Abundant Early Life
In the June 8 edition of the journal Nature, Australian Centre for Astrobiology doctoral student Abigail Allwood reveals her discovery of a ten kilometer section of an ancient microbial reef system. She says the stromatolite shape associations and other evidence demonstrates no purely physical or chemical processes alone could have produced the entire ecosystem.
The ancient reef is cut off one end by a fault, and at the other as it disappears into what would have been deep water, not liked by the microbial communities that created the stromatolite structures, just like modern ones.
“If you start at the deep water end and trace it along the reef system, the numbers of stromatolite shapes increase and become more complex and varied, just as occurs in biological reef systems throughout the geologic record,” she says. “It is a classical biological response to the environment.”
Her other lines of evidence include the individual structures and the association of morphologies (shapes), the spatial distributions, and the way those relate to the palaeo-environment. Analysis of the rare earth element chemistry (with Balz Kamber, Laurentian University) confirms the deposition of the fine-grained sedimentary rocks known as chert and carbonate that make up the stromatolites happened in a marine environment.
“If you take a vertical section through time there is a brief change from the high temperature hydrothermal and volcanic deposition that dominated the Pilbara at the time to a shallow marine environment in which life flourishes virtually immediately, “ she remarks. “And then back again to another volcanic and hydrothermal episode, when the stromatolites disappear. This speaks volumes about the conditions that may have nurtured early life”
The Pilbara region of Western Australia contains ancient stromatolite structures up to almost 3.5 billion years old and is a key research area for the Australian Centre for Astrobiology. The stromatolites were first described almost three decades ago, and have been a source of spirited debate. Some think they were formed by primitive microbes, whereas others believe they were formed chemically near hydrothermal vents.