How does the earth's early atmosphere composition differ from today's composition?
1 Answer
the Earth early atmosphere varied very little from today's composition.
Explanation:
In 1952 the consensus of the scientific community was that the early atmosphere was a reducing atmosphere that had been formed from the condensation of a cloud of interstellar dust and gas. Research since that time has shown that the early atmosphere always had significant amounts of Oxygen similar to the present atmosphere.
The famous Urey Miller experiment that showed that organic molecules could be produced by an electrical discharge in an experimental flask containing, methane , ammonia , hydrogen, water and no Oxygen. This experiment was based on the assumption of an early reducing atmosphere before the evolution of photosynthesis.
The assumption of an early atmosphere without oxygen has been called into serious question due to scientific evidence. Kimroth and Kimberly stated that no evidence of an oxygen free atmosphere is found in any sedimentary rocks ( Canadian Journal or Earth Science 1976 pp 1161- 1185) The Oxygen rich Iron Oxides are found in the earliest sedimentary rocks, formed long before the proposed evolution of photosynthetic cells.
The examination of the earliest living cells found the presence of an enzyme that protects against Oxygen ( Lumsden and Hall Nature 257 1975 p 670-672) There would be no need of the enzyme without atmospheric Oxygen. The new theory is that the early atmosphere was formed by outsourcing from volcanos. This formed an atmosphere with little or no Hydrogen, methane or ammonia. Also the early atmosphere would have had at least 25% of the present percentage of Oxygen from the break down of water into Oxygen and Hydrogen. (RT Binkman Cal Tech) The Hydrogen due to its lighter density would escape into space leaving Oxygen.
The strongest evidence for a reducing atmosphere is that the proposed chemical evolution of life is impossible in the presence of Oxygen. (James Walker Evolution of the Atmosphere 1977 p 262) Life did come into existence, So a circular argument is that since life can not come into existence by chemical evolution in the presence of oxygen and it is believed that life evolved from non life by chemical evolution, it is believed that the early atmosphere had no Oxygen.
The present scientific evidence is that the early atmosphere was very similar to the present atmosphere. This is a change from earlier theories of the composition of the early atmosphere.
