Title Description:
The Earth is believed to be about 4,500 million years old. Since its format...The Earth is believed to be about 4,500 million years old. Since its formation, there have been great changes both to the land the atmosphere. The early cooling caused the oceans to form and then, as life developed, the atmosphere of ammonia, carbon dioxide and methane became polluted by oxygen. The ozone layer developed and life became more complex. Eventually the atmosphere gained its current composition of around 78% nitrogen, 21% oxygen, 1% argon and small amounts of other gases such as carbon dioxide. On the land, the continents spread out from the original Pangaea super-continent. The three main rock types that exist on Earth are sedimentary, metamorphic and igneous. As life developed, carbon-chain compounds were created. Although originally associated with living things, 'organic' chemistry is now concerned with the whole range of compounds that contain chains of carbon atoms.
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