(CN) — Diverse microbial life existed on Earth at least 3.75 billion years ago, and maybe as many as 4.28 billion years ago, according to a new study from researchers at University College London that challenges the conventional view of when life began.
The study, published Wednesday in the journal Science Advances, suggests that a variety of microbial life may have existed on primordial Earth, possibly as little as 300 million years after the planet formed.
“I have been working on these rock samples for the past 14 years and these new findings are the culmination of that work,” Dominic Papineau, associate professor in geochemistry and astrobiology at UCL and lead author of the study, said in an email to Courthouse News.
“With a lot of perseverance, and using many different scientific approaches and techniques, we were able to discover the oldest fossils on Earth,” Papineau continued.
For the study, Papineau and his team analyzed a rock the size of a fist from the Nuvvuagittuq Supracrustal Belt in Quebec, Canada, that they estimate to be between 3.75 and 4.28 billion years old.
The team had previously found tiny filaments, knobs and tubes in the rock that appeared to have been made by bacteria. Not all scientists, however, agreed that the structures, which date about 300 million years earlier than what is commonly accepted as the first sign of ancient life, were of biological origin.
Now, after extensive further analysis of the rock, the team discovered a much larger and more complex structure – a stem with parallel branches on one side that is nearly a centimeter long – as well as hundreds of distorted spheres, or ellipsoids, alongside the tubes and filaments.
“We have discovered, in 2017, what we believe are the oldest microfossils on Earth, that could be as old as 4.28 billion years of age,” Papieau said in a short video about the discovery.
He said the structures he and his team found are akin to modern microorganisms living in deep sea hydrothermal vents in the Pacific, Arctic and Indian oceans.
“For more than 40 years, microbiologists have told us that the origin of life most likely occurred in hydrothermal vent environments, with microorganisms eating iron and probably sulfur, as we can infer from our own observations,” Papineau said in the film clip.
Papineau said the discovery of the rock and microorganisms within it also marks an advancement of scientific exploration of life in space. Some of the same instruments he and his team have used to collect data on microfossils are used on the Mars Perseverance Rover that is investigating biological signatures on the Red Planet.
“We have not found direct evidence of extraterrestrial life that has compelled the scientific community to adopt the view that there absolutely is life,” Papineau explained in the video, “but I think we’re inching closer by doing these discoveries and by pushing the clock back, because it not only tells us what to look for, but also how to look for it, and it also tells us that we need a bit of volcanism, liquid water, some of the right chemicals, which are common, and a very short amount of time for life to emerge and evolve on a planetary surface.”
Papineau and his team say that while some of the structures they found could possibly have been created through chance chemical reactions, the “tree-like” stem with parallel branches was most likely biological in origin, as no structure created only through chemistry has been found like that.
The researchers also provided evidence of how the bacteria got their energy in different ways. They found mineralized chemical byproducts in the rock that are consistent with ancient microbes living off iron, sulfur and possibly also carbon dioxide and light through a form of photosynthesis not involving oxygen.
Having once been a chunk of seafloor, Quebec’s Nuvvuagittuq Supracrustal Belt, where the sample was found in 2008, contains some of the oldest known sedimentary rocks on Earth, thought to have been laid down near a system of hydrothermal vents, where cracks on the seafloor let through iron-rich waters heated by magma.
The research team sliced the rock into sections about as thick as paper in order to closely observe the tiny fossil-like structures, which are made of hematite, a form of iron oxide or rust, and encased in quartz.
They compared the structures and compositions to more recent fossils as well as to iron-oxidising bacteria located near hydrothermal vent systems today. They found modern-day equivalents to the twisting filaments, parallel branching structures and distorted spheres, in modern day oceanic locales, for instance close to the Loihi undersea volcano near Hawaii, as well as other vent systems in the Arctic and Indian oceans.
In addition to analyzing the rock specimens under various optical and Raman microscopes, the researchers digitally recreated sections of the rock using a supercomputer that processed thousands of images from two high resolution imaging techniques.
In their analysis, the team concluded that the hematite structures could not have been created through the squeezing and heating of the rock over billions of years, pointing out that the structures appeared to be better preserved in finer quartz that isn’t affected by heat and pressure as much as coarser quartz.
The researchers also looked at the levels of rare earth elements in the fossil-laden rock, finding that they had the same levels as other ancient rock specimens, which confirmed that the seafloor deposits were as old as the surrounding volcanic rocks.
Prior to this discovery, the oldest known fossils were found in Western Australia and dated to 3.46 billion years ago, though some scientists have also doubted their status as fossils and have argued they are not biological in origin.
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