Walking the geological timeline, beginning with the oldest rocks on earth

In the beginning, the Earth was “formless, void and darkness was over the surface of the deep” (Gen 1 v 2). According to scientists, this is quite an accurate description. About 4 600 million years ago the Earth formed and this phase of the planet is called the Hadeon Eon. The embryonic Earth was a hot place during which time the inner and outer core, mantle and crusts took shape.


The Archaean Eon followed the Hadeon Eon and this is where Mountainlands and the Barberton area fits into the picture due to the Barberton Greenstone Belt – a geological formation that is world famous for its staggering 3 600 million years of earth’s natural history and evolution. And about 3 300 million years ago the first opportunity presented itself for living organisms to evolve and the evidence can be found in rock formations of Mountainlands. There is no other place on Earth where scientists can go to recover as much information about this important formative period of Earth’s history. These highly accessible Archaean exposures present a continuous 350 million year sequence of rocks, from 3600 million years in age. Their physical and chemical characteristics provide an unparalleled repository of scientific information about the early Earth. The outstanding value of these rocks lies in the large number of sites and features that, when combined, provide a unique and as yet only partially explored scientific resource.

The Barberton Greenstone Belt is built up of three major rock sequence formations: The Onverwacht Group, followed by Fig Tree and Moodies Group all belonging to the Swaziland Supergroup. The Onverwacht Group is at about 3470 million years the oldest in South Africa. It consists of, among others, banded iron formations and some of the hottest lava ever to have flowed on the face of the planet. These rocks are so-called “spinifex textured” lavas that are rare in the world but typical of the Barberton Mountain Land. The textures are caused by needle-like crystals of olivine and pyroxene and are named after a needle-like Australian grass. The lavas are called komatiites, after the Komati River near Tjakastad where they have first been identified in the 1960s. Some examples are exposed in Mountainlands Nature Reserve.


The Fig Tree Group (ca. 3250 million years) consists mainly of shales and chert. The Moodies Group dated to about 3230 million years old consists mainly of quartzites and sandstone. Being quartz, these rocks are more resistant to erosion and therefore form prominent topographic highs, such as Saddleback Hill. The Onverwacht rocks contain less resistant minerals and often define the valleys.

Mountainlands Nature Reserve is in the center of this important Archaean geological formation. It is therefore not surprising that the area is recognized in the world of earth science as a unique living laboratory, as the sequences in the Barberton Greenstone Belt record the picture of the birth of the early oceans, the first atmosphere, the first life to appear on the planet and evidence of the formation of the first continent. The Barberton Greenstone Belt is also the only place on Earth where the ancient ocean floor can be studied revealing a unique 7-kilometre record of sedimentary rocks showing evidence of the sea and ancient beaches, inter tidal zones, estuaries and rivers and sand dunes in Mountainlands.

It also shows four layers of impact-produced debris from ancient giant meteorites that struck the Earth. Each of the meteorite impacts evident in this region was larger than the meteorite that struck earth 65 million years ago killing the dinosaurs and it is estimated that one of the impactors was approximately 30 km in diameter. One of the layers of impact produced debris can be found in a rock formation in a secluded valley on Mountainlands.

The origin of life

The discovery of some of the oldest forms of life yet found, going back at least 3, 200 million years – in the ancient rock masses of the Barberton Mountain Lands is also being viewed in scientific circles as one of the most significant finds yet made. The sub-microscopic, unicellular biological structures approach what must have been the very fundamental nucleus from which all animal and plant life evolved. The Barberton Greenstone Belt has revealed that life most likely started as single cell bacteria (Archaeospheroides barbertonsis).

Ultra-thin sections of black cherts (extremely fine-grained silica laid down as a chemical deposit under water) from the Onverwacht Group have revealed small spheres. These are interpreted to be bacterial structures. The Zwartkoppie Formation, the uppermost unit of the Onverwacht Group has been dated at about 3300 million years. This would indicate that the fossils from the Zwartkoppie Formation might quite feasibly be older than 3300 million years – the oldest to be found on Earth

The presence of ancient hot springs in the Fig Tree Group is another convincing line of evidence documenting possible presence of early living organisms. Hot springs offer the ideal environment for the development of living organisms and bacteria. Due to the timeframe of evolution that is revealed in these rocks, this source of early life is home to 85% of the missing fossil record.

LEFT: The petrified evidence of an ancient hot spring from the Mountainlands Nature Reserve found together with others in the Onverwacht formation on the Dycedale area of the reserve. CENTRE: A modern-day hot spring in the Yellowstone Park (USA) indicating the process of formation. RIGHT: Photographed under a microscope, a colonial cyanobacterium as discovered in the region. These primitive cells do not have a true nucleus. The colour is due to chlorophyll, indicating their ability to photosynthesise i.e. produce food using the sun’s rays. Photograph Dr H. Klaasen, courtesy of the Botany Department of the University of Pretoria.

The atmosphere existing when the basic cells flourished was radically different to that known today. Virtually devoid of oxygen, there was a predominance of carbon dioxide with ammonia and other gasses toxic to human life, demonstrating that life can evolve in adverse atmospheres. As these structures evolved they brought about changes in the atmosphere allowing higher forms of life to evolve.

The primitive atmosphere had many similarities to those space scientists say may exist on some of the planets. Because of this, the National Aeronautics and Space Administration (NASA) are interested in information gathered about this period of Earth’s evolution and has funded various research expeditions to the Mountainlands area. Space probes to Mars and Venus have demonstrated that their atmospheres have a large component of carbon dioxide.

Clearly, more research into the dating of the Barberton rocks and in finding additional unequivocal evidence supporting the presence of biological organisms is an exciting avenue of investigation and a key motivating factor for preserving the area.  An ongoing project in this regard is the detailed mapping of the geology of, among others, Mountainlands which has never been undertaken on such a fine scale before.

To learn more about the area’s geology and one of South Africa’s next Wold heritage Sites download the World Heritage Site Tentative listing submission here… or visit the UNESCO website at :