The Largest and Oldest
The meteorite impact that happened in the Free State made a crater that was about 300 km wide (from Johannesburg to Welkom!). This is the biggest meteorite impact that geologists have yet found on Earth and it is nearly twice as big as the impact that killed the dinosaurs 65 million years ago. This makes it a site of great importance for scientists. It is also the oldest impact crater that has been found on Earth. It is mainly for these reasons that it has been made a World Heritage Site.
Over many decades, geologists from South Africa and other parts of the world have been studying the broken and melted rocks around Parys and Vredefort to understand this Vredefort Impact Even.
- The meteorite impact happened about 2023 million years ago, at a time when there were no people or even animals of plants like we see today. The only living thing was a type of algae, like the green slime seen in dams today.
- To make a crater 300 km wide, the meteorite must have been about 10 km across (as big as a mountain) and travelling at more than 10 km per second (36 000 km/h!).
- The Vredefort Dome is only the central part of the impact crater. It is called a dome because the rock layers were bent into the shape of an upside-down bowl 90km across by the impact.
SHOOTING STARS AND METEORITE IMPACTS
If we look up into the sky on a dark night we often see “shooting stars”. These are bright streaks of light that move very fast across the sky for only a few seconds before they disappear. They are not real stars – the streaks of light are caused by tine pieces of burning rock, flying faster than bullets that enter Earth’s atmosphere from Outer Space. Because they are moving so fast (more than 10 km per second, which means they would take 30 seconds to fly from Parys to Bloemfontein!), when they enter the atmosphere they start to burn. (This burning is caused by friction with the air. When you rub your hands together very fast, they also get hot. To melt rock, though, the temperature must reach more than 1000 °C!)
There are many, many millions of such small pieces of rock in Outer Space, left over from when our Sun and the planets were formed. Thousands of them become shooting stars every day. But among them are also larger pieces of rock, ranging from football size to some up to many kilometers across. These asteroids also sometimes fall into the Earth’s atmosphere, but not as often as the smaller pieces. When they do, they are too big to burn up or slow down and so they hit the ground at very high speed. An asteroid that hits the Earth is called a meteorite. Thousands of small meteorites have already been found around the world.)
The damage caused when a meteorite collides with the Earth is massive. The speed of a meteorite is so high that is explodes when intense heat of many thousands of degrees Celsius that can even melt rock. In this way, the meteorite itself is completely destroyed. This is what happened in the Free State near Parys and Vredefort millions of years ago. The explosion was so great that it was many millions of times more powerful than the biggest atomic bomb ever built on Earth. If it happened today it would kill almost all living things on Earth, including most people.