Fossil dating techniques
Fossil dating techniques
It does contain a modicum of truth, however, in that the largest volume of stromatolitic formations was likely formed by biogenic processes involving photosynthetic cyanobacteria.Cyanobacteria’s metabolic byproduct, oxygen, rusted the earth, pumped enormous oxygen poison to them into earth’s atmosphere, and in so doing paved the way for aerobic-based life to emerge and diversify; cyanobacteria’s contributions to life led to their own prodigious decline.
While formation by colonies of cyanobacteria is probably the primary mechanism for formation of surviving stromatolites in the deep time of the Archaean and half way through the Proterozoic, it is unlikely to have been the only mechanism.The figure indicates the paucity of localities where finding the oldest fossils exists. As previously noted, stromatolites are most often described as biogenically-produced structures formed by colonies of photosynthesizing cyanobacteria.However, this is an enormous oversimplification given that the weight of scientific evidence suggests that all three domains of life (the Archaeans, Eubacteria, and Eukaryotes) appeared in the Archaean Era, and thus the so-called microbial mats would have contained representatives among all three domains.So too have many Stromatolites from the Proterozoic.Production of stromatolites has been relatively minor during the Phanerzoic Eon with its entirely different reef ecosystems.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.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.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).Microbial communities diversified through time, with eukaryotic organisms eventually joining the mix.