Earth formation and composition

Question 1

Ancient plate movement and environmental history of the earth

Answer 1

Pangea: 255 million years ago

Last Glacial Maximum: 18,000 years ago

Question 2

The Big Bang Theory

Answer 2

13,.7 billion years ago

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

Question 3

Light elements that form in first 3 minutes of big bang

Answer 3

• hydrogen
• Deuterium: protons and neutrons collide
• Helium: deuterium atoms collide

Question 4

Re-ionisation

Answer 4

• 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

Question 5

Supernovae release

Answer 5

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

Question 6

larger stars

Answer 6

live fast, die young

Question 7

Stars (8 times size of sun)

Answer 7

• last about 10 million years

- expand into red giant and explode in supernova

Question 8

How and when did our solar system form?

Answer 8

4. 6 billion years ago, hot explosion, still expanding

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

Question 9

The sun forms

Answer 9

• 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

Question 10

Sun history

Answer 10

• 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

Question 11

Meteorites

Answer 11

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

Question 12

Iron meteorites

Answer 12

almost completely metal (cores of asteroids)

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

Question 13

Stony-iron meteorites

Answer 13

nearly equal amounts of metal and silicate crystals

Question 14

stony meteorites

Answer 14

dominated by silicate minerals

Question 15

Chondrites

Answer 15

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

Question 16

Achondrites

Answer 16

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

Question 17

Inner planets

Answer 17

• 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

Question 18

Giant outer planets

Answer 18

• 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

Question 19

formation of the moon

Answer 19

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

Question 20

differentiation

Answer 20

• 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

Question 21

differentiation of interior into concentric layers

Answer 21

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

Question 22

A radioactive earth

Answer 22

• 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

Question 23

Plate tectonics

Answer 23

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

Question 24

Formation of the crust

- Lighter elements concentrated towards the surface

Answer 24

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

Question 25

Composition of the crust

- Denser Elements

Answer 25

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

Question 26

Summary

Answer 26

• 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