A team of South African and international scientists working in the Barberton area, Mpumalanga, has found evidence of microbial life as old as 3,5-billion years in volcanic glass.
The scene for this find was set in the early 1990s when two of the team members, Norwegian scientist Harald Furnes and Hubert Staudigel, an American, analysed volcanic glass on ocean floors and found micro-tunnels that had been etched out by bacteria in search of nutrients.
Later, in Cyprus, they found these etched tunnels again, this time in uplifted ocean rock 85-million years old and again in Norwegian ocean rocks 400-million years old.
This excited their interest in searching for signs of life in even older rocks, so they contacted Maarten de Wit of the University of Cape Town and made plans to explore the Barberton mountain range, an area in which De Wit has been working for 25 years.
”Barberton sits in a natural mega-donga,” says De Wit.
”It’s like a giant window into the earth.”
Starting about 100-million years ago, there was geological uplift in the Barberton region. As the rivers flowed in new directions, they gouged out deep channels in the rock, eroded the escarpment and exposed a belt of ancient rock, the Barberton greenstone belt.
When thick lava surfaces in the ocean it forms pillows. The outer rim cools very quickly into volcanic glass and the inner lava cools more slowly to form basalt.
These pillow structures are still visible in the Barberton greenstone belt, a mixture of deep sea and surface lava — and it is here, in the rims of the pillow lava, that the research team found tiny preserved micro-tunnels.
These tunnels were filled with fine titanite crystals. After they had formed, minute chlorite crystals grew across them. From similar ancient rocks elsewhere, De Wit and his team know that those chlorite crystals were likely to have grown about 3,48-billion years ago leading the team to believe that the micro-tunnels are at least 3,48-billion years old.
Bacteria have a particular carbon isotope signature, a particular ratio of carbon 12 to carbon 13. The research team has no doubt that the carbon in the tunnels is biological. In the Barberton greenstone belt they believe they have found conclusive proof of microbial life nearly 3,5-billion years old.
Scientists vary in what they accept as evidence of early life, but widely accepted research dates stromatolites — which are mats of cyanobacteria, or the oldest known life — to be at least three billion years old.
The most significant aspect of this research, according to De Wit, is that it has broadened the search for early life.
The team’s paper is published in Science Magazine this week