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8,000-year-old petroglyphs found in earth's largest meteor crater

Leading South African scientists from the University of the Free State are about to undertake research into the destruction caused by a huge ancient meteorite that could hold clues critical to the history, mechanisms and consequences of meteorite strikes on earth and elsewhere in the Solar System. The results of this work could mean a better understanding of the effects of such impacts and the greater safety of the earth.

8,000-year-old petroglyphs found in earth's largest meteor crater
One of the carvings found on the impact crater dyke [Credit: University of the Free State]
The vast crater is also fascinating for its human interest from early man who used it as a centre of cultural importance and left rock carvings as proof of their presence. The site was of great spiritual significance, comparable to the stone circles of Stonehenge in the UK. The Khoi-San patently understood that the rock remains found on the surface were unique and important.

The University of the Free State is fortunate to be situated only 180 miles from the largest meteorite crater, which has an initial diameter of 300 kilometers (186.4 miles) and at over two billion years old is the oldest impact crater on Earth – known as the Vredefort impact structure. The meteorite that made the impact was travelling at 70,000 kilometres (43,495.98 miles) per hour when it struck the earth.

The effect on the earth has lasted millennia in a dynamic, changing process. The recent meteor impact discovery in Scotland is tiny by comparison. Had man been present at the time of the Scottish impact it would have destroyed the whole Scots community, whereas the Vredefort impact would have led to human extinction on earth.

Carving appears to show a horse [Credit: University of the Free State]
The University of the Free State study of the Vredefort impact structure will look in particular at the Granophyre dykes, the only remnants of the now eroded impact melt sheet that intruded downwards through fractures in the crater floor.

Gold in the Crater

In addition to the planetary-scale importance of impact events, some impact craters are connected with ore deposits. The Vredefort impact structure in South Africa is situated in the center of the Witwatersrand goldfields, and the richness, location, and accessibility of the gold mineralisation are clearly connected to the impact structure, which moved the gold deposits around, concentrating it, say the UFS scientists studying the crater. The impact structure, therefore, influenced economic interest in the area, and as a result created the city of Johannesburg, one of the largest cities on the African continent.

An international team of scientists is being led by principal investigator Dr. Matthew S. Huber of the University of the Free State in Bloemfontein, Faculty of Natural and Agricultural Sciences, Department of Geology, who says: “As impact events can potentially represent a threat to life with the ability to alter the development of entire planets, it is critical that we develop a better understanding of their history, mechanisms, and consequences. By studying the traces of impact events on Earth, we can reconstruct the mechanisms of such processes, and gain greater understanding of our own ecosystem and origin.”

8,000-year-old petroglyphs found in earth's largest meteor crater
Carving found in the Vredefort impact crater [Credit: University of the Free State]
He adds: “The Vredefort impact was massive – it was larger than the impact that killed the dinosaurs. If it happened today, civilization might be at an end. We only know of three such impact craters preserved on Earth: the Chicxulub crater that killed the dinosaurs, the Sudbury crater in Canada, and the Vredefort crater. What is really unique about Vredefort is that we get to see the deep architecture below these massive impact craters, and those deep rocks tell not only the story of what happened at the moment of impact, but also how those rocks adjusted and shifted for thousands of years after the impact.”

“We are pretty sure that the asteroid that caused the Vredefort impact event was about 10-15 kilometres (6.2-9.3 miles) in diameter. Many space programs around the world are tracking asteroids that are potentially dangerous to life on Earth. These programs have discovered that there are hundreds of asteroids that are at least 1 km in diameter that would cause massive devastation if they impacted the earth. Fortunately, at the moment, none of these asteroids appears to be on a collision course with us!”

And on the subject of early man’s link to the crater, he says: “We suspect that one reason the San took interest in the crater’s Granophyre dykes was that the dyke resembles the shape of the Rain Snake. The location of the dyke on top of a hill, near a body of water, and in the shape of an important deity probably brought them there so that they could perform rainmaking rituals, and possibly other important cultural activities. We hope that detailed investigation will show us more about how the site might have been utilised.”

8,000-year-old petroglyphs found in earth's largest meteor crater
Image showing a hippopotamus carved by the San people around 8,000 years ago
[Credit: University of the Free State]
Observations of rocky bodies such as the Moon, Mars, and asteroids have revealed that impact craters are common throughout the Solar System. Meteorite impacts have also left scars over the surface of the Earth, and some of these impact events have had major effects on our planet. A powerful meteorite impact 65 million years ago, known as the Chicxulub impact event, led to the extinction of 65% of life on earth, including the dinosaurs.

On Earth, erosion and active plate tectonics remove meteorite impact craters from the surface comparatively quickly. When impact craters are exposed at the surface, they are often utilised by people living in the area for cultural purposes.

The structure is easily accessible for sampling and research, providing an opportunity to study this impact crater. Vredefort is an ideal impact structure to study, as it is deeply eroded, showing features not seen elsewhere on Earth, is accessible at the surface, and has not been modified by any major tectonic event, due to its position on the stable Kaapvaal craton. Additionally, it has cultural significance, with early man, Khoi-San rock art, rock shelters, pottery, and engravings. This provides opportunities to enhance knowledge of South Africa’s “First Peoples”.

8,000-year-old petroglyphs found in earth's largest meteor crater
Some of the crater's multiple rims have eroded away, but from space, what is left is clear
[Credit: University of the Free State]
Research Objectives 

The University of the Free State will combine geological investigations with cultural investigations to provide a unique perspective on the Vredefort impact structure that is both scientifically advanced and grounded in humanity.

UNESCO World Heritage Site

The Vredefort impact structure is a UNESCO world heritage site, based on its socio-cultural, aesthetic, conservational, historical and scientific significance. In addition, this site has traces of San rock art indicative of material remains attached to a specific socio-cultural reality. These rock art sites form an integral part of the South African cultural heritage landscape.

Granophyre Dykes

The proposed University of the Free State study of the Vredefort impact structure will look in particular at the Granophyre dykes, the only remnants of the now eroded impact melt sheet that intruded downwards through fractures in the crater floor. Because the impact melt intruded downwards, capturing rock fragments on its way, it can provide samples of rock formations that are long eroded and are otherwise not accessible.

8,000-year-old petroglyphs found in earth's largest meteor crater
Granophyre dyke [Credit: University of the Free State]
Such samples allow observations of shock microstructures, formed in target rocks that were located near the earth’s early surface at the time of impact. Studying the granophyre dykes can answer many geological questions. The overarching questions the UFS research team want to answer are: 1) what did the Vredefort structure look like? And 2) what was it composed of before it was eroded?

These dykes, exposed by erosion, have been exploited by the Khoi-San culture as ceremonial sites, so from a heritage perspective, the above stated objectives offer great potential to contribute also to the existing body of knowledge of the scientific and aesthetic significance of this heritage site.

By studying the impact structure at both macro- and micro-scales, the UFS team will make important contributions about the knowledge of impact craters, the processes that take place during large impact events, and processes and outcomes attached to the scope of heritage.

8,000-year-old petroglyphs found in earth's largest meteor crater
Image showing the outline of the dyke where the carvings were found
[Credit: University of the Free State]
These geological observations and results can then be applied to other planetary bodies, giving us a greater understanding of the Moon, Mars, and other planets. In terms of the heritage scope, our outcomes will contribute to the body of anthropological knowledge on the socio-cultural reality of the Khoi-San within the Free State as well as the concept of “living” heritage.

Anthropological literature on the San is limited to the South African Provinces of the Western Cape and the Northern Cape, as well as countries such as Botswana and Namibia. Anthropological understanding of the San in the Free State and specifically in relation to the concept heritage is lacking.

Expected results of the Project

The new data generated from this project will help the team to constrain the stages and processes that occurred during the formation and subsequent development of the impact structure. This data will fill in gaps in the scientific literature and have global implications, with results being applicable to not only other impact structure on Earth, but also on the Moon and Mars.

The work will grow the scientific understanding of impact-cratering processes. It will furthermore contribute to the scholarly understanding of the heritage significance of this site with specific reference to the Khoi-San.

Source: University of the Free State [June 13, 2019]


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