HISTORY OF EVOLUTION ON EARTH AND ORIGIN OF SPECIES There are many ways that the history of evolution on earth can be reconstructed. Much of it includes fossil evidence and carbon dating to indicate when things were present on earth. In addition, modern genetics can be used to estimate when a split occurred between different species. Earlier dates, however, remain mainly speculative as there is little genetic or fossil evidence as to when certain things occurred. What remains is a geological timescale of when things were likely to have occurred on earth as part of the history of evolution and origin of species. •
3.8 Billion years ago—this is the best guess available for the beginning of life on earth. It is believed that life first began with RNA species rather than DNA species. There was a common ancestor that gave rise to two main groups in life: bacteria and archaea as the first major split in living organisms.
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3.5 Billion years ago—this is when the oldest fossil records of single-celled organisms first derive from. Shortly after that (about 3.46 billion years ago) the first methanogens (methanogenic archaea organisms) began feeding on methane in the absence of oxygen at this time.
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3 Billion years ago—this is the first record of viruses, although some scientists believe they were first on earth from the time life first began.
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2.4 Billion years ago—this is when the waste product of photosynthetic cyanobacteria, oxygen, began to build up in what’s called the “great oxidation event”. This has been challenged with the idea that other bacteria were responsible for this oxidation event. There was a decline in methane-producing bacteria so that oxygen was allowed to build up about this time.
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2.3 Billion years ago—earth freezes over completely and later melts, leading to more oxygen being released into the atmosphere, further oxygenating the earth.
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2.15 Billion years ago—there is fossil evidence of photosynthesis from cyanobacteria, believed to be the first photosynthetic organisms. Some believe that this in fact happened earlier than this, during the great oxidation event.
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