Precambrian Time
Precambrian Time is a long amount of time from the formation of Earth, around 4.6 BYA, that ended about 542 MYA. Precambrian time takes up over 80% of Earth’s history. It can be divided into the Hadean Eon (4.6 BYA- 3.9 BYA), Archean Time (3.9 BYA- 2.5 BYA), and the Proterozoic Eon (2.5 BYA- 542 MYA). Precambrian Time is often referred to as “The Age of Life”. During Precambrian Time the climate varied. In the beginning it was very hot. It was so hot that there could be no oceans because all the water was evaporated. Later, around 4,550 to 3,900 MYA, Earth’s climate cooled. Because of the cooling climate and air it was finally cold enough for the water vapor to collect and fall as precipitation. In Precambrian Time there were a lot of volcanos which formed igneous rock. When sediment from the igneous rock chipped it gathered together with other pieces of rock to form new rock. This new rock helped form cratons, which were the early bases of the continents. During Precambrian Time the continents were extremely different than they are today. During this time there were two different major “Supercontinents”, which are a bunch of the continents pushed together. The first of the Supercontinents appeared 2.5 BYA and lasted until about 2.1 BYA. The second Supercontinent was Rodinia and lasted from 1.8 BYA until somewhere around 1 BYA and 900 MYA. During Rodinia today’s North America was in the middle with all the other continents surrounding it. Even now the continents shift a few centimeters each year. During this this time the landforms went through major changes including new land being formed. 400 MYA, the oceans were just forming. They formed when rain fell to Earth collected on Earth’s surface. At this time oceans covered most of Earth’s surface. 4 BYA Earth’s first sedimentary rock formed. Before that point there was only igneous rocks because there were so many volcanoes. The earliest organisms appeared 3.4 BYA. These organisms were all bacterias. At first the bacteria used chemical fuel for energy. Then, 2.5 BYA the bacteria started to use photosynthesis. Photosynthesis helped turn bacteria into some of the first simple plants. Finally, only 600 MYA the first multi-celled organisms appeared. All of the multi-celled organisms were soft-bodied. These first life forms helped create oxygen. Precambrian Time ended about 542 MYA. During the Proterozoic Eon there was a mass extinction that wiped out many of the life forms. It happened around the emergence of complex/multicellular life forms. |
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