Palaeontologists may marvel at dinosaur fossils, but microscopic goo sparks excitement. A discovery in Greenland pushes the origins of life back 3.7 billion years. New research reveals liquid pockets in garnets containing amide structures, suggesting that ecosystems were already thriving at that time. These findings offer fresh insight into early life, showing that Earth hosted diverse life much earlier than previously thought.
Palaeontologists may drool over dinosaur fossils, but what gets geologist Minik Rosing going? Microscopic goo.
In 1999, Rosing discovered the carbon signature of life in a Greenlandic rock formation, pushing the beginnings of life back to at least 3.7 billion years ago.
Now, new analytic techniques tell more of the story. Palaeontologist Magnus Harding and an interdisciplinary team of researchers have identified tiny pockets of liquid in garnets from the same area of Greenland that contain remnants of amide groups – protein structures that have survived intense heat, pressure and truly unthinkable timescales.
The garnet goo “does not tell us about how life originated, but it tells us that even large and well-functioning ecosystems already existed 3.7 billion years ago – perhaps even earlier than that,” Rosing says.
A natural museum
Rosing, now a professor at the University of Copenhagen in Denmark, grew up at a reindeer station, an eight-hour boat ride from Nuuk, Greenland’s capital. That remote country is home to a natural geological museum.
At high elevations in southwestern Greenland, the climate is too inhospitable for plant life, leaving dramatic rock formations exposed. “You have rocks that have been scoured by ice during the retreat since the last ice age,” Rosing says. “This is like walking on a polished marble floor; you can absolutely see all the structures in the rocks.”
The glacier-polished panels are a window into the Isua supracrustal belt, a geological structure so old that geologists are not certain how it formed – it may even predate tectonic plates. “We do not know of anything that is older,” Rosing says.
Microscopic life and a bank-vault gem
Palaeontologists who research “young life” – on the timescale of dinosaurs and early mammals – get the luxury of fossilised skeletons. But looking deeper in time, this kind of physical evidence becomes scarcer and scarcer.
The earliest life on Earth “did not have hard parts” to fossilise, Harding explains. “We do not have bones or teeth.”
Australia’s Pilbara Craton, home to what may be the first evidence of life on land, contains 3.5-billion-year-old stromatolites – rocky concretions made by colonies of microbes, kind of like how the skeleton of a coral reef is formed.
But the Isua supracrustal belt is older still. “These rocks have undergone much higher temperatures and much higher pressures,” Harding says. “All these structures – the microfossils and stromatolites – have been destroyed if they were ever there.”
For any trace of life from the time of the Isua supracrustal belt to survive requires an extraordinary defence against the forces of geology. As such, Harding and his team looked to garnets.
Although garnets are an unassuming and affordable semiprecious stone at your local jeweller, they are a tank geologically, forming under extremely high pressure and temperature. “Garnets are very rigid – it is a mineral that is very structurally sound,” Harding says. “It is very, very difficult to physically destroy garnet. If you lock something away in there, it is a good bet it is going to stay in there and not be altered too much.”
Secrets hidden in garnet stones
The garnets the researchers were interested in are far from gem quality. They are ruddy-brown rocks streaked with layers of graphite, a crystalline form of carbon used as pencil lead. “With the graphite, seeing whether anything else is present is difficult,” Harding says. “We identify the presence of these liquid inclusions by breaking open the garnets.”
When researchers crush tiny samples of the garnet between two glass slides, the pressurised liquid “erupts or splashes out” after being trapped for time immemorial, he says. The most volatile or unstable elements evaporate right away, leaving researchers with a telltale residue on the garnet’s surface. “It is like half-dried paint,” says co-author Tue Hassenkam, a nanoscientist at the University of Copenhagen.
To tease out the goo’s secrets, the researchers turned to atomic force microscopy. “This is a technique in which you generate images by feeling your way across the surface,” Hassenkam explains. A very sharp, fine probe is brushed over an object to trace the contours of its surface. “This cantilever is so sensitive that it can feel small vibrations. So we flash a laser on the surface and can heat up specific wavelengths,” he says. By measuring its vibrations, the researchers can determine what a material is made of – kind of like striking a glass with a pen to determine by its resonance whether it is glass or crystal, Rosing adds.
What they found and how it got there
The atomic force microscopy found the fingerprint pattern of amide groups, a chemical structure that forms the backbone of proteins.
“This is very interesting” that these structures were able to survive “being pressure cooked” from within the safety of a garnet, Hassenkam says. But how did they get inside in the first place?
Harding says the most likely scenario involves aquatic life. As microscopic organisms in a lake or ocean die, they drift through the water column and settle into layers on the lake bed or sea floor. Over time, these layers are buried deeper and deeper until they petrify – “the sediments are made into a rock, basically, but the organics are still there,” he says. Then, at some point, the area must have undergone a regime of extreme pressure and heat that formed garnet crystal seeds, which grew indiscriminately around pockets of dead microorganisms.
The researchers think that the garnet goo represents a rich community. “They are not little traces of one little organism that lived in solitude and did nothing,” Rosing says. “This is actually an ecosystem with many different creatures that was functioning at that time.”
Rocks older than life Itself
To Rosing, this is like a tiny message in a bottle across eons telling us that life was pretty good at the time – not the hellscape that geologists once theorised when they dubbed this period the Hadean, after the Greek underworld.
Liquid water – the most important requirement for life – arrived on the scene 600 million years before, Hassenkam points out. Even on an evolutionary timescale, that is a long time. “For us in present day, 600 million years ago takes us back to the Cambrian explosion, where you go from single-cell organisms to life as we know it. So this means that the microbes in the Isua supracrust belt are most likely very far from the origin of life.”
It is rather poetic that, to date, no part of the geological record indicates rocks older than life. “In all parts of Earth’s history that are observable, life was here,” Rosing adds.
“It is not just that Earth is different from other planets and therefore can hold life,” Rosing says. “It is different because it has life. That is what caused it to be so different.”
