homeostasis (a stable internal environment) within the cells. 2. They generate energy to power cellular processes. 3. They possess a membrane that separates them from the external environment, creating a closed system. 4. They have molecules (DNA and RNA) containing information for building structures https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 7/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System within the cell. 5. The information molecules must have the capacity to evolve via natural selection as reproduction passes copies into the future. Viruses are simpler than cells and have sparked debate among scientists about whether they should be considered living organisms. While viruses can reproduce, they can only do so by hijacking the machinery of a host cell. Unlike cells, they cannot produce their own energy or maintain a stable internal environment (homeostasis). One interesting question is whether viruses or cells evolved first. This topic is complex and ongoing, but we won't delve into it in this course. If you're interested in learning more, you can find additional here: Are Viruses Alive Video (https://www.youtube.com/watch?v=X31g5TB-MRo) : Note: Any information in the video beyond that provided in the paragraph above is not examinable. 3.1.2.2 Origin of Life's Building Blocks To understand the origin of life, we must first consider the fundamental building blocks that makeup living organisms. On Earth, carbon is the preferred element for life. While it's less abundant on our planet than silicon, carbon can form strong bonds with itself and other elements, creating a wide variety of molecules with diverse properties. Although silicon is more abundant in Earth's crust and can also form complex molecules, life is probably carbon-based because carbon bonds are generally stronger and more stable in water than silicon bonds. For a more detailed exploration of why carbon is the preferred life element, see HERE (https://www.youtube.com/watch?v=kAFC4RY1cKQ). Note: Any information in the video beyond that provided in the paragraph above is not examinable. All living organisms, except for viruses, are made up of cells composed of various organic molecules. These molecules include carbohydrates, lipids (fats), amino acids (the building blocks of proteins), and nucleobases (the "letters" of the genetic code in DNA and RNA). Organic molecules are compounds containing carbon and hydrogen atoms. Organic molecules were initially called "organic" because it was once believed that only living organisms could create them. However, we now know that organic molecules can also be formed naturally in the non-living universe without the involvement of life. Let's explore some of the possible sources of these fundamental building blocks... 3.1.2.2a) Extraterrestrial Sources Our planet likely received some of its organic building blocks from space. Scientists have detected organic molecules called polycyclic aromatic hydrocarbons (PAHs) in nebulae within our galaxy. These PAHs are ring-like structures that sometimes form spheres called "buckyballs" (Figure 8-right). It's estimated that around 20% of all the carbon in the universe might be PAHs. Within our solar system, carbonaceous chondrite meteorites, like the Murchison meteorite (Figure 8- left) that fell in Australia in 1969, have been found to contain a variety of organic molecules, including over 15 different amino acids, the building blocks of proteins! Similarly, analysis of material collected https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 8/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System from comet Wild 2 by NASA's Stardust mission in 2009 revealed the presence of the amino acid glycine and other organic compounds. These discoveries strongly suggest that some organic molecules essential for life on Earth may have originated in space and arrived here through meteorites and comets. To discover how we sampled a comet Wild 2, see the following NASA video HERE (https://canvas.ubc.ca/courses/148569/pages/2024-25-nasa-stardust) (not examinable material). Figure 8: The Murchison Meteorite (left); Polycyclic Aromatic Hydrocarbons - PAH - buckyball (right) 3.1.2.2b) Atmospheric Sources Urey and Miller at the University of Chicago designed an apparatus to recreate the conditions of early Earth using water, ammonia, methane, and hydrogen to approximate the planet's primitive atmosphere (Figure 9). The chemicals were placed in a closed glass tube system, with one vessel containing liquid water representing the ocean. The water was heated to create water vapour, and electrical sparks simulated lightning. The energy from the sparks helped break down some of the gas molecules, allowing them to recombine in different ways in the way that they would have done billions of years ago in Earth's atmosphere. Figure 9: The Urey-Miller Experiment The resulting materials were then cooled and Adjusted from Levin - The Earth Through Time, Figure 8-37 condensed, collecting in a trap. https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 9/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System After just one day, the solution in the trap turned pink and, after a week, a deep red colour. Analysis of this liquid detected a variety of amino acids. Ideas regarding the composition of Earth's early atmosphere have changed since the original experiment; even so, the experiment still readily synthesizes many of life's building blocks with different atmospheric starting materials. It is possible that organic molecules were literally "raining" from the skies of the Early Earth. 3.1.2.2c) Oceanic Hydrothermal Vents For a more geological origin of organic molecules, we need to consider hydrothermal vents; hydrothermal vents occur in two locations on the ocean floor, both characterized by plumes of hot water escaping from the Earth's crust. 1) On-Axis "Mid Ocean" Ridge Vent Systems Rather than "mid-ocean" we should probably refer to these as "on-axis" meaning the active ridge axis of a divergent boundary; spreading ridges do not always occur "in the middle" of an ocean. As discussed in Topic 2.4, these divergent ridge systems represent areas where the oceanic lithosphere is being constructed. Water seeps down through fractures and faults in the crust and is superheated by the hot rocks and magma at depth. The fluids released at hydrothermal vents at midocean ridges are black, very hot (250 - 400°C) and acidic (Figure 10). The black colour is caused by iron sulphide stripped from rocks as the hot water travels through the crust. Check out THIS (https://en.wikipedia.org/wiki/Hydrothermal_vent) video from NOAA of a black smoker vent system. In addition to iron sulphides, minerals such as copper, zinc, and other metals are present. Initially, it was thought the minerals in these systems could have acted as catalysts, helping to form organic molecules from CO2 dissolved in seawater. Unfortunately, any organics that may form in this environment would remain stuck to the catalysts, making them unusable. In addition, although these vent systems support a diverse ecosystem today, it is unlikely that such hot and acidic waters would have been favourable for forming relatively delicate organic molecules needed for life. Another problem lies in the activity in these systems; activity on a ridge can be sporadic and remain inactive for long periods. We need to look at a different type of vent system as a possible source... https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 10/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System Figure 10: Hydrothermal Vents at a Mid-Ocean Ridge System. Left: A Black Smoker.Right: A schematic cross-section through a Mid-Ocean Ridge system highlighting the system's chemistry (you do not need to know the details of this figure). 2) Off-Axis Vent Systems By "off-axis," we mean that these vents are not located on the active axis of the spreading ridge but quite a distance away from the volcanically active ridge systems. Rather than "black smokers," these off-axis systems are characterized by "white smokers" Figure 11-left. Barium, calcium, and silicon minerals produce the lighter colour in these systems. Although still very warm compared to the surrounding ocean water, white smoker vents are cooler (around 60-90°C) and are alkaline with a pH of around 9, similar to baking soda. Since these regions are no longer volcanically active, what fuels the activity at these hydrothermal vent systems? The process of serpentinization plays a key role. Areas with white smokers are often located near faults that have brought deep oceanic lithosphere material - peridotite - closer to the surface, allowing seawater to interact with these rocks. When seawater encounters the mineral olivine in peridotite, an exothermic (heat-generating) chemical reaction occurs. Oxygen from the seawater combines with iron in the olivine, creating magnetite and releasing hydrogen gas. The hydrogen produced can react with dissolved carbon dioxide in the seawater to form organic molecules. Unlike vent systems at mid-ocean ridges, off-axis vent systems are not dependent on volcanic activity and, therefore, have a much longer lifespan and the possibility of producing more complex organics over a longer periods of time. https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 11/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System Figure 11: A White Smoker Vent (left), Peridotite - most of the green colour is the mineral olivine (middle), Schematic cross-section through the oceanic crust (right), 3.1.2.3 From Building Blocks to Cells How do you go from a soup of organic molecules to the first living cells? As noted above, to form a cell, you need molecules that can store information that directs cell activities and can be replicated to create copies of themselves and the cell in the future. You also need a membrane that isolates cell contents from the external environment. Let's examine some suggestions regarding how this may have come about. 3.1.2.3a) Replicating Molecules Today, most life uses DNA (Deoxyribose nucleic acid - Figure 7-right) to encode all the instructions for cell activities, including producing proteins that form cellular structures. DNA can only be replicated by enzymes composed of proteins. The information needed to create these enzymes is encoded in DNA. This creates a classic chicken and egg situation: You can't have the DNA without the enzymes, and you can't have enzymes without the DNA—a paradox! To circumvent this paradox, scientists have suggested that the first cells on Earth did not use DNA but a similar yet simpler molecule called RNA (Ribose Nucleic Acid - Figure 12-left). Both RNA, like DNA, are composed of units called nucleotides comprising a photoshate, a sugar and a base. In DNA, the sugar is deoxyribose, while in RNA, ribose is used. The bases (which form the "letters" in the genetic code) are G, U, A, and C in RNA (each letter representing a different type of base), but in DNA, U is replaced by T. In addition, RNA is composed of a single strand, unlike the double helix of DNA (Figure 12-right). Another important difference between DNA and RNA is that RNA can replicate itself without the aid of specialized enzymes. It can also fold itself into various shapes and engage in activities that resemble metabolism. This has led to the development of the RNA world hypothesis, which suggests that one of the first and probably most significant steps towards the evolution of life is closely associated with https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 12/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System RNA. Please watch and make notes on THIS (https://www.youtube.com/watch?v=K1xnYFCZ9Yg) video about RNA world. NOTE—this video is considered examinable material! Figure 12: RNA and DNA Note: you are not required to know the details of this figure beyond that mentioned in the text of this Topic So, given that the RNA world hypothesis allows for the emergence of self-replicating molecules that can undergo evolution through natural selection and demonstrate some metabolic processes, do we have life? Not yet. Under our definition, we need to have those molecules separated from the external environment by a membrane and demonstrate the ability to regulate their internal environment in some manner (homeostasis). 3.1.2.3b) Cell Membranes The development of cell membranes was a crucial step in the evolution of life. Membranes allow beneficial molecules to be concentrated, increasing the likelihood of interesting chemical reactions. They also isolate the cell's contents from the external environment, creating a more stable internal environment (homeostasis). Cell membranes are primarily composed of layers of fatty acids (Figure 13-top-right). Fatty acids are lipid molecules with water-loving (hydrophilic) heads and water-hating (hydrophobic) tails. In water, they spontaneously form bilayers (Figure 13-bottom) with tails facing inward and heads facing outward. These bilayers can also form spheres called liposomes (Figure 13-right), which have hydrophobic heads both on the outside and inside, surrounding a central water-filled cavity. While liposomes are not cells, they demonstrate the potential of fatty acid bilayers to concentrate organic molecules, including RNA. This might have been a mechanism that contributed to the formation of "protocells," early precursors of cellular life. However, cellular membranes are more complex structures that, in addition to lipid bilayers, have evolved sophisticated machinery to facilitate transport between the cell and its surroundings. https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 13/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System Figure 13: Fatty Acids, a Bilayer Sheet and a Liposome. LadyofHats, CC0, via Wikimedia Commons 3.1.2.4 Where Did Life Emerge? The question of where life originated is a fascinating one, and many different environments have been proposed. Darwin suggested a "warm little pond" rich in organic molecules, while others favour locations like tide pools, hot springs, and hydrothermal vents. For this discussion, we'll focus on alkaline, off-axis hydrothermal vents, which possess several intriguing characteristics that may shed light on the origins of life. 3.1.2.4a) Organic Molecules and Catalysts The alkaline fluid flowing through these off-axis vents moves much slower than the acidic, superheated water of black smokers. Instead of flowing through a large chimney-like structure, the water percolates through a network of tiny interconnected pores ranging from micrometres to millimetres. The slower flow rate in this system allows any organic molecules that form to reside there for longer periods, increasing their concentration and enabling more complex reactions. Additionally, the longevity of these alkaline vent systems, often exceeding 100,000 years, makes them more favourable candidates for the origin of life compared to black smokers, which tend to collapse within a few decades. It's important to remember that the alkaline vents of the distant past were not identical to those we observe today. Over 4 billion years ago, the oceans lacked dissolved oxygen and contained much https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 14/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System higher concentrations of dissolved (ferrous) iron. The higher levels of atmospheric CO2 (10-40% of atmospheric gases, compared to 0.4% today) would have allowed more CO2 to dissolve in the oceans. This CO2 would react with water to form carbonic acid, making the oceans more acidic with a pH of 5-7 compared to today's 8.1. These conditions would have promoted the precipitation of iron hydroxides and sulphides rather than iron oxides on the walls of the vent pores. This is significant because iron sulphides, along with other metals like nickel and molybdenum, are essential components of catalytic molecules found in enzymes today. 3.1.2.4b) Metabolism and Cell Membranes To understand how alkaline vent systems might explain the development of cellular metabolism, let's examine how our cells' powerhouses, mitochondria (Figure 14-left), utilize hydrogen as an energy source. Mitochondria have two membranes. Protons (positively charged hydrogen atoms) are actively pumped across the inner membrane into the space between the inner and outer membranes. This creates a concentration gradient, with a higher concentration of protons outside the inner membrane. Protons then flow back across the membrane (down the concentration gradient) through a specialized cellular machine called ATP synthase. As they move, they turn the ATP synthase mechanism (not unlike water moving a water wheel), generating ATP (Adenosine triphosphate), which can be used to power other cellular processes. This process is known as oxidative phosphorylation. For an animation that demonstrates this process, see HERE (https://www.youtube.com/watch?v=RDya7GGRAmg). Note: Any information in the video beyond that provided in the paragraph above is not examinable. Figure 14: Mitochondria (left); Inner and Outer membrane walls illustrating the proton pumps and ATP Synthase. Modified from Figure 4.19, Concepts of Biology - 1st Canadian Edition by Charles Molnar and Jane Gair is licensed under a Creative Commons Attribution 4.0 While we won't delve into the chemistry in detail, it's important to note that the difference in acidity (proton concentration) between the alkaline vent fluids and the surrounding environment creates a proton gradient similar to the one found in mitochondria (Figure 15). It's possible that organic materials evolving within these vents could have harnessed this natural flow of protons as an energy https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 15/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System source to drive chemical reactions. Additionally, experiments have shown that the micropores in these vents and their associated chemical reactions can generate fatty acids, which could have formed the first cell membranes, further isolating and concentrating cellular contents. Over time, with the development of more sophisticated membranes and cellular machinery, life may have learned to create its own proton gradient without relying on the vents, enabling it to venture out and populate the oceans. In essence, the pores in hydrothermal vents might have served as templates for the earliest cells. Figure 15: Proton gradient in a Hadean alkaline vent system 9 (left), Modern Alkaline Vent System (right) Early evolution without a tree of life, June 2011Biology Direct 6(1):36, DOI:10.1186/1745-6150-6-36, SourcePubMed, LicenseCC BY 2.0 3.1.2.4c) Evidence from LUCA LUCA, an acronym for the Last Universal Common Ancestor, is the common ancestor of all life on Earth today (Figure 16). By studying the genomes of all living organisms, scientists have determined that this ancestor lies at the branching point between archaea and bacteria, with eukaryotes evolving later along the archaea branch. To make this determination, scientists identified the oldest genes shared by all life, which LUCA must have also possessed. This analysis reveals that LUCA had genes involved in metabolizing hydrogen and carbon dioxide, and that metals like iron, nickel, and molybdenum were crucial for these processes. All of these elements could have been found in alkaline vent systems. While this is not conclusive evidence for the nature and origin of the first life form, it certainly sheds light on the characteristics of these ancient microbes and supports the off-axis hypothesis. https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 16/17 12/13/24, 1:07 PM Unit 7 Topic 3.1 Early Origins: EOSC_V 310 99A 2024W1 The Earth and the Solar System Figure 16: The three domains of life and LUCA Chiswick Chap, CC BY-SA 4.0 , via Wikimedia Commons 3.1.3 Summary So what did we cover in this topic? We considered possible origins of the non-living Earth Systems We described life and its characteristics. We considered the origin of life's building blocks (extraterrestrial, atmosphere, hydrothermal vents). We described a possible origin of cells, particularly replicating molecules and cell membranes. We reviewed the evidence that suggests alkaline hydrothermal vents may have been the environment in which life evolved. Required Additional Materials See the link at the top of this page above "Notes." DO NOT TAKE THE QUIZ TILL YOU HAVE READ ALL THE ARTICLES FROM ALL THE TOPICS IN UNIT 7 https://canvas.ubc.ca/courses/148569/pages/unit-7-topic-3-dot-1-early-origins?module_item_id=7219925 17/17