An international team of paleontologists has discovered in Quebec, Canada, the oldest physical evidence of life on Earth — fossils that date back 3.77 billion years. The discovery was reported online today in the journal Nature.
Hematite tubes from the NSB hydrothermal vent deposits that represent the oldest microfossils and evidence for life on Earth. Image credit: Matthew Dodd, University College London.
Microscopic filaments and tubes formed by ancient iron-loving bacteria were found encased in quartz layers in the Nuvvuagittuq Supracrustal Belt (NSB).
The NSB contains some of the oldest sedimentary rocks known on the planet which likely formed part of an iron-rich hydrothermal vent system that provided a habitat for Earth’s first life forms between 3.77 and 4.3 billion years ago.
Before this find, the earliest accepted evidence for life were 3.7-billion-year-old stromatolite fossils from the Isua Greenstone Belt in south-west Greenland.
“Our discovery supports the idea that life emerged from hot, seafloor vents shortly after planet Earth formed,” said Matthew Dodd, a Ph.D. student at the University College London and first author on the study.
“This speedy appearance of life on Earth fits with other evidence of recently discovered 3.7 billion year old sedimentary mounds that were shaped by microorganisms.”
Dodd and co-authors found the filaments and tubes inside centimeter-sized structures called concretions or nodules, as well as other tiny spheroidal structures, called rosettes and granules, all of which they 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,” said study lead author Dr. Dominic Papineau, also from the University College London.
The researchers looked at the ways the tubes and filaments, made of hematite — the mineral form of iron (III) oxide (Fe2O3) — 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 hematite structures have the same characteristic branching of iron-oxidizing 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.
The team also found that the mineralized fossils are associated with spheroidal structures that usually contain fossils in younger rocks, suggesting that the hematite most likely formed when bacteria that oxidized iron for energy were fossilized in the rock.
“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,” Dr. Papineau said.
“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.”
“These discoveries demonstrate life developed on Earth at a time when Mars and Earth had liquid water at their surfaces, posing exciting questions for extraterrestrial life,” Dodd said.
“Therefore, we expect to find evidence for past life on Mars 4 billion years ago, or if not, Earth may have been a special exception.”
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M.S. Dodd et al. Evidence for early life in Earth’s oldest hydrothermal vent precipitates. Nature 543: 60–64; doi: 10.1038/nature21377
