Pictured here are the fossil remains of the first living organisms known to ever flourish on earth: the stromatolites. They were not giant, ugly mushrooms, as you might expect from this picture. They were in fact, structures built by microbes, and made of sediment they trapped in their secretions.
Stromatolites are formed by colonies of marine bacteria or algae. They build the stromatolites up into mounds, like the one above, by secreting a layer at a time. The algae and bacteria are shallow water critters that absorb their energy from the sun and don’t require oxygen, thus they were able to thrive in the oxygen free atmosphere of early earth. Though they lived more than 2.7 billion years ago, they still exist today, but they aren’t abundant anymore.
This stromatolite fossil was collected in northern Arkansas from the Ordovician Everton Formation, and is about 450 million years old.
For more views of stromatolites, click here