Stromatolites
As long as 3 billion years ago, prokaryotes such as cyanobacteria thrived in the warm and shallow oceans and started to build colonial structures where the microorganisms grew together in large mats. Calcium carbonate produced by these microorganisms and sea sediments covered the mats in layers forming laminated, mound-like structures, called Stromatolites. As these Stromatolite mats fossilized, the layers became bands in the rock, preserved as indicators of early life on Earth. |