How old is life on Earth? It’s a question that intrigues and infuriates scientists—and geologists think the answer lies inside Earth’s oldest rocks. There, ancient microbes left behind clues to their long-ago existence. And now, reports The Washington Post’s Sarah Kaplan, scientists peering into some of those ancient stones think they’ve found the earliest-ever evidence of life on Earth.
A new study, published in the journal Nature, describes fossilized microorganisms thought to be between 3.77 and 4.28 billion years old. They were found in Quebec, Canada’s Nuvvuagittuq greenstone belt, which is home to some of Earth’s most ancient rocks. Inside, researchers found the fossils of what they say are long-gone bacteria left behind during Earth’s tumultuous early days.
The jasper belt in which the fossils were found is thought to have once been an undersea vent. There, researchers say, the vents played hosts to prehistoric microbes—much like modern vents, where heat-loving bacteria loves to gather. The team thinks that the remnants of some filament-like microbes absorbed iron deposits from the water after they died and slowly turned into stone. Over time, the rocks became part of the bigger belt and the rock emerged from the sea. Now, researchers think they see the remnants of those tiny fossilized structures. They look like tiny tubes.
But the tubes’ size has some scientists skeptical. As geobiologist Frances Westall tells The New York Times’ Carl Zimmer, the filaments are too big to be that old, both compared to other finds in the same rock belt and because bacteria at the time would have had to be super small to sustain low-oxygen conditions on early Earth. Another geobiologist tells Kaplan that the dating process used by the research team is controversial and that the rock could be much younger than the paper contends. Other experts aren’t sure the tubes are the remnants of life at all.
The team begs to differ. The tubes look remarkably similar to remnants left by organisms in much younger rocks. The reserachers say that the existence of carbon-12 isotopes inside graphite also found in the rocks—tell-tale signs of carbon and, hence, life—makes their case even stronger. And if they’re right, the find is staggering indeed.
If life did exist on Earth 4.28 billion years ago, that would be half a billion years earlier than scientists previously thought. Even the youngest estimate for the new microbes' age, 3.77 billion years, is still 70 million years older than the next oldest microbes. The microbes described in the new study are pretty different from the ones now thought to be the world’s oldest. And that, in turn, would mean that Earth was able to sustain relatively diverse kinds of bacteria early on. At the time, Earth was in the midst of a scourge of meteorites as extraterrestrial rocks pounded the new plant's surface. That barrage wasn't exactly hospitable to any would-be Earth inhabitants—so if microbes managed to set up camp there anyway, the discovery could change the way scientists see the period now called the Late Heavy Bombardment.
It’s an intriguing possibility, but one that will be subject to intense scrutiny. And that’s okay—if the fossils have really been around since a few million years after Earth came into being, they can surely withstand a few years of scientific argument and validation.