Traces of graphite in ancient Canadian rocks were produced by microorganisms 3.95 billion years ago, according to new research. (Image: Tsuyoshi Komiya, The University of Tokyo)
Researchers working at a sedimentary rock formation in northern Labrador, Canada, say they have uncovered evidence of primordial life in 3.95 billion-year-old rocks. The discovery, which is already drawing scrutiny and some scepticism, suggests that microbial life emerged relatively quickly after the formation of our planet.
The idea that life could have emerged so long ago — and in such an alien environment — is nothing short of astounding. During the Eoarchaean Era, when Earth was just 500 million years old, our planet's landscape was littered with volcanoes, and its newly-formed crust was still too hot to support tectonic activity. Asteroids and comets pounded the surface at an uncompromising pace, delivering the chemical building blocks required for life. Back then, Earth's atmosphere was choked in methane and ammonia, without any free floating oxygen to speak of. Even the Sun looked different, shining down with a brightness around 75 per cent of what we see today.
It was in this hostile environment that early life had to emerge, take root, and survive. New evidence published today in Nature is offering further evidence that primordial Earth, despite these harsh conditions, was able to sustain life. Traces of biological activity locked inside badly-warped 3.95 billion-year-old sedimentary rocks may represent some of the earliest known examples of life on Earth, pushing back the origin of life by about 150 to 250 million years.
Finding evidence of primordial life isn't easy, mostly because ancient rocks have been severely twisted and transformed over time. The oldest fossils date back about 3.77 billion years, but microbial organisms can leave behind other traces of their existence as well.
Prior to this discovery, some of the oldest evidence of life was detected in rocks from Greenland, including 3.7 billion-year-old rocks from the Isua belt and 3.8 billion-year-old rocks from the Akilia rock formation. But the rocks analysed in this latest discovery, made by Tsuyoshi Komiya from the University of Tokyo, comes from the poorly studied Saglek Block in northern Labrador, Canada, which have been dated to about 3.95 billion years old.
A microscopic image of the globular shape produced by the graphite grains. (Image: Tsuyoshi Komiya, The University of Tokyo).
For the study, Komiya looked for biogenic (i.e. biologically produced) graphite grains locked within the rocks. These aren't fossilized imprints of the microbes, but the stuff they left behind. Komiya and his colleagues conducted a detailed geological analysis of the rocks, while also measuring the chemical compositions of the graphite, which appeared to be indicative of biological processes. Importantly, they ruled out the possibility that the rocks were contaminated with younger rocks. The graphite contained within these 3.95 billion year old rocks, argue the researchers, is of biological origin, and thus suggestive of life.
"This is an excellent paper with lots of information and another definite proof that life existed back in the Eoarchean," said Dominic Papineau, a researcher at University College London, in an interview with Gizmodo. "I think the authors make a solid case, although it could have been further compelling by looking at the elemental and molecular compositions of the graphite and the mineral associations with the graphite."
Papineau is concerned that the graphite may have been inorganically produced, and believes the researchers should have done more work to prove its biogenic nature. Matthew Dodd, a PhD student who works with Papineau at UCL, also likes the paper, but he shares the same concern.
"I agree with their conclusions based on this preliminary data. However, the study is somewhat limited in evidence for biogenecity of the graphite," Dodd told Gizmodo. "The authors rely solely on the isotopic composition of carbon in the graphite, therefore it will take further analyses to provide conclusive evidence."
Dodd says that the chemical signature detected by Komiya could have been produced by a variety of chemical processes without the need for biology.
"Isotopically light carbon is found in meteorites, for example, and we know this is inorganic," he said. "Future work will need to establish other lines of chemical evidence such as whether there are biologically critical elements such as nitrogen, sulphur and phosphorus within this graphite, for the biogenecity of the carbon to be properly assessed."
Interestingly, Dodd says these findings could tell us something about how life emerged not just on Earth, but on other planets as well, including Mars.
"It narrows the gap of life's emergence [on Earth] from between 4.3 billion (the age of the oceans — life requires water) to 4 billion years ago," he said. "It provides a cross-roads to life's occurrence elsewhere in the Solar System, since Mars is believed to have been similar to Earth at this point in time. Therefore, we should expect to find life on Mars four billion years ago if life is a straightforward process to kickstart. If we don't find evidence for life on Mars at this time...then Earth is a special case in the solar system — and potentially the Universe."
Indeed, the fact that life got started so quickly on Earth, and under such stressful conditions, should lead us to believe that it's a common occurrence throughout the Universe. But as Dodd points out, the longer we go without finding traces of life elsewhere — Mars included — the more we might start to think our planet has something special going on.