This is easily the oldest fossil we’ve ever featured. This small, dark rock is a stromatolite, a sedimentary rock consisting of layer upon layer of oxygen-producing microorganisms. These single-celled microbes were so simple they lacked a DNA packaging nucleus, but were responsible for possibly the most drastic changes the earth has undergone. By producing oxygen as a waste product, they were the only major source of atmospheric oxygen at the time, and therefore critical for the development of more complex life.
• Some stromatolites date back an astounding 3.4 billion years, making them the oldest record of life on planet Earth.
• When these microbes lived, Earth’s atmosphere had no oxygen, the oceans were euxinic—void of oxygen and rich in hydrogen sulfide (H2S).
• These microbes oxygenated Earth and made it habitable for life as we know it.
• Add this artifact to your fossil collection.
Stromatolites are layered sedimentary formations that are created by photosynthetic cyanobacteria. These microorganisms produce adhesive compounds that cement sand and other rocky materials to form mineral “microbial mats”. In turn, these mats build up layer by layer, growing gradually over time. A stromatolite may grow to a meter or more. Although they are rare today, fossilized stromatolites provide records of ancient life on Earth.
Stromatolites are layered biochemical accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains in biofilms (specifically microbial mats), especially cyanobacteria. They exhibit a variety of forms and structures, or morphologies, including conical, stratiform, branching, domal, and columnar types. Stromatolites occur widely in the fossil record of the Precambrian, but are rare today. Very few ancient stromatolites contain fossilized microbes.
While features of some stromatolites are suggestive of biological activity, others possess features that are more consistent with abiotic (non-biological) precipitation. Finding reliable ways to distinguish between biologically formed and abiotic stromatolites is an active area of research in geology.
Most stromatolites are spongiostromate in texture, having no recognisable microstructure or cellular remains. A minority are porostromate, having recognisable microstructure; these are mostly unknown from the Precambrian but persist throughout the Palaeozoic and Mesozoic. Since the Eocene, porostromate stromatolites are known only from freshwater settings.