Kate Ravilious
Scientists working in Canada believe they have discovered some of Earth’s earliest lifeforms – tiny tube like microbes that lived in and around mineral-rich underwater vents. Their claim is contentious, but if proven correct these fossils could push back the origins of life on Earth to as early as 4.28 billion years ago – hundreds of millions of years earlier than currently accepted, and not long after the planet’s formation.
Until recently Western Australia’s Pilbara region held the crown for earliest life, with its 3.48 billion-year-old fossilised shallow-sea microbial colonies, known as ‘stromatolites’. Then last summer the honours transferred to Greenland, with the discovery of stromatolite traces dating to 3.7 billion years. Now the Canadian region of Quebec has topped them both, with signs of deeper ocean microbial life dated to at least 3.77 billion years, and possibly as old as 4.28 billion years – only 250 million years after Earth’s formation.
The microscopic (one tenth of the width of human hair) tubes, knobs and filaments were found in a chunk of ancient ocean floor, known as the Nuvvuagittuq Supracrustal Belt. This particular chunk of ocean floor was riddled with hydrothermal vents, bringing up hot, mineral-rich waters from below.
“The outcrop is very localised within the rock belt and mirrors modern day hydrothermal vent systems, where the chimneys occur in small localised groups,” explains lead researcher Dominic Papineau from University College London.
By analysing the rocks under a microscope Papineau and his colleagues were able to show that the structures, which are made of haematite (a form of iron oxide, or ‘rust’), had the same kind of twisting and branching structure as iron-oxidising bacteria found near hydrothermal vents today.
Using Raman spectroscopy they were then able to identify the minerals associated with the structures, which included graphite, apatite and carbonate; all minerals that are found in biological matter and frequently associated with fossils. Furthermore, the structures were encased in centimetre-sized nodules, which the researchers believe to be the products of putrefaction. The discovery is described in the journal Nature.
The team also compared their finds with 480 million-year-old microbial structures formed around a hydrothermal vent in present day Norway, 186 million-year-old structures from vents in the US Midwest, and present day organisms living around hydrothermal vents. In all cases the similarities were striking.
Amongst the scientific community the finding has caused quite a stir, with some doubting that the rocks are as old as claimed, and others unconvinced that the twisting structures had to have had a biological origin.
But Papineau, who was not expecting to find life in these rocks and was stunned when he found filament structures, counters, “Taken alone none of the features we find are proof that this was living material, but together the nine lines of evidence we have make a compelling case.”
And the finds also reinforce the idea that life on Earth may well have started in the warm mineral soup, associated with hydrothermal vents.
If Papineau and his colleagues have got it right, then it suggests that life may not be as rare as we think.
“Volcanism, water and a bit of carbon appear to be the main ingredients needed for life, and we find that in many places in the solar system, including some of the moons of Jupiter. If life arose so quickly on Earth it increases the probability that life is widespread and abundant and has originated in many places in the solar system,” Papineau told Cosmos magazine.
