Since Earth was created 4.54 billion years ago the first eon (period of time in geochronology depicting half a billion years or more) in the Earth's history is called the Hadean eon which lasted for until the Archean eon which began 3.8 billion years ago and spanned for 1.5 billion years according to International Stratigraphic Chart, 2009. Hadean time is not a geological period as such. No rocks on the Earth are this old, except for meteorites. During Hadean time, the Solar System was forming, probably within a large cloud of gas and dust around the sun, called an accretion disc. The relative abundance of heavier elements in the Solar System suggests that this gas and dust was derived from a supernova, or supernovas — the explosion of an old, massive star. Heavier elements are generated within stars by nuclear fusion of hydrogen, and are otherwise uncommon. We can see similar processes taking place today in so-called diffuse nebulae in this and other galaxies.
Because collisions between large planetesimals release a lot of heat, the Earth and other planets would have been molten at the beginning of their histories. Solidification of the molten material into rock happened as the Earth cooled. The oldest meteorites and lunar rocks are about 4.5 billion years old, but the oldest Earth rocks currently known are 3.8 billion years. Sometime during the first 800 million or so years of its history, the surface of the Earth changed from liquid to solid. Once solid rock formed on the Earth, its geological history began. This most likely happened prior to 3.8 billion years, but hard evidence for this is lacking. Erosion and plate tectonics has probably destroyed all of the solid rocks that were older than 3.8 billion years. The advent of a rock record roughly marks the beginning of the Archean eon.
If you were able to travel back to visit the Earth during the Archean, you would likely not recognize it as the same planet we inhabit today. The atmosphere was very different from what we breathe today; at that time, it was likely a reducing atmosphere of methane, ammonia, and other gases which would be toxic to most life on our planet today. Also during this time, the Earth's crust cooled enough that rocks and continental plates began to form.
It was early in the Archean that life first appeared on Earth. Our oldest fossils date to roughly 3.5 billion years ago, and consist of bacteria microfossils. In fact, all life during the more than one billion years of the Archean was bacterial. The Archean coast was home to mounded colonies of photosynthetic bacteria called stromatolites. Stromatolites have been found as fossils in early Archean rocks of South Africa and western Australia. Stromatolites increased in abundance throughout the Archean, but began to decline during the Proterozoic eon. They are not common today, but they are doing well in Shark Bay, Australia.
The name Proterozoic comes from the Greek "earlier life” since in this eon life form had started. One of the most important events of the Proterozoic was the gathering up of oxygen in the Earth's atmosphere, although oxygen was undoubtedly released by photosynthesis well back in Archean times, it could not build up to any significant degree until chemical sinks.
Throughout the history of the Earth, there have been times when the continental mass came together to form a supercontinent followed by the break-up of the supercontinent and new continents moving apart again. The first supercontinent called Nuna or Columbia was formed about 2.0–1.8 billion years ago. After this supercontinent had broken up another supercontinent called Rodinia was formed 1 billion years ago by accretion and collision of the fragments. After the break-up of Rodinia about 800 million years ago, it is possible the continents joined again around 550 million years ago and this hypothetical supercontinent is sometimes referred to as Pannotia or Vendia. The evidence for it is a phase of continental collision known as the Pan-African orogeny, which joined the continental masses of current-day Africa, South-America, Antarctica and Australia. It is extremely likely, however, that the aggregation of continental masses was not completed, since a continent called Laurentia (roughly equivalent to current-day North America) had already started breaking off around 610 million years ago. It is at least certain that by the end of the Proterozoic eon, most of the continental mass lay united in a position around the south pole.
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