PHANEROZOIC MICROBIALITES: PROTEROZOIC BAGGAGE OR A NEW BEGINNING?

The greatest changes in the approximate 3.5 billion-year history of microbialites occurred from the Cryogenian (Neoproterozoic) through the Early Ordovician. The significant changes included a decrease in diversity of forms, abundance apparently diminished, branching columnar stromatolites became less prevalent, Conophyton disappeared, constituent grain size increased, dendrolites appeared, and thrombolites and oncoids became more abundant. During this interval of time, profound changes also took place on the Earth. From the microbialite perspective, the most spectacular changes were the expansion of benthic algal eukaryotes, multiple snowball Earth events, the Acraman impact event, the early diversification of metazoans, and widespread biomineralization. The responses of microbial mats to the changes associated with snowball Earth events (extreme climate change, sea level change, ocean and atmosphere change) and the geologically abrupt nature of these changes cannot be underestimated.

The microbialite ecosystem was subjected to a series of potentially catastrophic of events during the Neoproterozoic. The resilience of populations and communities forming microbialites to short-term change (ecological time scale) is well known. Obviously, this is true at evolutionary time scales as well. Multicomponent systems like microbial mats can adjust to change far more effectively than a single component system like a species. Although Phanerozoic microbialites have a microbial legacy (baggage) from the Proterozoic, it was a very different world for microbial mats during the Phanerozoic, in particular at the sub-millimeter scale. The microbialite is the epitome of a survivor.