AUTHOR INTERVIEW: Magaliesberg is where life itself peeked out from the ocean
‘Cradle of Life — The story of the Magaliesberg and the Cradle of Humankind’ is a fascinating and scientific account of our origins
Most people know about the hominid fossils found at the Cradle of Humankind, especially “Little Foot” and the more recent discovery, Homo Naledi. But the 40km swathe that takes in the Cradle and the Magaliesberg is remarkable for several reasons. Not only is it a World Heritage Site and a Unesco biosphere reserve, but scientists the world over agree it was where the first land surfaced on earth, and where early bacterial life accelerated the evolutionary process.
A man who for the past 40 years has plotted the life story of the Magaliesberg and the area around it, is environmentalist Vincent Carruthers, who recently published Cradle of Life — The Story of the Magaliesberg and the Cradle of Humankind. It follows on from his seminal book, Magaliesberg, published in 1990 and revised several times.
“The biosphere region is most extraordinary. It has evidence of the evolution of all forms of life,” says Carruthers, who lives in Johannesburg but has a small bolt-hole in the Magaliesberg, which he bought in 1979. “Most attention has been paid to the fossils of human ancestors, but you can see the signs of the development of all life in the landscape.”
He is talking about the layers of dolomite and limestone, the caves and varied vegetation which palaeontologists, archaeologists, geologists and historians for a century have been studying for clues about our origins.
“Their work had produced a huge body of knowledge about this region, but it is often confined within their particular disciplines,” he says.
“In the book, I try to draw down on all the theories of knowledge and blur the differences between the sciences to give a continuous timeline of events.”
Beginning his timeline 13,800-million years ago — time and matter begin from a singularity in the ‘Big Bang’ — Carruthers was faced with a challenge, and admits the book is “long in timespan and broad in scope”. It is eminently accessible, though, with hundreds of photographs, maps and diagrams.
When I interview him at his Morningside home, he dives straight into the history of our planet, going back into deep time as if it were yesterday, and making links with the present.
“Three-billion years ago, much of the area we today call the Magaliesberg Biosphere was under water. About 3,100-million years ago, the Kaapvaal Craton surfaced, the first piece of stable land mass to appear above sea level. That piece of land suffered a traumatic life: meteors crashed into it, volcanoes erupted around it, it was dumped in the sea, but it revived.”
As the Cradle area subsided under water, one particular group of bacteria called cyanobacteria evolved the ability to photosynthesise, thereafter shaping the way life developed on earth.
“Photosynthesis is one of the most important principles that govern the development of evolution.”
It deposited as a by-product calcium carbonate, or limestone, and released oxygen for the first time.
“This changed everything.”
Tons of limestone, the basis of dolomite rock, were formed in layers like the skin of an onion. These ancient fossils of once prolific bacterial life can be seen in abundance all over the Cradle of Humankind.
“When you see these spheres of thinly layered rocks called stromatolites in that area, know you are looking at something that was alive 2-billion years ago and changed the whole pattern of life.”
“Dolomite is slightly soluble in water. Huge caves developed and as the water seeped in, dissolving the rock and forming caverns.
“The other by-product of photosynthesis was oxygen and this oxidised the free iron to form iron oxide. Billions of years later this was used by the people of the Iron Age to make tools and weapons and later still, it [led to] mines in Pretoria and became the basis for the development of Iscor and the SA steel industry,” says Carruthers, whose book was launched at the Maropeng visitors’ centre on August 24 with a morning of talks by himself and other academics.
Climate change is nothing new, he says:
“It has happened before. When Gondwana [the supercontinent] broke up, and the continents drifted apart, the central parts of the southern African highveld rose, and the ocean currents on the east and west changed. Those changes turned the highveld into a summer-rainfall area with long dry winters. This had a profound effect on evolution.
“Most areas were forested, and when the lifting happened, the long dry winters were not suitable for woodland. So we have the emergence of grass, which can tolerate drought and frost. Trees can’t! The grassland pushed the woodland back, and encroached on and formed savannah — open areas of grass among occasional copses or trees.
“Many forms began to adapt to a savannah habitat. For example, the antelope developed long legs and a ruminant digestive system which could extract nourishment from grass, which a normal animal stomach cannot.” Some of the primates also became less dependent on the forest environment and adapted an upright posture, a large brain and articulate hands to help them survive in savannah. They gradually became human.
The marvellous thing about the Cradle-Magaliesberg region is, when you cross from south to north, you can see the transition from grassland to savannah in the space of a few kilometres.Vincent Carruthers
“The marvellous thing about the Cradle-Magaliesberg region is, when you cross from south to north, you can see the transition from grassland to savannah in the space of a few kilometres. The way in which the climate influenced the ecology and the ecology influenced us is there before your eyes,” he says.
“The great coincidence of the Cradle is that, just at the time that our ancestors were adapting to a more terrestrial life, the surface of the highveld was eroding away to expose the caves in the dolomite below. Searching for food, a few of our ancestors fell into the many caves that had developed.
“A cave is a chemical laboratory; the minerals in the water transformed bones into fossils, and the mixture of sand, stones and lime encased the fossils in concrete. They were stored safely there for people like [Wits professor in palaeoanthropology] Lee Berger to find.”
“They [our ancestors] fell in and died there; they couldn’t get out. As hypothesised by Ron Clarke [an honorary professor research fellow at Wits, who discovered ‘Little Foot’], hominids found the cracks in the rocks conducive to looking for fruit and plants. They fell in and broke their limbs, dying there because they could not get out.
“There are bones of other animals there too — the fossil beds are rich in other fauna. These play out in the story of evolution that is told at the Cradle of Humankind in clear detail: for example, giraffes were originally short-necked. They developed a long neck to enable them to reach up to browse.”
“Climate change and changes in vegetation influenced our development to humans and the exposure of the caves in the Cradle all happened all at the same time, leaving us a rich fossil history of our evolution. After that, from the process of stone tools to iron tools, firearms, wars, and to making nuclear bombs at Pelindaba — in the Cradle, the whole spectrum of history is laid out for science to look at.”