All life on Earth probably arose from one spark in the early history of the Earth. Some time later, it diversified and branched out into genera that helped it survive.
Exactly when these moments took place has been a point of contention in the scientific community, but new research suggests that both steps may have taken place earlier than we previously thought.
The study, led by University College London researchers, is based on evidence of diverse microbial life inside a fist-sized piece of rock from Quebec, Canada, dated to about 3.75 billion to 4.28 billion years.
In 2017, researchers who discovered it speculated that structures in the rock – tiny filaments, buds and tubes – had been left behind by ancient bacteria.
But not everyone was convinced that these structures – which would push the date of the first signs of life on Earth back by at least 300 million years – were of biological origin.
But after further extensive analysis of the rock, the team discovered an even larger and more complex structure than those previously identified. Inside the rock, there was a stem-like structure with parallel branches on one side that are nearly an inch long, as well as hundreds of distorted spheres or ellipsoids along the tubes and filaments.
“This means that life could have started as little as 300 million years after the Earth was formed. In geological terms, this is fast – about a spin of the Sun around the galaxy,” says lead author of the study, geochemist Dominic Papineau of UCL.
The key question for Papineau and his colleagues was whether it was possible for these structures to be formed through chemical reactions that were not related to living things.
According to the paper, some of the smaller structures could be thought to be a product of abiotic reactions, but the newly identified ‘tree-like’ strain is most likely of biological origin, as no structure like that created through chemical reactions alone has been found before.
In addition to the structures, researchers identified mineralized chemicals in the rock that could have been byproducts of various types of metabolic processes.
The chemicals are consistent with energy recovery processes in the bacteria that would have involved iron and sulfur; depending on the interpretation of chemical signatures, there may even be hints of a version of photosynthesis.
This finding points to the possibility that the early Earth – only 300 million years after its formation – was inhabited by a variety of microbial life.
The stone was analyzed through a combination of optical observations through Raman microscopes (which use light scattering to determine chemical structures) and digital reconstruction of sections of the rock with a supercomputer that processed thousands of images from two high-resolution imaging techniques.
The piece in question was collected by Papineau in 2008 from Quebec’s Nuvvuagittuq Supracrustal Belt (NSB), which was once part of the seabed. NSB contains some of the oldest sedimentary rocks known on Earth. The fossil-filled rock was also analyzed for levels of rare earth elements, with scientists finding that it actually had the same levels as other ancient rock samples, confirming that it was as old as the surrounding volcanic rocks.
Prior to this discovery, the earliest fossil evidence of life was found in Western Australia, which dates back 3.46 billion years. However, a similar claim exists as to whether these fossils were of biological origin.
Perhaps the most intriguing implications of this discovery are what it means for the potential distribution of life in the universe. If life were able to evolve and evolve under the harsh conditions of the very early Earth, then it may be more common throughout the cosmos than we think.
“This discovery implies that only a few hundred million years are needed for life to evolve to an organized level on an originally habitable planet,” the authors tell the paper.
“We therefore conclude that such microbial ecosystems may exist on other planetary surfaces, where liquid water interacts with volcanic rocks, and that these oldest microfossils and dubiofossils reported here from NSB suggest that extraterrestrial life may be more widespread than previously thought.”
The study was published in the journal The progress of science.