EAS 206 Quiz 1 (Earth)

Law of original horizontality

Sedimentary rock layers are deposited horizontally and the layers are continuous

Law of superstition

In a sequence of sedentary rock, each layer is older than the layer above it and younger than the layer below it

• applicable to rock layers deposited at the surface (sedimentary rock, lava flows, ash layers)

Law of cross-cutting relationships

If a fault or body of rock cuts through another body of rock, fault must be younger than the rock which it cuts through

Law of inclusions

One rock included in another rock older than the rock that includes it

Mantle

• Upper and lower sections

• Includes the asthenosphere

• Iron and magnesium (olivine) minerals

Core

• Mostly iron metal (very dense)

• Solid inner, liquid outer

Asthenosphere

• top part of the upper mantle (10 – 250 km)

• it is weak (plastic, able to flow)

• partly molten (close to its melting point)

source of magma

Molten rock ascends into crust, may erupt on surface (volcanic activity)

Lithosphere

• includes the rigid part of the mantle and the overlying crust

• Ten to several hundred km thick, rides on plastic asthenosphere (plate tectonic movement)

How do we know the composition of the Earth?

1. Density - water has to be less dense than the interior to float

2. Seismic - Velocities of waves change depending on rigidity and density, In a liquid, S waves are not transmitted but P waves are

3. Meteorites - Iron meteorites thought to represent fragments of the core of a now-disrupted planetary body, Stony meteorites thought to represent mantle of that body

Tectonic convergent margin forms

Mountains, Faults, metamorphic and igneous rocks, folding

Tectonic divergent margin forms

Faulting from volcanoes

Hadean

• Accretion of millions of planetesimals in a short time

• Hot

• Differentiation of iron to core, silicates to mantle, and gases to atmosphere

• Probable magma ocean

• Moon-forming event

• Heavy bombardment

Archean

• formation of continental nuclei, assembly of shields

• Cooling off

• Condensation of oceans, removal of water vapour

• Origin of primitive life, production of oxygen

Proterozoic

• Stabilization of continents

• Sedimentary platforms

• Stronger, thicker lithosphere

• Towards modern plate tectonics

• Removal of CO2

• Increase of O2 – Banded iron formation

Phanerozoic

• Deposition of sedimentary rocks on continents

• Extensive expansion of life in oceans, onto land

• Grouping of plates into Pangea, and breakup

• Glaciation

What was the Earth like about 4 billion years ago?

• iron rich seas (water could condense) covering 90% of Earths surface

• CO2 rich atmosphere

• Over 93 degrees celsius

• Volcanic island chains

Evidence of life if looking down on Earth from space

• Coral reefs

• Ozone

• Oxygen

• Human activity

Galaxy supercluster

tightly packed chains and sheets of galaxies

Fusion

combination of two or more nuclei to form a different, heavier, element; the by-product is radiation (including light and heat that we require to live)

• form elements in stars (hydrogen → helium)

What keeps a star together?

• Are dense and feel their own self-gravity

• Gravity attempts to cause collapse but high gas pressure can oppose gravity

• High temperatures create high pressures

Hydrostatic Equilibrium

For a stable equilibrium:

• If you squash a star, it must get hotter/higher pressure faster than gravity gets stronger

• This causes it to bounce back to the equilibrium position

End of core Hydrogen burning

hydrogen in the core is used up and core loses pressure and collapses (moves the star away from the Main Sequence)

Low Mass Stars

• Evolution is slow

• At each stage, the star changes dramatically

• helium core collapses and gets hotter slowing its collapse

• shell of burning hydrogen around the hotter helium core, making the hydrogen shell burn faster

• hot, high pressure shell makes the outer part of the star expand, puffs up to a Red Giant

High Mass Stars

• Evolution is rapid

• Stages blur together

• undergo less dramatic luminosity changes as burning changes

• At more than 8 solar masses the star will get hot enough to burn Carbon

• Massive stars transition to burning new elements smoothly

• core becomes hotter to fuse heavier and heavier elements

• core is surrounded by many shells burning the lighter elements

Supernova

• cataclysmic explosion of a star, as a result of internal nuclear reactions

• Fe does not “burn”, star contracts

• Outer shells of unburned fuel react suddenly, star explodes, spreading elements into space

• Gives off vast amounts of light in just a few weeks

• Iron core can’t produce energy

• Fusion reactions still occur but these use up energy (to make heavier elements)

Nebula

dusty, dense cloud

Gravitational collapse

when molecules are concentrated, attracted to each other

– May be triggered by nearby supernova

Evidence for the formation of the Solar System

1. Astronomical observations show us the sequence of events (collapse → T Tauri stage with disk → clearing of dust)

2. Meteorite studies provide the details – Processes within the solar nebula/disk, accretion, Age and timing

Orbits

Shows solar system was formed from a rotating disk of dust and gas

T Tauri stars

stars that are similar in mass to the Sun, but only about 1 million years old

Proplyds

disks of dust and gas around young stars; contraction of “protoplanetary disks”

Refractory materials

Materials that form solids at very high temperatures

• e.g., calcium-aluminum oxides

Volatile materials

materials that condense/solidify at very low temperatures

• e.g., ices

Meteorite

extraterrestrial rock that has fallen through our atmosphere, from asteroid belt, provides evidence for billions of many generations of stars through pre-solar grains

Carbonaceous chondrites

• one type of meteorite

• derived from asteroids in the asteroid belt

• preserve a record of processes happening in the solar nebula/disk

• Contains carbon and volatile elements

• Evidence for supernova collapse

Chondrules

Carbonaceous chondrites in Meteorites, spherical objects made of silicate minerals, formed by melting and cooling of droplets in the solar nebula, related to the T tauri stage

Matrix

Carbonaceous chondrites in Meteorites, very fine dust, preserves nebular dust, material from before collapse

Pre-solar grains

Carbonaceous chondrites in Meteorites, silicon carbide, diamond, formed from supernovae, solids from pre-existing stars and supernovae triggering collapse

Radioactive elements

Carbonaceous chondrites in Meteorites, U within minerals, ages the solar system as 4.567 ± 0.0001 by a

CAIs

Carbonaceous chondrites in Meteorites, formed in high heat, calcium-aluminum inclusions; made of refractory minerals, first solids formed by condensation in our solar system; provide age for the beginning

Formation of planets

1. Slowly rotating portion of a large nebula becomes a globule as a mostly gaseous cloud collapses by gravitational attraction triggered by supernovae

2. Rotation of cloud prevents collapse of the equatorial disk while a dense central mass forms

3. Protostar ignites - warms the nebula vaporizing dust exposing the star and creating bipolar outflows (T tauri stage), then cools forming grains in the central plane

4. Nebula clears - star energized by fusion and cold bodies (planets) remain, happens 10ma after collapse

Planetesimals

• small solid bodies that form planets

• formed from grain-to-grain accretion of dust

• Many collisions between them

Differentiation

separation of materials in a planetary body according to density and chemical affinity

• Converts homogeneous body to layered body

• Requires planetary heat

• Must be able to flow (like the asthenosphere)

Minerals in the core

Metallic - iron, nickel, sulfur

Minerals in the mantle and the crust

Silicate - magnesium, iron, calcium, sodium, potassium

How planets generate heat

• Accretionary

• Core formation

• Radiogenic

• Solar Energy

• Tidal

Accretionary Heat

Heat that comes from the conversion of kinetic energy, heat is trapped inside the planet if accretion is rapid, important heat source in the formation of the solar system

Heat from Core Formation

Converts gravitational potential energy to heat as molten iron drops to the centre of a planet, important heat source in the formation of the solar system

Radiogenic Heat

Caused by the decay of radioactive atoms (uranium, thorium, potassium) dispersed in the interior of the planet, important through out the whole life of the solar system

Solar energy/radiation

Produced by nuclear fusion in a star and is transmitted to planets in electromagnetic waves, important through out the whole life of the solar system

Tidal heating

Results when a satellite (ex. moon) is repeatedly flexed by gravitational attraction, not a significant source of heat

Three ways heat is transferred between planets

Conduction, Convection, Radiation, smaller planets lose heat faster

Conduction

vibrational energy of an atom is transferred to adjacent atoms, within the mantle and through crust via magma

Convection

warm material expands and moves upwards, displacing cooler and denser material downward, through crust (soil)

Radiation

emission of electromagnetic waves from a hot body’s surface to its surroundings, heat transferred in space

Impact Cratering role in Earth’s history

Formation of the Moon, K/T mass extinction, creates craters on Earth

bolide/impactor

meteorite or comet

3 Stages of the Impact Cratering Process

1. Compression

2. Excavation

3. Modification

(Typically vaporized/ destroyed in the impact event, uses the law cross-cutting relationships (crater must be younger than the surrounding rock))

Whitecourt Meteorite Impact Crater

youngest and best-preserved crater in Canada, and the only crater in Canada with associated meteorites, low-energy event (Bolide not totally vaporized in the impact; meteorites are samples of the bolide)

Bolide features

• Ejecta blanket, (sometimes) rays

• Overturned rim

• Impact melt sheet

• (sometimes) Central uplift (peaks or rings)

• Breccia (shattered rocks)

• Tektites (molten droplets in the crater)

Compression Stage (Impact Cratering Process)

• Shock wave expands out from point of impact

• Compresses rock to 1/3 its usual volume

• Rock can flow like a fluid

Excavation Stage (Impact Cratering Process)

• Decompression wave follows the advancing shock front

• Target rock and bolide (now vaporized) flow, spray out of the transient cavity

• Ejecta travels out as conical sheet

• Crater rim overturned

Modification Stage (Impact Cratering Process)

• Typical for large structures

• Gravity unable to sustain the cavity

• Slumping of crater walls

• Central uplift

• Continues indefinitely