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ESS102H1 (104)

Lecture 4

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University of Toronto St. George
Earth Sciences
Christine Burton

Formation and evolution of the universe - Currently it is thought that expansion started with a cataclysmic explosion J Big Bang J between 10-20 billion years ago - The further away the galaxy is, the faster it is retreating J 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 d
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