Stromatolites are not only Earth's oldest of fossils, but are intriguing in that they are our singular visual portal (except for phylogenetic determination of conserved nucleic acid sequences and some subtle molecular fossils) into deep time on earth, the emergence of life, and the evolving of the beautiful forms of life of modern time.

A small piece of stromatolites encodes biological activity perhaps spanning thousands of years.

Microbial communities diversified through time, with eukaryotic organisms eventually joining the mix.

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Stromatolites and their close cousins the thrombolites, are rock-like buildups of microbial mats that form in limestone- or dolostone-forming environments.

Together with oncoids (formerly called "algal biscuits" or "Girvanella"), they typically form by the baffling, trapping, and precipitation of particles by communities of microorganisms such as bacteria and algae.

What rock has not been lost may of course be buried deeply.

The figure to the left shows Precambrian exposure within the United States. and Wisconsin and Minnesota particularly have much old rock, and not surprisingly, considerable Stromatolites and banded iron.

New stromatolite localities have continued to be discovered in various places such as the Bahamas, the Indian Ocean and Yellowstone National Park, to name but a few localities.

Stromatolites occur throughout the world, but become diminishingly uncommon in the Archaean.Stromatolite-building communities include the oldest known fossils, dating back some 3.5 billion years when the environments of Earth were too hostile to support life as we know it today.We can presume that the microbial communities consisted of complex consortia of species with diverse metabolic needs, and that competition for resources and differing motility among them created the intricate structures we observe in these ancient fossils.In some cases, they can form inorganically, for example when seawaters are oversaturated with certains chemicals resulting in precipitation.Stromatolites are defined as laminated accretionary structures that have synoptic relief (i.e., they stick up above the seafloor).In broad terms, stromatolites are fossil evidence of the prokaryotic life that remains today, as it has always been, the preponderance of biomass in the biosphere.