Fossilized stromatolitesa. all date from 2.7 billion years ago.b. formed around deep-sea vents.c. resemble structures formed by bacterial communities that are found today in some warm, shallow, salty bays.d. provide evidence that plants moved onto land in the company of fungi around 500 million years ago.e. contain the first undisputed fossils of eukaryotes and date from 2.1 billion years ago.

Stromatolites are laminated organo-sedimented calcareous structures formed by bacterias and other microorganisms, that are agglutinated due to diverse minerals such as calcium carbonate. They grow attached to a substrate and emerge vertically from it. Because of their rocky structure, stromatolites have the potential to persist as a fossil. Most fossilized cells were found in these rocks at the seashore. Fossil registers show that similar structured have been inhabiting earth since about 3.500 and 3.800 millions of years, and they have maintained their evolutive line to the actuality. In the present, they can grow in many places in the world, and they can also be found in certain places with extreme conditions.

Stromatolites are the most ancient evidence of life on earth, being the first atmosphere oxygenators.