Earth formation and composition Flashcards
Ancient plate movement and environmental history of the earth
Pangea: 255 million years ago
Last Glacial Maximum: 18,000 years ago
The Big Bang Theory
13,.7 billion years ago
- very hot, very dense point in space
- inflation to expansion
Light elements that form in first 3 minutes of big bang
- hydrogen
- Deuterium: protons and neutrons collide
- Helium: deuterium atoms collide
Re-ionisation
- 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
Supernovae release
- very large amounts of energy
- neutrons, allow heavier elements (uranium/gold) to be produced.
- these elements expelled out into space
larger stars
live fast, die young
Stars (8 times size of sun)
- last about 10 million years
- expand into red giant and explode in supernova
How and when did our solar system form?
- 6 billion years ago, hot explosion, still expanding
- meteorites are remnants of the early solar system and can be dated back
The sun forms
- 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
Sun history
- 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
Meteorites
- remnants form formation of solar system (date back 4.6 billion years ago)
- a few from the moon and mars
Iron meteorites
almost completely metal (cores of asteroids)
- thought to be cores of asteroids that melted early in their history
Stony-iron meteorites
nearly equal amounts of metal and silicate crystals
stony meteorites
dominated by silicate minerals
Chondrites
have never significantly melted and have compositions similar to the sun and the solar system as a whole
Achondrites
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
Inner planets
- 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
Giant outer planets
- 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
formation of the moon
- collision of earth with mars sized body
- occurred at about 4.5 billion years ago
- around 20 million years after earth formed
differentiation
- 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
differentiation of interior into concentric layers
- densest at centre
- solid iron outer core
- liquid iron outer core (magnetic field)
- mantle (bulk of volume)
- crust (0-40km veneer)
A radioactive earth
- 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
Plate tectonics
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
Formation of the crust
- Lighter elements concentrated towards the surface
- Si, Na, K form minerals such as quartz, orthoclase feldspar etc.
- crystallise at 800oC
- form early continental crust. difficult to subduct
Composition of the crust
- Denser Elements
- Mg, Fe etc. form minerals such as pyroxenes, olivine
- crystallise at 1100oC
- form upper mantle and ocean crust. subduct more readily
Summary
- 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
