Pre-Cambrian

The Pre-Cambrian by: i.am.ns.10

The [|Pre-Cambrian]is 7/8 of earth’s history, from 4.6 BYA to 543 MYA. Many important events took p lace during this time. 4.6 billion years ago, Earth was forming in an accretion disc. The sun formed, shrinking by gravitational compaction and underwent nuclear fusion. Surrounding particles began to coalesce by gravity into larger lumps, or planitesimals, which turned into planets. Then 800 million years later, the first continents form when lava covering the earth hardened. About 4 billion years ago an ocean covered the world. In this ocean, the first life appeared 3.5 billion years ago. After the Pre-Cambrian era, there was a time period called the Cambrian period. During this time period massive evolution of life began to happen and new ecosystems began to form from new life forms that were very different from the Pre-Cambrian.

Back then, earth looked much different than today. For the first 800 million years, there were no continents. But as time passed and the earth cooled down, the layer of lava covering the earth hardened, forming the first continents.  T hen it rained continuously for thousands of years and much of the earth became covered by an ocean. The dry land was centered at the South Pole, forming the first super continent, [|Rodinia]. North America looked nothing like it does today. It was positioned on its side across the equator with today’s east coast facing south. Our New England would not form for many millions of years. The climate back then was also very different. For a long time the atmosphere was made of methane, ammonia, hydrogen, and carbon monoxide, making earth very dangerous for life forms to thrive until oxygen became present later on. The temperature was hot with constant rain, thunder, and lightning. However at least twice during the Proterozoic eon the earth froze.

G eology was a very important part of the Pre-Cambrian finding these rocks nowadays is difficult because these rocks are buried deep below the surface. However these rocks can still be found in a few places, such as the [|Grenville Mountains]in eastern Canada, were weathering and erosion have worn the mountains down to their innermost core were bare rock is exposed. The rocks are mainly metamorphosed sedimentary rock with igneous intrusions that have been folded and overturned by colliding rocks creating induced comp ression. Fossils are also hard to find because organisms from that time period were mainly soft bodied, which decompose and don’t leave their bones behind. However there are still some examples of fossils and imprint fossils. One example of a fossil is [|stromatolites]. Stromatolites are huge stacked plates of limestone particles from cyanobacteria that clustered together. These are very rare today, and are usually found in Africa and Australia. There are other versions of stromatolites such as collenia fossils, which are cone shaped stromatolites. Another type of fossil that was found are moneran fossils, which are some of the first prokaryotic cells fossilized In some of the oldest rocks present on earth. Also fossilized protists hardened and became different types of rock, like chalk. Fossils of algae are rare due to the fact that they didn’t have a solid composition and rotted away.

Life was a very important part of the Pre-Cambrian because life was just starting and was new on our planet. Although scientists can’t exactly pinpoint when life started, the earliest bacteria findings are about 3.5 billion years old. These bacteria are very similar to today’s bacteria and have only sl ightly changed. The first bacteria to appear were prokaryotic cells; cells without a nucleus. Then 1 billion years ago, the first eukaryotic cells, protists appeared. These cells had a nucleus. These were some of the first cells to photosynthesize to create energy. A product of photosynthesis is oxygen, and therefore oxygen became present in the atmosphere and built up over time. However due to the new increase in oxygen in the atmosphere, 90% of all bacteria died, leaving space for new bacteria to grow, and eventually more complex life forms as well. These first multicellular species were called [|vendian animals] and consisted of soft-bodied creatures such as jellyfish, ediacaria and dickinsonia. Every animal today evolved from these prehistoric creatures.

click here to see my bibliography click here to my reflection