Why would early Earth have been toxic for modern day animals? Why were cyanobacteria able to survive

The surface of early earth was mostly molten and volcanic. The atmosphere was hot and highly toxic.

Explanation: Photosynthetic organisms were present when earth was primarily anoxic. photosynthetic organisms were present when earth was primarily anoxic. the early forms of photosynthesis did not produce oxygen as a waste product. cyanobacteria carry out anoxic photosynthesis. the early forms of photosynthesis did produce oxygen, but it was not enough to make a difference in the atmosphere. the early forms of photosynthesis were carried out in the water, and there was no way for the oxygen to move into the atmosphere.

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