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Dynamic Earth > Earth formation and composition > Flashcards

Earth formation and composition Flashcards

1
Q

Ancient plate movement and environmental history of the earth

A

Pangea: 255 million years ago

Last Glacial Maximum: 18,000 years ago

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2
Q

The Big Bang Theory

A

13,.7 billion years ago

  • very hot, very dense point in space
  • inflation to expansion
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3
Q

Light elements that form in first 3 minutes of big bang

A
  • hydrogen
  • Deuterium: protons and neutrons collide
  • Helium: deuterium atoms collide
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4
Q

Re-ionisation

A
  • clumps of gas collapse form the very first stars and galaxies
  • stellar nucelosynthesis forms elements up to iron as stars ran out of H and expand to red giants
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5
Q

Supernovae release

A
  • very large amounts of energy
  • neutrons, allow heavier elements (uranium/gold) to be produced.
  • these elements expelled out into space
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6
Q

larger stars

A

live fast, die young

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7
Q

Stars (8 times size of sun)

A
  • last about 10 million years

- expand into red giant and explode in supernova

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8
Q

How and when did our solar system form?

A
  1. 6 billion years ago, hot explosion, still expanding

- meteorites are remnants of the early solar system and can be dated back

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9
Q

The sun forms

A
  • gravitational condensation
  • rise in temperature (millions of degrees)
  • nuclear fusion begins after 50 million years
  • sun fairly dim before fusion started
  • H+H = He (some mass converted to solar energy
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10
Q

Sun history

A
  • presence of elements heavier than helium indicate previous supernova
  • heavier elements formed in previous star formation and death
  • our sun forms helium by nuclear fusion
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11
Q

Meteorites

A
  • remnants form formation of solar system (date back 4.6 billion years ago)
  • a few from the moon and mars
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12
Q

Iron meteorites

A

almost completely metal (cores of asteroids)

- thought to be cores of asteroids that melted early in their history

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13
Q

Stony-iron meteorites

A

nearly equal amounts of metal and silicate crystals

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14
Q

stony meteorites

A

dominated by silicate minerals

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15
Q

Chondrites

A

have never significantly melted and have compositions similar to the sun and the solar system as a whole

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16
Q

Achondrites

A

have melted and are similar to igneous rocks on earth. these include rocks from mars and the moon as well as from melted asteroids.
- have been changed by melting and crystallisation

17
Q

Inner planets

A
  • terrestrial planets
  • composed of rocks (silicate based) and metals
  • volatile (H, He and water) were blown away when sun ignited
  • Fe and Si are abundant
18
Q

Giant outer planets

A
  • most volatiles swept from close to sun ended up in the cold outer reaches of the solar system
  • rocky cores but mostly made of H and He
  • Pluto (and charon) are odd + part of Oort Cloud
19
Q

formation of the moon

A
  • collision of earth with mars sized body
  • occurred at about 4.5 billion years ago
  • around 20 million years after earth formed
20
Q

differentiation

A
  • early earth was hot(lots f radioactive elements)
  • dense elements sank to the centre (formed the core)
  • lighter materials rose towards the surface
  • gases/volatiles from interior
21
Q

differentiation of interior into concentric layers

A
  • densest at centre
  • solid iron outer core
  • liquid iron outer core (magnetic field)
  • mantle (bulk of volume)
  • crust (0-40km veneer)
22
Q

A radioactive earth

A
  • elements such as uranium and thorium would have been far more abundant on the early earth.
  • radio active decay gives off heat
  • today most of earths internal heat is generated from the breakdown of potassium to argon
23
Q

Plate tectonics

A

mantle convection drives plate motion

  • divergent boundaries: ocean ridges, seafloor spreading, rifts
  • convergent boundaries: subduction Zones
  • transform fault boundaries: strike-slip faults
  • materials are constantly (but slowly) recycled
24
Q

Formation of the crust

- Lighter elements concentrated towards the surface

A
  • Si, Na, K form minerals such as quartz, orthoclase feldspar etc.
  • crystallise at 800oC
  • form early continental crust. difficult to subduct
25
Q

Composition of the crust

- Denser Elements

A
  • Mg, Fe etc. form minerals such as pyroxenes, olivine
  • crystallise at 1100oC
  • form upper mantle and ocean crust. subduct more readily
26
Q

Summary

A
  • the solar system is much younger than the universe
  • the earth is dived into core, mantle, ocean and continental crust (each has its own chemistry, density, heat capacity etc.)
  • plate tectonics means that materials are constant recycled

Dynamic Earth (10 decks)

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