Mysterious lenticular organisms lived over 3 billion years ago

Kromberg Formation Microfossils (Image courtesy Dorothy Oehler)
Kromberg Formation Microfossils (Image courtesy Dorothy Oehler)

An article published in the journal “Precambrian Research” describes the comparative study of lenticular microfossils dating back to 3.4 billion years ago. Dorothy Z. Oehler and Maud M. Walsh started working on these microfossils and together with other researchers concluded that the ones found in the Kaapvaal Craton, South Africa, are related to those found in the Pilbara Craton, Australia. Probably they were autotrophic organisms that for some phases of their life cycle lived like plankton.

Kaapvaal Craton and Pilbara Craton are the two last pristine areas from the first supercontinent on Earth, called Vaalbara. We’re talking about an era between 2.7 and 3.6 billion years ago, a time so ancient that the two cratons’ drifting led them to thousands of kilometers away, where today they’re part of two different continents. However, when they were united life forms already existed that could spread from one craton to another and that’s what the authors of this research think.

Maud M. Walsh of Louisiana State University discovered lenticular microorganisms in the Krapberg Formation of the Kaapvaal Craton and sent some samples to Dorothy Z. Oehler of the Planetary Science Institute in Tucson, Arizona, for an analysis. For the first time, they were compared with other microfossils discovered in the Pilbara Craton and that showed many similarities.

Lenticular microorganisms discovered both in the Kaapvaal Craton and in the Pilbara Craton are among the oldest microorganisms with a certain complexity discovered so far since the former were dated around 3.4 billion years ago and the latter between 3.4 and 3.0 billion years ago. The researchers conducted a series of isotopic analyzes and compared their morphology and the types of rocks and geological environments where the fossils were found.

The fossils were found in a type of sedimentary rock called chert in what in ancient times were shallow waters. They already show some complexity, greater than that of other organisms of that time known. Even their size, with their length of a few dozen microns, is greater than that of all other fossils of the time.

Probably those were autotrophic organisms, meaning of the type capable of feeding off inorganic substances and of converting them into the organic ones they need for their sustenance. According to the researchers, they lived part of their life cycle like modern plankton, floating passively in the seas they lived in.

Like so many other ancient fossils, the ones object of this research don’t look like any other known organism. The traces found in the Pilbara Craton indicate that they have existed for at least 400 million years so they had a remarkable success but at a certain point disappeared.

Despite the modern technologies that allow examinations unthinkable only a few years ago that provide extraordinary details of microfossils, the lenticular organisms that are the subject of this research remain in many ways mysterious. Perhaps 3 billion years ago they represented the peak of the evolution of life on Earth but then disappeared. No matter how successful it may be, for any life form a change can arrive that completely wipes it out.

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