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Historic study extends chart of life by nearly 1.5 billion years
The Proterozoic Eon, spanning from 2,500 million to 539 million ... Organisms such as ancient marine eukaryotes were often akin to squishy sea sponges, leaving minimal traces in the rock record.
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Major events in the evolution of amino acid synthesis
The subsequent Archean eon (approximately 3,500 million years ago) is known as the age of bacteria and archaea. The Proterozoic eon was the gathering up of oxygen in Earth's atmosphere ...