Formation - GEOL 114 The Earth's Dynamic Interior Lecture...

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GEOL 114 The Earth's Dynamic Interior Lecture Notes (Copyright © 2006 by Jeffrey S. Barker) 5. Formation of the Planets and Earth Nucleosynthesis We now know something of the physical structure of the Earth as a whole. Now it is time to consider what the Earth is composed of. We are going to discuss a number of chemical compounds and how they got to be where they are in the Earth. But first, how did these compounds get to Earth in the first place? To answer this, we must step way back in space and time and consider the life cycles of stars. Originally (whatever that means), immediately after the "Big Bang", all that existed was a hot soup of sub-atomic particles (quarks). As seconds passed and temperature decreased, protons and neutrons could form. These would later attract electrons to become hydrogen and helium atoms (with proportions probably about 75% H and 25% He). When particles of this interstellar gas collide, they are held together by their mutual gravity. Since the total gravity of these stuck-together particles is greater, additional particles are more easily attracted. This accumulation of material is called accretion . As mass increases, gravity increases, and the mass is pulled more strongly toward the center. This self-gravitational contraction results in heating (due to conservation of energy). Extra Info Extra Info : Examples: a tire pump gets hot, partly by friction, but also partly due to the compression of the air. Also, although "hot air rises", the temperature of the upper atmosphere is quite cold, due to low pressure. GEOL 114 1 5. Formation of the Planets and Earth
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Once the pressure and temperature exceed critical levels, a nuclear fusion reaction occurs. The Hubble Space Telescope has imaged a region in which astronomers believe this process is occurring. The reaction that occurs in nuclear power plants is called fission , or "atom splitting". This results from the spontaneous decomposition of unstable atoms (such as uranium) to more stable atoms (such as rubidium and lead). The alternative is called fusion , in which low atomic mass nuclei are joined ("fused") to generate a larger atomic mass nucleus. When the pressure and temperature within our interstellar cloud reach a certain level ( T 20Million 0 C ), a fusion reaction called hydrogen burning occurs. Extra Info Extra Info : When we talk about nuclear reactions, we refer to the mass number, the sum of protons and neutrons in the nucleus, as a superscript before the symbol of the element (e.g. 4 He). If the number of protons changes, we change the name of the element (e.g. 5 Li), however different numbers of neutrons create different isotopes of the same element (e.g. 3
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Formation - GEOL 114 The Earth's Dynamic Interior Lecture...

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