Not only do mats matter now but they mattered even more in the Precambrian. Evidence from stromatolite formations which are fossilized microbial mats, dates their occurrence well back to almost 3.5 Ga bp in the geological record, or about 1 Ga after Earth was formed. During the Proterozoic period, much of the organic “matter” on Earth was tied up in microbial mats. From a global perspective, microbial mats really mattered then. they are thought to have been extensive in coastal and terrestrial aquatic areas and were arguably the major source of primary production on the planet along with phytoplankton.