The oldest known signs of life on Earth have been found in northern Quebec, buried in a sheet of potentially 4.3 billion-year-old bedrock that once formed the bottom of the planet's first ocean.
An international team of scientists found fossilized traces of bacteria in iron ore samples taken from the Nuvvuagittuq Greenstone Belt, a rare surviving chunk of the planet's early crust now situated at the northern tip of Quebec. The discovery pushes the scientific timeline for life on Earth back by 100-600 million years, to an era when the no longer molten-hot planet was covered by shallow oceans and dotted by volcanic islands.
Study co-author Jonathan O'Neil, of the University of Ottawa, says the fossilized remains are the "oldest record of life on Earth," and could offer clues about the emergence of life on our planet and others.
The fossilized remains were found near what's thought to have once been a hydrothermal vent, where swirling heat, chemicals and minerals may have given rise to the first single-celled organisms.
"We're not talking about these complex forms of life on the early Earth, but this is where we think it actually happened," O'Neil told CTVNews.ca by phone on Wednesday. He added that the discovery may make it easier to find life on other planets, because it demonstrates that ancient sea floors are prime spots for finding the early signs of life.
"The ingredients are all there," he said. "This is the kind of place you would want to look for when you're trying to find the traces of life."
O'Neil and his colleagues estimate the fossils are approximately 4.3 billion years old, based on techniques used to measure the age of ancient space rocks. He says this more unorthodox technique was necessary for measuring the rock's age, because rocks from the Earth's infancy do not contain the mineral zircon, which is typically used to determine age.
"If we want to come to the parent of these rocks… the very primordial crust, zircons are not useful," he said. "It was the first time that we've used that (measurement) on Earth, simply because no rocks were old enough before that."
He added that bands of zircon mixed into the sample, which would have likely formed later from melted bedrock, were determined to be at least 3.8 billion years old.
The study was published Wednesday in the journal Nature.
The Earth formed nearly 4.6 billion years ago as a molten ball of rock and gas, around the same time as the birth of the sun. Sometime in those early years it's believed another large chunk of space rock slammed into the planet and rebounded into orbit, where it eventually became the moon. The Earth started cooling down after that impact, with the magma-covered surface hardening into the planet's first crust.
The Earth's surface has changed dramatically over its nearly 4.6 billion-year history, and few traces of the original surface remain.
O'Neil says the oldest known rocks in the world are now at the Nuvvuagittuq Greenstone Belt in Quebec. Only one object is thought to be older, and that's a 4.4 billion-year-old grain of zircon found in Australia.
In terms of the search for life on other planets, O'Neil says it might be hard to analyze a rock sample from the recently-discovered planets orbiting TRAPPIST-1, 39 light-years away. However, he says it should help narrow down the search for life on Mars to regions where water once covered the planet's surface.
"Instead of searching the whole planet of Mars, you can target these specific areas," he said, adding that Earth and Mars were "probably very similar" 4.3 billion years ago.
"I wouldn't be surprised to have these type of environments preserved on Mars as well," he said. "This is where life started on Earth… so let's look for them on Mars."
