Timeline of human history - Timeline 2: 5,000,000,000 BP to Present. History of Earth. History of Life

Timeline of human history
version 2 - by Finn Sivert Nielsen

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Timeline 2 - 5,000,000,000 BP to Present
History of Earth. History of Life

Timeline 2 narrows us down to the last 5 billion years before the present, focusing on the history of the Earth only. We see the same story as in the previous timeline, but in greater detail. First, note the description of environmental conditions on Earth before the origin of life (slime): An atmosphere consisting mainly of the strong greenhouse gas methane produces red skies and hot climates. Intensive vulcanism adds carbon dioxide to the mix, increasing temperatures further. The new-formed moon orbited far closer to the Earth than today, and as a result the tides were far stronger. One hears talk of 300-meter tidal waves coursing to and fro across the oceans on a daily basis. It was out of this potent and well-mixed stew that life (slime) arose. Do not forget, however, that the stew would not have been anywhere near as well mixed without the moon. Perhaps even slime-life is not endemic to all Earth-type planets. Perhaps a moon is required also. Secondly, note the great Huronian Glaciation that covered the Earth in ice from pole to pole, perhaps for as long as 300 million years (in comparison, the partial glaciation that the Earth has recently been through lasted only 120,000 years). How does a monster glacier of this kind arise? The current theory (or at least one theory) is that a particular strain of slime-life (called cyanobacteria) evolved around 3.5 billion years ago, which was able to perform photosynthesis. Photosynthesis, as any biologist will tell you, is the process by which plants breathe in carbon dioxide and, in the presence of sunlight and water, breathe out oxygen, retaining the carbon for building their bodies, and (at a much later stage) providing the oxygen that organisms such as ourselves can breathe in, releasing carbon dioxide that the plants in turn breathe, and so on. This is all fine and dandy as long as oxygen production (by plants) and oxygen consumption (by animals, once they evolve) balance each other out. However, when the first photosynthesizing cyanobacteria started producing oxygen, animals did not even exist. Oxygen production increased without break, reacting with every particle of free iron in the oceans and forming the vast banded iron-oxide deposits that are the main sources of iron for modern industry. Once the ocean was saturated, oxygen overflowed into the atmosphere, where it reacted with methane, destroying the greenhouse effect and sending the Earth's temperature plummeting till the planet was covered by ice and only releasing it when carbon dioxide from subglacial vulcanism had accumulated sufficiently to warm the atmosphere. Note that if this theory is true, life was born into hostile conditions (e.g. atmospheric conditions), which it gradually modified to suit itself. However, as the drama of the Huronian Glaciations shows us, this modification was a slow process of trial and error rather a linear progression. No doubt the outcome was more often than not a matter of luck. Had Earth (for example) been a less volcanically active planet, it might have remained an iceball to this day. Finally, to return to the timeline, note the consecutive appearance of three supercontinents during the last 2 billion years (there may have been others before these three). A supercontinent arises when the continents, which are constantly rifting apart and drifting around, come to (temporary) rest in a single gigantic continental mass. Since meteorologists assure us that the interiors of supercontinents are typically dry and cold (cf. Tibet today), and geologists that supercontinents typically shorten coastlines and fill in shallow seas, supercontinents may at their height have strong effects on climatic and ecological conditions on Earth.