Formation of Earth

• The Earth's structure includes the early geosphere, atmosphere, and hydrosphere.

Planetesimal Accretion Theory

• Accretion theory explains how the solar system and Earth's layers formed.
• 4.56 billion years ago, an interstellar cloud of gas and dust (solar nebula) formed the sun and planets.
• Accretion is the gathering of smaller pieces/formations.
• A distant supernova caused shockwaves in the solar nebula, concentrating material and forming the center of the sun.
• Leftover material, the future planetesimals, orbited the sun.
• Collisions occurred which leads to GPE converts to heat energy and gain mass.
• The process continued and planetesimals were created.

The Accretion Phase

• By the end of the accretion phase, all main eight planets were formed.
• Gravitational pull formed moons from planetesimals and flung some into space or near misses.
• Radiated heat caused dense metals to sink to the core where lighter materials created the mantle and solidified.
• Earth's water and atmosphere came from icy comets and planetesimals mixed with the mantle materials through volcanic activity and impacts.

Timeline

• The Earth's surface cooled to form its first crust and the mantle began to solidify between 4-4.4 billion years ago, which resulted in inorganic spheres.
• By 4 billion years ago, the crust stabilized, which allowed Earth's surface to cool which resulted it permanent oceans.
• Earliest signs of life appeared around 3.8 billion years ago.

Earth's Inorganic Spheres (HAG)

• HAG formed between 4 - 4.4 billion years ago.
• HAG Includes the Hydrosphere, Atmosphere, and Geosphere.

Differentiation Definition

• Initially, Earth consisted of mixed metals and silicates then underwent differentiation.
• Differentiation is the separation of original planetary material into layers based on density; most materials must be liquid/molten.
• Typically, the layers: iron/nickel at the bottom, dense rocks like peridotite in the middle, light rocks like basalt and granite at the top.
• Layers solidified as the planet cooled, preserving the differentiation.

Big Bang Theory (Just in case)

• The Big Bang theory explains the start of the Universe.
• This occurred 13.77 billion years ago.
• The Big Bang singularity had infinite density, creating a gravitational field.
• Quarks and electrons formed matter in the early Universe.

Geosphere Layers

• The geosphere (IOS M) includes all materials below the Earth's solid surface.
• The three layers are a thin silicate crust, a thick silicate mantle and a metallic iron core.
• The geosphere includes the following elements (top 4): Iron(32.1%), Oxygen(30.1%), Silicon(15.1%) and Magnesium(13.9%)
• 99.7% of Earths mass
• Geosphere boundary covers from 0-6000km

Crust (OS)

• Includes the elements Oxygen (46.6%) and Silicon (27.7%)
• It is 0-100km thick with a temperatures of 15° (top) to 500°C (base)
• The outermost layer of Earth with a mass of 5.97 x 10^21 tonnes

Mantle (OMS)

• Includes the elements Oxygen (44.8%), Magnesium (22.8%), and Silicon (21.5%)
• Is 2900km thick (mantle-core boundary) and the temperature ranges from 500 - 3750°C
• Mantle is low-density crystalline magnesium iron silicates in the upper mantle and high-density the lower mantle.

Core (IS N)

• Includes the elements Iron (85.5%), Silicon (6%), and Nickel (5.2%)
• Is 3500km thick with temeratures of 3700°C degrees (Outer core) and 5000°C (Inner core)
• The inner core is 99% Earth's iron.
• The core began solidifying 1 billion years ago.
• Convection currents in the liquid outer core cause earth's magnetic field
• The outer core is liquid and the Inner core is solid due to extreme pressure

Atmosphere

• It is the blanket of gases surrounding Earth or any other celestial body.
• Cold air may contain almost no water vapor but hot air contains up to 4% water vapor.
• Free oxygen is singular and not covalently bonded to other atoms.
• Volcanoes mainly produce H20, N, CO2.
• No free oxygen initially because it was combined with other elements in an anaerobic environment.
• Two processes added oxygen to the atmosphere, photosynthesis and photolysis.
• Photolysis is when ultra violet rays cause split of water vapor atom to free oxygen.

Earth Timeline

• 4-4.4 billion years ago, Earth's surface cooled, which led to first crust and allowing mantle to solidify.
• 4 billion years ago, the crust stabilized, which allowed Earth's surface to cool enough that allows permanent oceans to form.
• Earliest signs of life date back 3.8 bullion years ago

Hydrosphere

• The hydrosphere is water present on Earth.
• 96.5% of Earth's water is in oceans.
• Without water, Earth would be a barren sandy dust place without plate tectonics.

Determining Earth Structure

• Avg. density of each layer
• Failed atttempts to only dig 10-12km below the surface of the earth b/c drill bits start to disintegrate at 350°C with atmospheric pressure of 40,000.
• Rocks often ejected from the upper mantle through tectonic and volcanic action or xenoliths, allowing scientists to judge internal structures.

Seismic Waves

• P-waves are longitudinal, and travel 8km/s in the upper mantle and 6km/s in the lower crust. P-Waves refract and are faster in the earth.
• S-waves are transverse, and they travel N/A km/s in both the upper mantle and lower crust. S-waves refract both but are slower.

Seismic Wave Use

• Seismic waves help determine boundaries between Earth's layers.
• Seismometers measures ground movement.
• Pickup of seismic waves from earthquakes happens through seismometer
• Can determine distance to ruptured fault by difference in the arrest times between waves

Evidence

• S-waves provided evidence for liquid outer core because of reflecting back
• There are different materials in the Earth's compositional layers.
• Analysis of seismic wave data helps to understand reflecting and refracting in various mediums

Moho

• The Moho distinguishes the crust from the mantle
• The Moho was discovered in 1909.
• Andrija Mohorovicic used an earthquake that produced two almost identical p-waves.
• one of the p waves travelled was travelling at 6km/s while the other travelled at 8km/s

Deductions

• Slower 6km/s wave moved through less dense crust while the faster 8km/s wave moved through the mantle.
• Seismic waves inherently curved.
• Able to calculate the depth of the crust with distance to the crossover point; greater distance means deeper crust.
• Moho discontinuity separates the these waves, distinguishing upper/lower crust.

Peridotites

• Green rock composed of magnesium and iron silicates that forms 60km below Earth's surface
• The speed of p-waves in peridotites is like those below the Moho boundary.
• Scientists believe there is peridotite below the Moho boundary, and they named it mantle peridotite.
• Average density in the mantle is .3gm cm-3, for the earth it is 5.6 gm cm-3 and for crust it is 2.6 gm cm-3
• The materials become denser when you go further into the earth such as the core

Seismic Shadow Zones

• In 1936 Inge Lehmann discovered weak p-waves in shadow zones.
• She thought the p-waves were being reflected by a very dense medium which she deduced must be the inner core.
• The s wave shadow zone is from 103° of the earthquake's epicenter.
• The p wave shadow zone is from 103° to 143°.

Testing of atomic bomb to fact check Lehmann's theory

• In Nevada, scientists tested a theory about a solid core by detonating an atomic bomb.
• Scientists found that some of the p-waves were reflected back after detonation.
• Result indicate significant changes in material and a denser liquid outer core.
• P waves can change direction or be reflected if they encounter a rapid change in mediums

Location and base of the lithosphere

• Consists of different layers
• Crust is less dense on the surface 0-50km
• Lithosphere = Earth's crust + brittle upper mantle, from 50-150km, P-waves speed up
• Asthenosphere the mantle is in a ductile state, P-waves slow, melts under high pressure/temps from 150-700km.
• Mesospheric mantle has high pressure, compress materials, and p-waves speed up from 700-2900km.

Seismic Tomography

• Seismic tomography uses various earthquakes to build an interpretable diagram
• Helps show various boundaries by utilizing p-wave anomalies and average speed of p-waves in each material.

Subducting Oceanic Plate

• Cold, stiff, and dense than continental.
• High p-wave anomaly
• Also shows different layers, boundaries and a p-wave speed graph

Earths Age

• Use M1.1.5 to help find more evidence on the Earths age.
• Radiometric dating can indicate earths age

Radiometric

• Isotopes release three rays: alpha, beta, and gamma
• Alpha emission decreases atomic and mass numbers by 4.
• Beta emission increases the atomic number by 1 with mass # changes
• Gamma emission has N/A changes.

Radioactivity

• Radioactivity occurs when an atom's nucleus is unstable and wants to 'spit' out protons/electrons to be stable.
• Radioactive decay is how long it takes for an element to become stable
• Isotopes change variances of elements, affecting only the # of neutrons.
• Unstable isotopes are called Radioisotopes

Half life

• The amount of time one has for a sample of atoms to decay
• Time it takes a sample to decay to new stable form.
• Every radioisotope has its own fixed half-life.
• Can be displayed with an exponential graph

Earths Age

• No exact definitive age
• At least 4.4 billion years old, through radiometric dating of rocks and zircon crystals.
• Study of Earth's age is hindered by constant geological and weathering processes.

How to Calculate Earths Age

• Rock samples from the Apollo missions during 1969-1972 provided help
• Resulting is 4.40 – 4.57 billion years old
• Meteorite evidence originated in the formation of Earth.

Meteorites

• Meteorites are just 'shooting stars', or fragments of rock which pass through and onto the Earth's surface
• They are made of material from solar systems moons, planets, asteroids, and comets (MAP C).
• Meteorites are divided into stony (94%), iron (5%), and stony-iron (1%).

Stony Meteorites

• Stony meteorites subdivided into: Chondrites (86%) Achondrites (8%).
• Provide information about the possible age and layers of Earth as it existed in the planetesimal accretion phase.
• The oldest meteorites, or Chondrite,s are 4.57 bullion years old. Used to form planetesimals (PAM) asteroids and meteorites. Most likely accreted into large planetesimals with layers, consisted of Rocky crust, Mantle and a matellic core

Achondrite meteorite

– 10 million years. Consisted of silicate material + Textures like Earths basaltic material

• Material blasted from mars or Earths surface.
• Fragment between planetesimals or asteroids.
• Some consists of curst metallic core .
• Made weapon with the evidence of alloy in the earth

Achondrite

• • Iron meteorites are composed of metallic alloys – iron + nickel, which crystallise into kamacite + taenite (kamacite - 90% iron and taenite 35-80% iron
• Forms when a core of asteroid melts during asteroid collusions (kinetics and heat) and is used to create weapons . Was much stronger and powerful at the time

Stony-Iron Meteorite

• range from 4.44-4.54 billions year old
• Includes alloys tracine kamacite
• Afe like stony meteortes but age cannot be calculates correctly

Radiometric ages for the formation of Earth's layers

• Accumulation of total earth: 4.45-4.55 million years, Earths core 4.526 billion years
• Oldest crust made from 4.35-4.0 billion years.
• All of these requires complex and analytical methods has been used to calculate

Zircon

• are the oldest crystal known. Is Australia are 4.4 billions
• Consist of acata granocriate =one of the most reliable

Silicate Mineral Properties

• Lustre refers light with glass
• All minerals on the list consists of silicate, fesic and magic.

Silicate composition

• Is any element that consists silicon (Si) an oxygen(O).
• Magnesium and iron are in brackets because these vary.

Materials

• Festic materials consists of silicon and + aluminium but is reach is potassium
• Magic consist of higher temeperyature.
• Magic an fesic are found in granite

Rocks

• Rocks are classified by a rocks structure (CRYSTAL) and Composition .
• There are 3 categories of rock. It's either igneous, Senderman, or metamorphic

Igneous Rock

• Igneous rock forms when crystal's liquid such as rock and magma cool and crystalize Different densities consist of different silica percentages
• There Are different testing methods of different rocks with different ways they react too

Rocks

• Sedimentary occurs when chemical and rock goes through weathering erosion on the surface.
• Rocks are categorized to which the size and energy is reflect in their size and is tested with their texture

Organic Sedimentary Rock

• Derive from organic marerials = mixture of oil shale clays

Metamorphic

Forms when rocks are exposed with high heat/pressure

• Layers of rocks

Practice questions

• Refer too practice questions to enhance and master skills required for tests and assignment