Scientists claim to have found the oldest evidence of life on Earth – contained in Canadian rocks 3.95 billion years ago, when our planet had no oxygen and was being pelted by asteroids.
A paper published on Thursday in Nature describes grains of graphite found encased in a rock structure called the Saglek Block along the Torngat Mountains in Labrador, northeast Canada. The paper's authors inspected the amount of carbon-12 and carbon-13 in the graphite sample to work out whether or not there were any remnants of microbes.
Looking for carbon-12 versus carbon-13 can be very revealing. Carbon-12 is pretty good – better than carbon-13, anyway – at forming molecules essential to life, such as proteins and carbohydrates. When living organisms die, their carbon-12 atoms can be preserved in rocks. If there's a lot of carbon-12 compared to carbon-13, it's likely there was something alive there.
The team found that the ratio of carbon-12 to carbon-13 in the graphite grains were higher than normal, suggesting that life existed when the rock was some 3.95 billion years ago.
To make sure that the graphite sample really is 3.95 billion years old and not a mixture of old and new graphite, the scientists calculated the temperature range at which the carbon formed.
Graphite granules that look more organised and crystalline are forged at higher temperatures. The scientists calculated that the sample found in the Saglek Block were created between 536oC (996.9oF) to 622 oC (1151.6oF) - a similar range at which the surrounding metamorphic rocks were made too, which hints that the graphite already existed when the rocks were created too.
Earth is estimated to be around 4.5 billion years old. The previous record for ancient life on Earth was also found in Canada in iron and silica rich rocks in Quebec, estimated to contain the remains of bacteria that roamed some 3.77 billion years ago.
Tsuyoshi Komiya, co-author of the paper and a researcher at the University of Tokyo, Japan, said the next step to determining if the graphite is biogenic will involve analysing “other isotopes such as nitrogen, sulphur and iron of the organic matter and accompanied minerals to identify the kinds of organisms," said Komiya of the next step.
"In addition, we can estimate the environment" in which the organisms lived by analysing the chemical composition of the rock itself.
Finding signs of life so early on when the planet was in extreme conditions when it was less than a billion years old might also “provide insight into early life not only on Earth but also on other planets,” the paper concluded. ®