Stromatolite specimens

Fossilised stromatolite specimens from Bolivia

Stromatolites are a type of layered sedimentary formation formed mostly of layers of photosynthetic organisms like cyanobacteria.

These layers build up over a very long time, creating the formations we typically refer to as 'stromatolites'.

Stromatolites provide the oldest evidence of fossil lifeforms that we currently have, with some in Greenland dated to between 3695 and 3710 million years old. Others dated to 3480 and 3450 million years old are found in various locations around the world.

Cyanobacteria in particular are thought to have largely been responsible for the increase of oxygen in Earths atmosphere, an event called 'the Great Oxygenation Event' - so really, stromatolites are the main reason you're alive today.