Friday, September 23, 2011

Cradle of Humankind, Gauteng


The Cradle of Humankind Site comprises a strip of a dozen dolomitic limestone caves containing the fossillised remains of ancient forms of animals, plants and most importantly, hominids. The dolomite in which the caves formed, started out as coral reefs growing in a worm shallow sea about 2.3 billion years ago.

The Cradle of Humankind site lies mainly in the Gauteng province with a small extension into the neighboring North West Province, and covers 47 000 hectares of land mostly privately owned. The Cradle of Humankind Site comprises a strip of a dozen dolomitic limestone caves containing the fossillised remains of ancient forms of animals, plants and most importantly, hominids. The dolomite in which the caves formed, started out as coral reefs growing in a worm shallow sea about 2.3 billion years ago.


As the reefs died off they were transformed into limestone which some time later was converted into dolomite. Millions of years later after the sea had receded, slightly acidic groundwater began to dissolve out calcium carbonate from the dolomite to form underground caverns. Over time the water table dropped and the underground caverns were exposed to the air. The percolation of acidic water through the dolomite also dissolved calcium carbonates out of the rock into the caverns, which formed stalactites, stalagmites and other crystalline structures. Continued erosion on the earth's surface and dissolution of the dolomite eventually resulted in shafts or avens forming between the surface of the earth and the caverns below. Bones, stones and plants washed down these shafts into the caves; and animals and hominids fell into the caves, became trapped and died.The bone and plant remains became fossilized and along with various stones and pebbles became cemented in a hard mixture called breccia.


At least seven of the twelve sites have yielded hominid remains. In fact, together these cave sites have produced over 850 hominid fossil remains, so that to date they represent one of the world's richest concentrations of fossil hominid bearing sites.The scientific value of this area lies in the fact that these sites provide us with a window into the past, to a time when our earliest ancestors were evolving and changing. Scientists have long accepted that all humans had their origins in Africa.

Through the use of biochemical evidence they have argued that the split of the human lineage (Hominidae) from that of the African apes took place around 5-6 million years ago. The study of hominid fossils from sites in Africa thus enables scientists to understand how these hominids have changed and diversified since then.

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