Planet Earth

Planet Earth - Planet Earth:1 Planet Earth Formation Ocean,...

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Planet Earth:1 Planet Earth Formation Ocean, Atmosphere, Life Interior Age of Earth Formation Last time we looked at the formation of the universe and got to the creation of galaxies and our solar system. Recall that a disk of spinning interstellar dust turned into our solar system about 4.6 billion years ago. Most of it concentrated in the center, making the sun, and most of the rest became the planets. Of this dust, most is hydrogen, deuterium, and helium, made during the Big Bang and the rest is all of the other elements, made in the explosions of massive stars. Well, one of the planets became our Earth, so let’s concentrate on this planet today. As some of the dust coalesced, forming Earth, three parts developed. In the center is the core , outside that is the mantle , and there is a thin skin, called the crust . We’ll get to the details later. As Earth was forming, the heavier elements, mostly iron and nickel, concentrated in the center, forming the core. The lighter elements formed the mantle, mostly molten in the early days. A thin scum at the surface of the mantle cooled and became the crust. As this crust went through cycles of melting and cooling, the lighter elements in it rose to the surface and congealed into the continental crust, which now is very different than the crust of the ocean basins. While Earth was very young, a small planet collided with it. This jolt caused the mantle of the smaller one to shoot out, possibly taking some of Earth’s mantle with it. Its core joined up with Earth, ending up as part of Earth’s core. The mantle that shot off formed our moon, and continues to rotate around our planet. (This is the leading theory for the formation of the moon, but it is far from certain.) Ocean, Atmosphere & Life Early on, the ocean and atmosphere started forming. The early mantle may have been 10 to 20% water, which escaped as the mantle material melted. There may have been a true ocean by four billion years ago. The first atmosphere was made up of nitrogen, hydrogen sulfide and carbon dioxide, which also were supplied by the mantle. Atmospheric oxygen was not present at first, but showed up later: some from the breakdown of water and most from photosynthesis after it developed. Now, the atmosphere is about 78% nitrogen, 21% oxygen and 1% other gases—very different than in the beginning.
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Planet Earth:2 And where did life come from? The correct scientific answer is ‘we don’t know.’ Somehow, chemical changes brought about simple amino acids and these changed over time into proteins. These somehow developed DNA and RNA and started replicating themselves. Experiments have shown that amino acids can be formed by taking a chemical mix similar to what existed in the early oceans and zapping it with electricity, simulating lightning. Another theory is that these complex molecules arrived in comets or meteorites. The chemistry at deep ocean hot springs is about right to make up DNA and RNA, so that is one possibility for that part of the problem. Anyway, somehow single celled
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This document was uploaded on 10/27/2011 for the course GEOG 1401 at Texas Tech.

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Planet Earth - Planet Earth:1 Planet Earth Formation Ocean,...

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