Precambiran Extinction Essay, Research Paper
Mass Extinction in the Precambrian
As the decades pass, technological advances have enabled researchers, entrepenures and pondering minds the ability to discover more and more about every aspect of our very existence. Over the past three decades the evolutionary tree of life has been expanded at least seven times over. Major advances have been made in the area of evolution to open the eyes of many to the extensive history of the earth. For the very first time, we have tangible knowledge that life evolved and grew to become a flourishing success during the young ages of the Earth. By 3.5 million years ago life was already well advanced. Before this breakthrough no one could have thought that life occurred so amazingly early, that Earth was inhabited by a huge array of tiny life forms through t the first four-fifths of it?s existence, and no one deduced that evolution itself evolved over geologic time.
All of geological time, the total history of the earth, is divided into major eras and eons. The Precambrian eon marks the approximate age of the earth and spans a time of 4.6 billion years ago to 523 million years ago. This era is known to include approximately 90% of geologic time and covers 4 billion years of Earth history. The time period is not extremely well known or completely understood because rocks from this era are poorly exposed, many rocks have been eroded or metamorphosed, most are buried deep beneath younger rocks and fossils from this time period and are seldom found. There are three eras included in the Precambrian eon, which include the Hadean, Archean and Proterozoic.
The Hadean era ranges from 4.6 billion years ago to 3.8 billion years ago. Included in this period was a time of major changes in the Earth?s formation. It involves the origin of the atmosphere, volcanic outgassing, and H2O, H2, HCL, CO, CO2, N2, and sulfur gases. Little or no free oxygen was present in this period. The evidence that supports the oxygen theory include: Urbanite and pyrite are readily oxidized today, in modern times, but are found unoxidized in sediments from here, chemical ?building blocks? could not have formed in the presence of oxygen and the simplest living organisms have an anaerobic metabolism and would have been killed by oxygen. It also included the origin of the continental crust. Most of the early crust was mafic and the continental developed secondary to that.
The Archean era lasted from 3.8 to 2.5 billion years ago. Upon research and findings, Stomatolites (blue-green algae) have been found in carbonate sediment, algal filament fossils were found aged at 3.5 billion years at the North Pole and in western Australia, and spherical bacterial structures were also found in the area of, present day, South Africa. Rocks found from this era are the products of the early differentiation of small protocontinents, which eventually collided with one another forming larger continents.
The Proterozoic was known to range from 2.5 to .57 billion years ago. In this era, there were major changes in the Earth?s crust as full sized continents assembled and plate tectonics begun to operate.
At least one great extinction took place during the Precambrian. Evidence is now supportive of possible three extinctions causing explosive changes in this time. These extinctions may have been the predetermining factor in encouraging the diversification of life forms. These also set the stage for the Cambrian explosion (543 to 510 million years ago) following the Vendian (523-543 million years ago).