The evolution of the atmosphere: the story and the evidence
Issue 347 | Page 59 | Published Dec 2012
The Earth's primary atmosphere, which was similar to that of the gas giant planets, was soon lost, and a secondary atmosphere was established by outgassing from the early Earth and from colliding debris. The composition of this atmosphere was probably similar to present-day volcanic emissions but with a tiny percentage of photochemically produced oxygen. In this atmosphere, early anaerobic bacterial life evolved, including photosynthesising cyanobacteria that produced oxygen.
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