Assignment 4 - 1 Earths History a Formation of earth 4.6bya...

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1. Earth’s History a. Formation of earth: 4.6bya b. Origin of Life: 3.5bya c. Late Proterozoic Glacations: 900-540mya d. Beginning of the abundant fossil record…: 540mya e. Extinction of Dinosaurs: 65mya f. Pleistocene Glaciations: 1.8mya g. End of most recent glaciation: 10,000 years The formation of life on earth was a vital factor in creating the atmosphere and climate we live in today. Life on earth originated approximately 3.5 billion years ago. This number has been determined from the discovery of the fossilized remains of tiny, single-celled organisms. The oldest microfossils were collected from the Apex Chert, which is part of the 3.5 billion year old Warrawoona Formation in Australia. These ancient bacteria had a huge effect on the atmosphere which initially had much different composition. The earliest bacteria know as methanogens produced chemical reactions which generated methane (a greenhouse gas). This helped to create an atmosphere abundant in CO 2 , H 2 as well as CH 4 , all gases which create a strong greenhouse effect which would have made up the Sun’s weaker energy flux. At about 2.7bya photosynthetic organisms named cyanobacteria evolved. Cyanobacteria produced oxygen which was released into the atmosphere oxidizing iron, creating Banded iron-formations and other geological markings. The rise in oxygen produced an increase in stratospheric ozone, shielding the earth from harmful solar radiation
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Assignment 4 - 1 Earths History a Formation of earth 4.6bya...

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