Photo by Jimmy Conover on Unsplash.
An astrobleme is the name given to a site that’s been hit by a meteorite. Or, to put it in more science-y terms, an ‘impact structure’. This isn’t to be confused with an ‘impact crater’ which is, well, just the hole-y bit – the impact structure includes all the deformed bedrock and sediment that’s underneath the hole (assuming I’ve understood Wikipedia correctly of course).
I like the word ‘astrobleme’ because it’s super literal. Its etymology translates as ‘star wound’ – ‘astron’ is Greek for star, and ‘bleme’ (also Greek) means ‘throw of a missile; wound caused by a missile’. It was coined by an American geologist called Robert S Dietz (1914–1995). His most notable feat was identifying the Sudbury Basin (Sudbury in Ontario, Canada, not the one in Suffolk which is just up the road from where I type this) as an ancient astrobleme – the second (or third, depending on which website you look at) biggest in the world.
But what’s the biggest, I hear you cry? Well, that honour belongs to the Vredefort crater in South Africa. It’s just over 300km (186.4 miles in old money) across. That means that the meteor that hit it was over 15km (9.3 miles) in diameter. Don’t panic though – it happened a VERY long time ago in the Paleoproterozoic Era which was between 2,500 and 1,600 million years ago.
The Vrefort crater has competition for the top spot from the Wilkes Land crater, which is underneath the ice caps in Antarctica and is as yet unverified. If it is an astrobleme then it’s a massive 480 km (300 miles) across. That means that the meteorite that caused it was at least 55km (34.5 miles) in diameter, which is four or five times wider than the Chicxulub impactor (good name for a band) AKA the one that killed all the dinosaurs, and also three-quarters of all the plant and animal species on Earth. Fuck.