Extremophiles

There exists a group of extremophiles called cryptoendoliths. Cryptoendolithic organisms are those that live in the microscopic spaces within rocks, such as pores between aggregate grains. These also include endolithic organisms that inhabit fissures, aquifers, and faults filled with water deep within the surface. The picture is of an endolithic cyanobacteria. This photosynthetic endolith can be seen boring into a piece of crystalline calcite. These cyanobacteria have also been observed boring into limestone, grains of sand, mussel shells, corals, and other substrates consisting of carbonate. Such an organism could have survived the harsh conditions of early earth. The ability to survive in a place where few other organisms can would have played a major role in the survival of these cyanobacteria. Not to mention their ability to grow and thrive in a substrate generally devoid of essential nutrients. The ability to use photosynthesis to generate energy must have also played an important role in the survival of this organism to the present day. Fossil evidence shows that such endolithic cyanobacteria were alive and thriving millions, if not billions, of years ago.