Precambrian Time
¨The Precambrian Era covers 7/8th of Earth’s history although paleontologists have found very few fossils of Precambrian organisms. The Precambrian Era was marked by the formation of Earth 4.6 billion years ago, and ended with the explosion of hard-shelled organisms 600 million years ago. It is divided into the earlier Archaean period, when no life existed, and the later Proterozoic Period, in which life did exist. The state of the Earth was much different back then; and was probably ripe enough for life to spring out of non-living particles. First, the Earth formed. The outer covering of the earth cooled and hardened into a crust. The hot molten insides of the Earth leaked out at weak places in the crust. These volcanoes created more rock surface on the young Earth. The clouds formed by the volcanoes caused huge amounts of rain to fall and the oceans were created. Most life forms during this era were in the form of prokaryotic single-celled organisms, but fossil finds started to increase at the end of the period as complex, soft-bodied invertebrates began to develop. Life never spread out to land during this time, because oxygen and ozone levels in the atmosphere were not abundant yet, but life did thrive in the seas at the very least. Stromatolites are among the most famous “organisms” during the Precambrian era, and are formed from the growth of cyanobacteria, which are bacteria with chlorophyll and were instrumental in developing the Earth’s first supply of oxygen. We do not know of any major extinctions during the Precambrian Era due to a lack of fossils, but we do know that the era ended with the explosion of invertebrate life in the seas.
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