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30 Oct 2010
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Formation and evolution of the universe
- Currently it is thought that expansion started with a cataclysmic explosion t Big Bang t between
10-20 billion years ago
- The further away the galaxy is, the faster it is retreating t expanding universe
Aftermath of the big bang
- Hot cloud containing only H (98%) and He(2%)
- Gases clump into separate clouds (nebulae)
- Collapse of nebulae leads to formation of protostars
- The high pressures and temperatures reached within protostars lead to nuclear fusion processes
(fusion of hydrogen atoms to create helium atoms)
After explosion
- Most mass concentrated in centre of rotation cloud of gas and duse
- Forms proto-sun
Stars: element factories
- Fusion reactions: fusion of H to produce He until H is used up, then fusion of He to form heavier
atoms until He is consumed, and so on up to the formation of Fe in large stars (10-30 times the
mass of the sun)
- Heavier and heavier elements are formed
- When a very massive star runs out of fuel, a very energetic explosion occurs, so that elements
heavier than Fe are formed (Supernova)
- When a star dies, it sends the heavy elements into the Universe
- A subsequent generatio of stars containing a larger proportion of heavier elements forms out of
the more compositionally diverse nebulae
- Today 99% of the mass of the universe consists of H and He (only 1% is heavy elemental matter)
Our galaxy
Solar system
- Our sun and the things attracted to it by gravity
- Probably evolved from nova explosion of a red giant about 4.6 bya
- Creates cloud of gas and dust
- Crab nebula
Formation of our solar system
- The sun is a third- or fourth- generation star
- Planets developed from the residual ring of dust and gas (protoplanetary/solar nebula)
- Dust crashing together to form planets
- Gravitational attraction of larger particles on smaller ones forms planetisimals
- Planetisimals combine to form planets of our solar system
- Nebula theory of planet formation:
o The gas and dust from the protoplanetary nebula condensed into planetesimals that
then clumped together to form protoplanets, and eventually true planets
*explain the formation of the earth starting from the big bang
- the universe > galaxy > solar system > planets
How old?
- Oldest rocks on earth are 4.28bya
The hadean eon: hell on earth (4.6 to 3.8 bya)
- No rocks from the early history of the planet survived
- No atmosphere, no oceans, just molten rock
- Very hot
- Acasta gneiss is not the oldest rock now
www.notesolution.com
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Document Summary

Currently it is thought that expansion started with a cataclysmic explosion j big bang j between. The further away the galaxy is, the faster it is retreating j expanding universe. Hot cloud containing only h (98%) and he(2%) Collapse of nebulae leads to formation of protostars. The high pressures and temperatures reached within protostars lead to nuclear fusion processes (fusion of hydrogen atoms to create helium atoms) Most mass concentrated in centre of rotation cloud of gas and duse. When a very massive star runs out of fuel, a very energetic explosion occurs, so that elements heavier than fe are formed (supernova) When a star dies, it sends the heavy elements into the universe. A subsequent generatio of stars containing a larger proportion of heavier elements forms out of the more compositionally diverse nebulae. Today 99% of the mass of the universe consists of h and he (only 1% is heavy elemental matter)

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