An impact the size of the Vredefort event – if it happened again – would be a global catastrophe. The shock wave, firestorm, tsunamis and dust cloud generated by the blast would wipe out most life on earth, with the possible exception of bacteria, insects and some creatures living underground. Vredefort did not cause a mass extinction because at the time the only forms of life on earth were bacteria, which survived.
Later on, other creatures were not so lucky. We have evidence in the rocks as to what happened at Chicxulub, Yucatan, proving that mass extinctions are likely when a big impact occurs. But what seems a catastrophe to us is merely the universe going about its normal business, smashing things together or blowing them apart. We are just caught in the crossfire.
Some 65 million years ago a large asteroid struck the Yucatan Peninsula, Mexico. The event is famous for finishing off the dinosaurs, but many more creatures also died off.
The Chicxulub asteroid, perhaps 11km across, travelling at 20km a second (72 000km/hr), delivered a destructive blast millions of times more powerful than the combined yield of all the world’s nuclear weapons. It set off earthquakes greater than 11 in magnitude and threw up widespread tsunamis, while dust shrouded the globe for years in a dense layer of debris.
What happens in a catastrophe impresses best where its evidence is real. Evidence for the impact was found in 1981 by the physicist Luis Alvarez and his son, geologist Walter Alvarez (pictured), as far away as Italy where a thin layer of carbon in the rocks provided tell-tale evidence of a global catastrophe. Since their discovery, other scientists have confirmed that the evidence is more or less conclusive: this was not a killer volcano but an asteroid.
Known as the Chicxulub Crater, which lies half in the Caribbean sea and half on land, the impact is generally thought to have caused the extinction of numerous animal and plant groups, including non-avian dinosaurs. The layer marks the so-called K-T boundary (Cretaceous-Tertiary extinction event). Beneath it, fossils show abundant life forms. Above it there is nothing, until life regenerates again.
Will it happen again? Yes, almost certainly. Big impacts like Chicxulub and Vredefort happen rarely (the probability calculation is one every 100 million years, but that doesn’t mean one couldn’t happen tomorrow).
Scientists like the Alvarezes and Eugene Shoemaker (father of impact studies) have given rise to modern ideas of “catastrophism” – the analysis of disasters. Major catastrophes include meteorite impacts, earthquakes, volcanoes, tsunamis, hurricanes, floods and devastating wildfires, all of which we have seen in our lifetimes.
The study of catastrophes crosses two key disciplines: biology and geology, as great extinctions leave traces of earlier life in the rocks.
But far more is involved in identifying the causes of catastrophes. For one thing, we want to be able to predict when they are likely to happen, and take evasive action. In Roman times, the people of Pompeii had little warning of the eruption of Vesuvius and were caught offguard when lava swamped their city, swallowing many of them up in agonising deaths. Not only do we want to forecast catastrophes but Emergency Services need to be prepared for rescue and medical assistance.
By studying meteorites, we can learn details about how our solar system evolved into the Sun and planets of today – and how meteorite impacts could affect our future. Our survival on Earth (or any other body we may live on in the future) depends on knowing what we may face and being equipped to handle it.
Catastrophism is merely our perspective on “normal” processes in the universe. Stars explode as supernovae; black holes devour galaxies; in solar systems, planets collide and fragment (the asteroids may have formed this way, while the Earth lost its lighter rocks to the its Moon and gained its iron core in a collision between the two in the earliest times of their formation). Great extinctions have been a feature of Earth’s past, and research reveals that our planet is dotted with asteroid / comet craters. Earthquakes, volcanoes, tsunamis are natural phenomena, nothing out of the ordinary!
How then do we develop our understanding of catastrophes? The sciences involved in this multi-disciplinary quest cover most of what we know, from A to Z, astronomy to zoology. Evolution teaches us how sudden disasters disrupt life and accelerate natural selection: it is not only the fit that survive, but the lucky who happen to be out of the way when Jove hurls his flaming bolts. The predecessors of all mammals today were probably mice-like creatures living in tunnels when the dinosaurs met their end on the surface.
Geologists trace fossil evidence of catastrophes in the rocks and pinpoint the structures that show major changes over time. Just so will future geologists (if there are any) find a layer of plastics on what are now ocean floors, carried there by rivers and dumped as microns or nurdles beneath the waves. Climatologists warn us that we are destroying our own habitat and creating the Sixth Mass Extinction in Earth’s history with pollution, habitat degradation and global warming. Mathematicians use fractals to find smaller and smaller repeating patterns in chaotic evidence, and calculate how much time we have left to correct our destructive ways. Risk managers in business might be wise to take all of this into account when making investments in a sustainable future.
Visit the sites
In South Africa we are fortunate to have many impact craters, still visible due to the fact that our subcontinent is geologically fairly stable and inert. Vredefort, Tswaing, Morokweng, the Hoba meteorite in Namibia and several other localities offer scientists the opportunity to study impact craters, and give the general public the chance to visit and see them. Craters shape landscapes and therefore affect life on Earth.
The holistic approach to catastrophe is a developing field of research. To see how it applies, get our booklet and self-drive guide to the Vredefort Dome. It covers not just on the impact but Stone Age & Iron Age archaeology, battlefields, mining history, and the cultures that have flourished here. Personalities ranging from Mzilikazi to Rhodes, General de Wet and Mandela have all had a hand in the Dome story.