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3.5 billion years ago, life not only found its way, but also diversified, so many years later you can still observe differences in what’s left.
The Earth has undergone many cycles of geological uplift and destruction, so little remains of the rocks from when life first began. Parts of Western Australia are one of the few exceptions, with traces of microbial life dating back 3.48 billion years.
Barite is stable under high temperature and high pressure conditions and is difficult to dissolve in water, making it a particularly promising material for this research.
The samples of black-layered barite analyzed by Lena Weimann, a PhD student at the University of Göttingen, and colleagues were taken from calderas, cavities that form after volcanic eruptions and are often filled with lakes. The hot fluids within the caldera provide both energy and nutrients for today’s life forms, and such environments are strong candidates for where life first evolved. The research team discovered carbonaceous particles trapped within barite. Its molecular size suggests it was left behind by early life forms.
“As our findings show, original traces of the first organisms can still be found in very old materials,” Wyman said in a statement.
Three types of organic molecules were found in barite (barium sulphate) from the Pilbara Craton in Western Australia, two of which were apparently present at the same time.
Image credit: Gerhard Hundertmark
Not much information remains about these creatures, but we do know that they must have been unicellular. That may suggest that there is little we can learn. But when Wyman’s team combined several high-resolution observing techniques, they discovered three different types of carbonaceous material he called clusters.
These show that even at this early point, life forms at the time were evolving to fill separate niches.
The most common populations are found at the edges of single growth zones of barite crystals. The second is found finely distributed within the barite matrix, and the third is found in quartz veins that cross the barite. The first two were likely deposited as barite crystallized, but quartz appears to have entered the system at least 200 million years later with a third population.
The researchers believe that Population 1 arises from organic particles that accumulate on crystal surfaces where water and sediment meet. As hydrothermal flow decreased or temperatures dropped, rocks could become populated with biofilms or microbial mats, such as those formed by today’s single-celled organisms.
As the flow accelerated, it carried along with it particles that may have come from organisms living elsewhere. At this point, the crystallinity was high and the particles were dispersed within the growing crystal, creating population 2.
The research is published open access in the journal Precambrian Research.
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