In a new study, a team of scientists announced it has discovered the world’s oldest fossils, dating back some 3.77 billion years (and possibly as far back as 4.28 billion years). The remarkable find, detailed yesterday in the journal Nature, is comprised of a series of microscopic filaments and tubes that researchers believe were formed by bacteria that thrived on iron. If proven true, the fossils would be the oldest direct link to life on Earth—but not everyone is on board with the stunning discovery.

The team of international researchers, led by Dominic Papineau and Matthew Dodd from University College London, discovered the specimens (embedded in quartz) in the remote Nuvvuagittuq Supracrustal Belt, or NSB, along the eastern shore of the Hudson Bay, near Quebec, Canada. The NSB has long been known to researchers as the home of some of the oldest sedimentary rocks in the world, including some dating back to just 100 million years after Earth was formed, some 4.65 billion years ago.

The region was also once part of an iron-rich, deep sea hydrothermal vent system, the researchers said in a statement, providing a fertile ground in which the bacteria thrived. According to Dodd, “our discovery supports the idea that life emerged from hot, seafloor vents shortly after planet Earth formed.” The tiny, wavy, microfossils, made of hematite (a form of iron oxide) and half the width of a human hair, are similar to other iron-oxidizing bacteria that have been found near hydrothermal vents in California and Norway, although those examples have been found to be much younger (450 million years and 180 million years old), according to Live Science.

The oldest fossils found prior to this may have dated back some 3.5 billion years and were discovered in western Australia in 2013. Another contender for the crown may be fossils found in Greenland last summer. Researchers there dated their find to 3.7 billion years ago, but there has been fierce debate since then about the accuracy of the results, in part due to the difficulty in accurately dating when the rocks the fossils were found in were formed.

As with the Greenland find, the NSB study has been challenged by scientists, some of which cast doubt over whether the fossils were really fossils at all. As geologist Martin J. Van Kranendonk told the New York Times, the filaments found in Canada may be “dubiofossils,” with no biological origins. As NBC News reported, it’s also possible that the tubes could have been formed over time, as the sedimentary rocks compressed and shifted along with the Earth’s tectonic plates. Other scientists have pointed to their size, much larger than any previously dated fossils yet discovered, as an indicator that the filaments must be much younger, as it’s believed that early conditions on Earth did not provide enough oxygen to support rapid growth of bacteria.

The team from the NSB study, however, believes it has ruled out any possible non-biological origins for the fossils. Utilizing election microscopes, ion beams and laser imaging, they examined the mineral makeup of the fossils, which showed traces of biological matter and gasses, the aftereffect of putrefying organic material. That finding does have its supporters, among them David Wacey, a researcher at the University of Western Australia who told the New York Times that for him the evidence is a “pretty convincing biological scenario.”

While the debate continues, the NSB team is already looking ahead towards what insight might be gleaned from their discovery, both here on Earth and in space. If the filaments do indeed date back to 3.7 billion years (or even far earlier), that would indicate that some forms of life emerged on Earth much earlier than previously thought—and under much more primitive conditions. As Matthew Dowd noted, “The process to kick-start life may not need a significant length of time or special chemistry, but could actually be a relatively simple process to get started.” And that, he said, means conditions on other planets like Mars, may have been able to support living organisms as well.