The Barberton Makhonjwa Mountains in Mpumalanga, which were officially added to the World Heritage Site List earlier this year, are one of the world’s oldest geological structures, with volcanic and sedimentary rock dating back 3.6 to 3.25 billion years – around the time when the first continents were starting to form on the primitive Earth. These mountains were one of the first landmasses to rise out of the ocean and showcase some of the Earth’s oldest surface rocks. The mountains are also believed to contain the oldest signs of life‚ with a micro fossil of bacteria discovered there that is estimated to be 3.1 billion years old.
The rocks found on the Makhonjwa Mountains may not be the oldest rocks on Earth (those occur in Greenland and Canada), but they are the oldest, most well-preserved rocks representing Earth in early Archean times. The Archean Eon is the period when life first formed on Earth. Beginning about 4 billion years ago with the formation of the Earth’s crust, the Archean era marks the formation of Earth’s primitive atmosphere and the emergence of the oceans.
In addition to providing signs of early life on our planet, the Makhonjwa rocks also provide detailed clues about the hostile nature of the palaeo-environments under which life struggled to persist. For example, coping with more potent solar radiation, to which life is particularly sensitive, in a time when Earth's magnetic field was too weak to shield the planet efficiently from the relentless solar wind at the time.
Over the last decade, three types of early Archean biogenic fossils have been found in the area, with all three having living equivalents in our modern world. Trace fossils of single-cell chemo-synthesisers were discovered in igneous rocks from glassy margins of lavas formed at the bottom of Archean oceans. These were dated around 3.47 billion years old. Similar signs of chemophilic bacteria that metabolise on, and devour, such igneous rock far removed from sunlight are abundant in the modern deep oceans.
Fossil microbes were also found in hydrothermal deposits, such as those in and around modern geysers, for example, those found in Yellowstone National Park. Most recently, a new fossil discovery has been made in sedimentary rocks dated around 3.2 billion years old, with the fossils being as old as their host rock.
According to the researchers who made this find, it is likely that these microbes used sunlight for energy. However, a well-known US-based early-life expert suggests they may be single-cell organisms which had their nucleus encased in a membrane, also known as eukaryotes. If this interpretation is correct, then the early split between bacteria and eukaryote might be found within the 300 million year gap that exists between the igneous/hydrothermal bacteria and the new finds out of the Makhonjwa Mountains, which would be a ‘cradle of life’ breakthrough.
But even before the first signs of visible life were discovered by scientists, settlers in the region discovered another treasure: gold. Brothers Henry and Fred Barber, along with their cousin, Graham, discovered payable gold deposits in the Makhonjwa Mountains in 1884, leading to the formation of the town that came to be known as Barberton and one of South Africa’s first gold rushes. Legend has it that the amount of gold found in Golden Quarry, part of the Sheba Mine near Barberton, was so large that miners had to extract rock from gold instead of the other way around.
The town was also the site of the discovery of Gerbera jamesonii, commonly known as the Barberton Daisy. It was the first species of Gerbera to be the subject of a scientific description, studied by J.D. Hooker in Curtis's Botanical Magazine in 1889.
In light of this vibrant history, it comes as no surprise that the area has been declared a World Heritage Site. With the addition of the Barberton Makhonjwa Mountains to the list, South Africa now has 10 World Heritage Sites‚ the most in Africa.