Stromatolite found in Bolivia, South America

It is assumed that stromatolites were formed in areas with low oxygen by microbes. These microbes likely respirated using sulfur. We can make assumptions of other life forms on distant planets also use a sulfur system to live. This stromatolite was formed in the Precambrian period roughly 540 million years ago.

Stromatolite in a triangular shape with swirling circles insideclose up of swirling circles