Tiny tubes thought to have been etched into South African rocks by microbes are at least 3.3 billion years old, scientists can confirm.
A new analysis of the material filling the structures shows they were created not long after the volcanic rock itself was spewed on to the seafloor.
The tubules could therefore represent the earliest “trace” evidence of activity by life on Earth.
The dating work is reported in Earth and Planetary Science Letters.
It is a follow-up study to the University of Bergen team’s discovery of the microscopic tunnels and pits first published in 2004.
The structures are seen in rocks from the famous Barberton Greenstone Belt in the Mpumalanga Province of South Africa.
These rocks were originally erupted underwater but over the course of Earth history have been lifted on to dry land.
The basalt that forms the rock had previously been dated to 3.47-3.45 billion years old, but there was some doubt about when the tubules themselves were created.
By comparing the ratio of different types, or isotopes, of uranium and lead atoms in the material that now fills these tunnels, the team can show they must have been etched by about 3.34 billion years ago – in other words, very soon after the host rock itself was formed. …