Scientists have unearthed what is believed to be the oldest fossils ever discovered, uncovering the remains of microorganisms dated back at least 3.7 billion years.

An international team led by University College of London scientists have provided direct evidence of one of the oldest life forms on Earth after tiny filaments and tubes formed by bacteria that lived on iron were found encased in quartz layers in the Nuvvuagittuq Supracrustral Belt (NSB) in Quebec, Canada.

The NSB is home to some of the oldest sedimentary rocks on Earth, which were likely formed as part of an iron-rich deep-sea hydrothermal vent system that provided a habitat for Earth’s first life forms between 3.7 and 4.3 billion years ago.

“Our discovery supports the idea that life emerged from hot, seafloor vents shortly after planet Earth formed,” Matthew Dodd, the first author and Ph.D. student at UCL’s Earth Sciences and the London Centre for Nanotechnology, said in a statement. “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.”

Prior to the NSB discovery, the oldest microfossils reported were found in Western Australia and were believed to be 3.5 billion years old. However, some scientists thought there might be non-biological artifacts in the rocks.

The international researchers looked at the ways the tubes and filaments—a form of iron oxide or rust called haematite—could have been made through non-biological methods, including temperature and pressure changes in the rock during burial of the sediments. However, the scientists systematically deemed all these possibilities as unlikely.

The haematite structures have the same characteristic branching of ion-oxidizing bacteria found near other hydrothermal vents today and were found alongside graphite and minerals, including apatite and carbonate which are found in biological matter like bones and teeth and are frequently associated with fossils

The scientists also discovered that the mineralized fossils are associated with spheroidal structures that usually contain fossils in younger rocks, which suggests that the haematite most likely formed when bacteria that oxidized iron for energy were fossilized in the rock.

“We 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 we think are the products of putrefaction,” study lead Dominic Papineau, Ph.D., of UCL’s Earth Sciences and the London Centre for Nanotechnology, said in a statement. “They are mineralogically identical to those in younger rocks from Norway, the Great Lakes area of North America and Western Australia.

“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,” he added.

Papineau explained that the discovery could lead to further breakthroughs.

“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,” Papineau said. “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.”

Dodd also used the discovery to theorize about life on another planet.

“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,” Dodd said. “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.”