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Lecture

Lecture 4


Department
Earth Sciences
Course Code
ESS102H1
Professor
Christine Burton

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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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