Geochemists have found evidence that life likely existed on Earth at least 4.1 billion years ago, 300 million years earlier than previous research suggested. The discovery indicates that life may have begun shortly after the planet formed 4.54 billion years ago.
The research is published today in the journal Proceedings of the National Academy of Sciences.
“Twenty years ago, this would have been heretical; finding evidence of life 3.8 billion years ago was shocking,” said Mark Harrison, co-author of the research and a professor of geochemistry at UCLA.
“Life on Earth may have started almost instantaneously,” added Harrison, a member of the National Academy of Sciences. “With the right ingredients, life seems to form very quickly.”
The new research suggests that life existed prior to the massive bombardment of the inner solar system that formed the moon’s large craters 3.9 billion years ago.
“If all life on Earth died during this bombardment, which some scientists have argued, then life must have restarted quickly,” said Patrick Boehnke, a co-author of the research and a graduate student in Harrison’s laboratory.
Scientists had long believed the Earth was dry and desolate during that time period. Harrison’s research, including a 2008 study in Nature he co-authored with Craig Manning, a professor of geology and geochemistry at UCLA, and former UCLA graduate student Michelle Hopkins, is proving otherwise.
“The early Earth certainly wasn’t a hellish, dry, boiling planet; we see absolutely no evidence for that,” Harrison said. “The planet was probably much more like it is today than previously thought.”
The researchers, led by Elizabeth Bell, a postdoctoral scholar in Harrison’s laboratory, studied more than 10,000 zircons originally formed from molten rocks, or magmas, from Western Australia. Zircons are heavy, durable minerals related to the synthetic cubic zirconium used for imitation diamonds. They capture and preserve their immediate environment, meaning they can serve as time capsules.
The scientists identified 656 zircons containing dark specks that could be revealing and closely analysed 79 of them with Raman spectroscopy, a technique that shows the molecular and chemical structure of ancient microorganisms in three dimensions.
Bell and Boehnke, who have pioneered chemical and mineralogical tests to determine the condition of ancient zircons, were searching for carbon, the key component for life.
One of the 79 zircons contained graphite, pure carbon, in two locations.
“The first time that the graphite ever got exposed in the last 4.1 billion years is when Beth Ann and Patrick made the measurements this year,” Harrison said.
How confident are they that their zircon represents 4.1 billion-year-old graphite?
“Very confident,” Harrison said. “There is no better case of a primary inclusion in a mineral ever documented, and nobody has offered a plausible alternative explanation for graphite of non-biological origin into a zircon.”
The graphite is older than the zircon containing it, the researchers said. They know the zircon is 4.1 billion years old, based on its ratio of uranium to lead; they don’t know how much older the graphite is.
The research suggests life in the universe could be abundant, Harrison said. On Earth, simple life appears to have formed quickly, but it likely took many millions of years for very simple life to evolve the ability to photosynthesize.
The carbon contained in the zircon has a characteristic signature, a specific ratio of carbon-12 to carbon-13, that indicates the presence of photosynthetic life.
“We need to think differently about the early Earth,” Bell said.
Wendy Mao, an associate professor of geological sciences and photon science at Stanford University, is the other co-author of the research.
The research was funded by the National Science Foundation and a Simons Collaboration on the Origin of Life Postdoctoral Fellowship granted to Bell.
Remains of microorganisms at least 3,770 million years old have been discovered by an international team led by UCL scientists, providing direct evidence of one of the oldest life forms on Earth.
The NSB contains some of the oldest sedimentary rocks known on Earth which likely formed part of an iron-rich deep-sea hydrothermal vent system that provided a habitat for Earth’s first life forms between 3,770 and 4,300 million years ago. “Our discovery supports the idea that life emerged from hot, seafloor vents shortly after planet Earth formed. This speedy appearance of life on Earth fits with other evidence of recently discovered 3,700 million year old sedimentary mounds that were shaped by microorganisms,” explained first author, PhD student Matthew Dodd (UCL Earth Sciences and the London Centre for Nanotechnology).
Published in Nature and funded by UCL, NASA, Carnegie of Canada and the UK Engineering and Physical Sciences Research Council, the study describes the discovery and the detailed analysis of the remains undertaken by the team from UCL, the Geological Survey of Norway, US Geological Survey, The University of Western Australia, the University of Ottawa and the University of Leeds.
Prior to this discovery, the oldest microfossils reported were found in Western Australia and dated at 3,460 million years old but some scientists think they might be non-biological artefacts in the rocks. It was therefore a priority for the UCL-led team to determine whether the remains from Canada had biological origins.
The researchers systematically looked at the ways the tubes and filaments, made of haematite, a form of iron oxide or ‘rust’, could have been made through non-biological methods such as temperature and pressure changes in the rock during burial of the sediments, but found all of the possibilities unlikely.
The haematite structures have the same characteristic branching of iron-oxidising bacteria found near other hydrothermal vents today and were found alongside graphite and minerals like apatite and carbonate which are found in biological matter including bones and teeth and are frequently associated with fossils.
They also found that the mineralised fossils are associated with spheroidal structures that usually contain fossils in younger rocks, suggesting that the haematite most likely formed when bacteria that oxidised iron for energy were fossilised in the rock.
“We found the filaments and tubes inside centimetre-sized structures called concretions or nodules, as well as other tiny spheroidal structures, called rosettes and granules, all of which we think are the products of putrefaction. They are mineralogically identical to those in younger rocks from Norway, the Great Lakes area of North America and Western Australia,” explained study lead, Dr Dominic Papineau (UCL Earth Sciences and the London Centre for Nanotechnology).
“The structures are composed of the minerals expected to form from putrefaction, and have been well documented throughout the geological record, from the beginning until today. The fact we unearthed them from one of the oldest known rock formations, suggests we’ve found direct evidence of one of Earth’s oldest life forms. This discovery helps us piece together the history of our planet and the remarkable life on it, and will help to identify traces of life elsewhere in the universe.”
Matthew Dodd concluded, “These discoveries demonstrate life developed on Earth at a time when Mars and Earth had liquid water at their surfaces, posing exciting questions for extra-terrestrial life. Therefore, we expect to find evidence for past life on Mars 4,000 million years ago, or if not, Earth may have been a special exception.”