Study finds Earth's soils hosted life early on
Way before trees or lichens evolved, soils on Earth were alive, as revealed by a close examination of microfossils in the desert of northwestern Australia, reports a team of University of Oregon researchers.
|Abandoned pit at Mount Goldsworthy near Mount Grant in Western Australia |
[Credit: Phillip Schubert, Creative Commons]
Other mineral and chemical tracers found in the rocks also required weathering in soils of the distant geological past, he said.
"Life was not only present but thriving in soils of the early Earth about two thirds of the way back to its formation from the solar nebula," Retallack said. The origin of the solar system -- and Earth -- occurred some 4.6 billion years ago.
The study outlines a microbiome of at least five different kinds of microfossils recognized from their size, shape and isotopic compositions. The largest and most distinctive microfossils are spindle-shaped hollow structures of mold-like actinobacteria, still a mainly terrestrial group of decomposers that are responsible for the characteristic earthy smell of garden soil.
Other sphere-shaped fossils are similar to purple sulfur bacteria, which photosynthesize organic compounds in the absence of oxygen while leaving abundant sulfate minerals in the soil.
|Graphic shows types of tiny fossils found at Mount Grant in Western Australia |
[Credit: Mick Lissone/public domain]
Retallack referred to the memoir "Lab Girl" published this year by Hope Jahren, a geobiologist at the University of Hawaii, who wrote: "For several billion years, the whole of the Earth's land surface was completely barren. Even after life had richly populated the oceans, there is no clear evidence for any life on land."
"The newly recognized microfossils may have supplied some evidence at last," Retallack said.
The ancient soils with sulfate salts and microfossils come from the Pilbara region of Western Australia. They are superficially similar to those found recently by the Mars rover Curiosity. "They may," he said, "be useful as guides for the discovery of life on other planets."
Author: Jim Barlow | Source: University of Oregon [November 17, 2016]