Hunt for the oldest

signs of life on Earth

Studies from 3.5 billion-year-old pillow lava in South Africa offer new evidence in the hunt for the oldest life on Earth.

Research on the origin of life has taken off during the past few years, and at the forefront of studies on this topic we find research groups at the Department of Geosciences at the University of Bergen . A great deal of international interest was aroused a few years ago when Harald Furnes, together with geologist Ingunn H. Thorseth and marine biologist Terje Torsvik, showed that micro-organisms and bacteria can be found several hundred metres below the seabed, without access to sunlight and fed by chemical substances in volcanic rocks.

International debate

Furnes has used these “biomarkers” to find out just how far back in time we can trace living organisms. Findings from the Barberton Greenstone Belt in South Africa indicate that they go back 3.5 billion years in time. The oldest traces of ancient life forms that are not in dispute today are “only” 2.7 billion years old.

An international debate is under way regarding whether ancient finds of biological material are capable of being confirmed. Australian fossils found in sedimentary rocks in the 80s suggested that life already existed on Earth 3.5 billion years ago. Towards the end of the 90s, geologists believed that they had found microscopic particles of carbon in a 3.87 million-year-old stone from the Isau Belt in Greenland - 700 million years after the formation of the Earth. However, doubt was cast on these sensational findings when other researchers managed to demonstrate identical processes without the help of bacteria, but by changing conditions such as pressure and temperature.

Little affected by geological conditions

The area in which the studies were carried out has not been particularly affected by subsequent geological processes, so that it is relatively unaltered. The researchers studied a number of parameters that provide good indications that their findings are of biological origin. All the studies done in the area point in the same direction: that there was organic life in these rocks 3.5 billion years ago, a short time after the formation of the primal sea. Furnes and his colleagues go back to the early history of the Earth and study the topmost layer of the ancient seabed crust, a 500-1000-metre thick layer of lava pillows. These pillows all display a rim of glass, because their outer layers have cooled so rapidly. The bacteria colonise the glass surfaces, which provide them with nutrients and energy, and etch their way down through the glass, gradually creating a network of microscopic tunnels only a couple of micrometers in diameter. The structure of these tunnels is very similar to others that have been found in pillow lava beds in “modern” ocean crust that is still covered by the sea.

Everything suggests organic material

“Water originally brought the bacteria into tiny natural crevices in the glass, and it was here that they found a means of survival. One of the methods we used to demonstrate that these tunnels were created by bacteria was to study carbon levels in the material, which confirmed that it contained organic material. Comparisons of the isotopic composition of the cracks in the glass rim and in the centre of the pillows produced the same results,” says Furnes.

Glass soon turns into minerals, and the glass rims of the lava pillows have been transformed into chlorite. Samples taken from the Barberton Greenstone Belt show that the chlorite has grown over the tiny tunnels formed by the bacteria, supporting the theory that they settled on the glass not long after the lava had cooled sufficiently to allow them to survive, at about 100 degrees Celsius.

“The rocks have been dated to 3.5 billion BP, so the traces of organic material would seem to be about the same age,” says Furnes, whose work was presented in the journal “Science” in 2004. The article entitled “Gas or life” achieved 14th place in “The Year in Science: Top 100 Stories” in 2004.

www.geo.uib.no

Back to front page

To order a free example of the paper edition of Features, contact the Communication and Media Centre either by e.mail or telephone +47 55 58 69 00