3200-2800Ma

Mesoarchean Era

It is believed that early in this period of Earth's history, it was completely covered by ocean. It was only through volcanic eruptions that continents were formed. Seventy percent of the continental landmasses date from this period.

Fossil evidence tells us that around 3000 Ma (3 billion years ago) single celled organisms had evolved, some solitary and some that formed colonies such as cyanobacteria (blue-green algae). It would form large mats, called stromatolites.

Most importantly, it was 3 billion years ago that DNA stopped evolving. It had evolved to use 20 amino acids to make proteins, then stopped. The limit is due to the number of tRNAs we have, one for each amino acid. It is said that we could have evolved to use up to 63 amino acids, which is done by alternate means by the body, and synthetically by science. But when it comes to encoding proteins using transfer RNA, 20 has been the limit for 3 billion years.

Sources

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