A History Of Deep Time – Part 2

Prof Maarten de Wit (Published by University of KwaZuluNatal)

Ancient life forms

Volcanic basalts associated with the komatiites are also of great interest. These rocks often display spectacular bulbous features known as pillow lavas. The outer rims of the pillows comprise volcanic glass in which microscopic traces of the world’s oldest life forms have recently been discovered in the form of hair-like tubes. These tubular structures are also found today in glassy margins of pillow lavas that cover the modern oceans in great abundance, and are constructed by bacteria that consume chemical ingredients from the rock-glass to sustain their metabolism: these bacteria literally ‘eat’ rock.

The new Mpumalanga finds confirm without doubt that simple life was rife on earth about 3 500 million years ago, and that most of its upper oceanic crust was teeming with bacteria. Other microscopic fossils have also been discovered in the Barberton Mountainland in numerous other rock types, suggesting that there was a significant diversity of bacteria. Thus between 3 200 and 3 500 million years ago primitive life in Mpumalanga was already exploring a number of ecological niches, and had established the world’s oldest biodiversity hot spots.

LEFT: An outcrop of komatiite, a unique volcanic rock type discovered along the Komati River in 1969.

RIGHT: Spinifex textures in polished komatiite.

The young planet

Numerous other important observations of and experiments on the rocks from the Barberton Mountains have provided insight into the hostile environmental conditions that prevailed on earth in those early days. For example, tiny spherules have been found in thin rock layers that are widely spread throughout the central parts of the Barberton Mountains. These are the rock equivalents of hailstones that dropped out of clouds of molten rock droplets spewed into the atmosphere as a result of the extreme heat and mechanical energy liberated during periods of intense meteorite bombardment and volcanic activity at that time.

In addition, detailed structures preserved in the sedimentary rocks of the imposing ridges that dominate the road sections between Barberton and
Josefsdal, and across the Swaziland border into Piggs Peak, illustrate that the earth-moon tidal system was already operational. From these rock ‘inscriptions’ one can calculate also that the moon was considerably closer to earth, that the earth was spinning faster, and that terrestrial days were consequently shorter than they are today.

A particularly intriguing metalliferous rock mass near Bon Accord, close to Malelane, was made up almost entirely of iron and nickel (most of it was
mined out by the middle of the last century), probably representing a chunk of the inner core of the early earth that was embedded in its rocks near the surface at a time of dynamic upheaval. Scientists have also tested rocks from the central parts of the Barberton Mountainland to prove that the earth at that time had a self-generating magnetic field, although this field was probably not as strong as it is today.

These and many other geological treasures provide tiny glimpses into the workings of our young planet. But the record is fragmentary, and there is still much that we do not understand. Scientists have only just scratched the surface of Mpumalanga, and more remains to be discovered. The importance of studying the geological history of the Barberton Mountainland cannot be overemphasised: it has allowed South African scientists over the past 50 years to define the very cutting edge of research into the beginnings of the earth’s history and, in doing so, helped to shape the future of new emerging sciences such as geo-biology and astro-biology, and will continue to play a role in planning future missions to Mars in the quest for signs of life on other planets.

TOP: Ocelli, or ‘eyes’, in pillow lava along the Komati River.

ABOVE: Ocelli with mushroom-like flow structures in pillow lava along the Komati River.

Click here to read Part 1 -A History Of Deep Time

Click here to read Part 3 – A History Of Deep Time