When these scientists began studying some of the world’s oldest rocks, they discovered something that changes what we know about life on earth

On the wild summits of Canada’s Torngat Mountains, scientists study some of the oldest rocks on earth. Thousands of miles away, researchers in a Japanese laboratory pick apart the chemical elements that make up this ancient landscape. Now, they’ve discovered evidence of life on earth – almost four billion years in the past.

Since human beings first arrived on planet earth, they have sought to understand it in different ways. Both science and religion have produced many varied theories about the origins of life, each having their time in the spotlight over the years.

Today, most scientists believe that the earth came into being just over 4.5 billion years ago. But what happened next is still the subject of some debate. Although some materials, such as zircon crystals, have been dated to around 4.3 billion years ago, the first signs of life were not thought to have emerged until some 500 million years later than that.

However, recent research could change all that. In a paper published in the journal Nature in September 2017, a team of scientists from the University of Tokyo announced the surprising results of an expedition to Labrador, on the east coast of mainland Canada.

There, the researchers had been studying some of the oldest rocks in the world. From a region known as the Torngat Mountains in Canada’s far northeast, they are thought to be around four billion years old – formed when the earth was still in its infancy.

At the time, our planet would have looked very different to how it does today. With no oxygen in its atmosphere, it presented a very hostile environment to potential life. However, the University of Tokyo researchers discovered something fascinating buried in the ancient rocks.

Apparently, the Torngat Mountains are home to a region known as the Saglek Block – the world’s oldest known stretch of a special type of rock. Known as metasedimentary, it is formed when layers of sediment solidify over the years. Eventually, high temperatures and pressures spark a recrystallization process in the rock.

Within the Saglek Block, the scientists discovered samples of graphite, a type of carbon. Although graphite can be formed in a number of ways, one of these is as a direct result of decaying organic matter. Previously, the oldest graphite known to have formed from living organisms was dated at between 3.7 and 3.8 billion years old.

However, the rocks in the recent study are thought to date back some 3.95 billion years. What’s more, the carbon found within them was shown to contain a particular blend of isotypes. And with its high concentration of carbon-12, it’s likely that this graphite came from an organic source.

So does this prove that there was life on earth 3.95 billion years ago? If true, this discovery will push back the date of the oldest known organic graphite by some 150 million years. In fact, it suggests that living matter was thriving on the earth just 500 million years after it first formed.

Previously, an event known as the Late Heavy Bombardment, during which asteroids rained down on the earth, was thought to have preceded any life on the planet. However, this new evidence suggests that organisms may have developed in tandem with this cataclysmic event.

“Life started on earth during the heavy bombardment of meteorites, which is amazing,” enthused the University of Tokyo’s Yugi Sano, a senior researcher. Interestingly, the discovery lines up with other researchers’ theories about how life on earth might have emerged.

Back in 2016, a team of Australian researchers announced the discovery of 3.7-billion-year-old fossils in Greenland. Thought to be stromatolites, they represent a relatively complex step along the evolutionary chain. According to science writer Ed Yong, this suggests that life in a simpler form must have emerged long before.

Image: Tsuyoshi Komiya/University of Tokyo via CBC.ca

Interestingly, their age wasn’t the only significant thing that scientists observed about the pieces of graphite. Apparently, the study also revealed evidence that the organisms from which it had formed may have been autotrophic, or capable of producing their own food from their environment.

However, not everyone has jumped on the study’s claims that life on earth could be far older than first thought. According to experts, there are other factors that could have caused the ancient graphite to form, such as the arrival of a meteorite or a geochemical reaction.

According to the Swedish Museum of Natural History’s Martin Whitehouse, another problem could lie in the dating of the rock in which the graphite was found. Apparently, the study used the oldest possible date for the region – even though that was taken from rocks some miles away from the graphite source.

“Regardless of the veracity of the biogenic evidence from the graphite,” Whitehouse told the Guardian in September 2017, “the claim that it is the oldest requires that the geochronology is watertight. If it’s younger than about 3.8bn years, it isn’t very exciting anymore.”

Additionally, there is also the possibility that, at some point in history, younger graphite was somehow incorporated into the warping metamorphic rock. However, the team believes that they have ruled out this possibility by studying the temperatures at which the graphite was formed.

By studying the structure of the graphite itself, they were able to determine that it was created at between 997 and 1152 °F. Crucially, this temperature matches that which caused the surrounding metamorphic rocks to form – implying that the graphite was there from the start.

And although there have been some doubts about the research, many scientists are excited about its potential implications. “If they are right, and this is life at 4 [billion] years ago,” enthused geochemist Matthew Dodd from University College London to the Guardian, “it’s saying life can begin and make ends meet in a very hostile environment.”