Vredefort Dome - the world's biggest meteor crater
Two billion years ago a meteorite 10 kilometres wide hit the earth near what is today the town of Vredefort in the Free State, 100km south of Johannesburg. The impact created a massive crater that can still be seen from space - the Vredefort Dome.
The meteorite was a piece of rock bigger than Table Mountain. When it hit the earth, it exploded with a thousand-megaton blast of energy equivalent to bomb fired by a trillion tons of dynamite. The impact was so powerful it immediately turned 70 cubic kilometres of solid rock into dust. The turmoil it caused to the planet's climate may have increased oxygen levels in our atmosphere - allowing multicellular life to flourish.
The world has about 130 crater structures of possible impact origin. The Vredefort Dome is the oldest and largest of these, clearly visible to satellite cameras.
The original crater, now eroded away, was probably 250 to 300 kilometres
wide. It was larger than the Sudbury impact structure in Canada, which is about 200km in diameter.
At 2-billion years old, Vredefort is far older than the Chixculub structure in Mexico which, with an age of 65-million years, is thought to be the site of the meteor impact that led to the extinction of the dinosaurs.
Vredefort's original impact scar measures 380km across and is made up of three concentric circles of raised rock. They were created by the rebound of rock below the impact site when the asteroid hit. Most of these structures have eroded away and are no longer clearly visible.
The inner circle, measuring 180km, is still visible and can be seen in the beautiful range of hills near Parys and Vredefort. In 2005, Unesco - the United Nations Educational, Scientific and Cultural Organisation - named this area of the Vredefort Dome a World Heritage site.
Internationally, there are 851 World
Heritage sites, in 141 countries. Africa has 77 sites and South Africa a total of eight - four cultural, three natural and one of mixed cultural and natural heritage. The Vredefort Dome is a natural heritage site.
South Africa's other World Heritage sites are Robben Island, the Greater St Lucia Wetlands Park, the Mapungubwe Cultural Landscape, the Cradle of Humankind, the uKhahlamba Drakensberg Park, the Cape Floral Region and the Richtersveld Cultural Landscape.
The Vredefort Conservancy
In 1937, earth scientists John Boon and Claude Albritton Boon were the first to suggest that the Vredefort structure was the scar of an ancient meteorite impact. Since then the site has been studied extensively by earth scientists from around the world.
The Vredefort Dome Conservancy, as it is now known, is not just of scientific value. It also has great scenic beauty, making it an ideal tourist
The Dome Conservancy contains a finely balanced ecosystem made up of open plains, bushveld, mountains and ravines with abundant flora and fauna. At least 99 plant species have already been identified, of which the world's largest olive wood tree forest is probably the best known.
It is also an important birding area, with over 450 species already identified. It also has as many identified butterflies as the whole of Great Britain, and is home to rare animals such as the rooikat, aardwolf, leopard and the endangered rock dassie.
The Vredefort Dome site fulfils all the criteria set by Unesco for a World Heritage site. It is of outstanding universal value from a scientific point of view, and is remarkable evidence of an important moment in the earth's geologic history.
Updated December 2015
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