If you were able to travel back to visit the Earth during the Archaean Era, you would likely not recognize it is the same planet we inhabit today. The atmosphere was very different from what we breathe today; at that time, it was likely a reducing atmosphere of methane, ammonia, and other gases which would be toxic to most life on our planet today. Also during this time, the Earth's crust cooled enough that rocks and continental plates began to form.

It was early in the Archaean that life first appeared on Earth. Our oldest fossils date to roughly 3.5 billion years ago, and consist of bacteria microfossils. In fact, all life during the more than one billion years of this Era was bacterial.

There were stromatolites, colonies of photosynthetic bacteria which have been found as fossils in Early Archaean rocks of South Africa and Western Australia. Stromatolites increased in abundance throughout the Archaean, but began to decline during the Proterozoic. They are not common today.