Why do people talk about a ‘meteoric rise’, when what meteors do is fall? Very odd.
Recently I had the great pleasure of visiting Meteor Crater, Arizona, an enormous hole in the ground that’s not far from another famous hole in the ground, the Grand Canyon. If you ever visit the latter, I highly recommend taking a slight detour to see the former.
Meteor Crater – a very matter-of-fact name – was formed about 50,000 years ago by a meteorite 50 metres across and weighing around 300,000 tons, releasing 10-20 megatons of TNT. That’s about the same force as a hydrogen bomb.
The crater was known to Native Americans, but the earliest historical record of it is from 1871. Early studies concluded that it was a volcano, but in 1902, meteorite-proponent Daniel Moreau Barringer acquired it, with an intent to mine it for iron.
The idea that rocks or anything else could fall from the sky was initially very controversial. People laughed at German physicist Ernst Florens Chladni, who in 1794 was the first person to suggest the idea. But he was vindicated in 1795, when a 25 kilogram stone fell in broad daylight in Wold Cottage England. Some were still sceptical though, notably the French Academy of Sciences; until 1803, when about 3,000 meteorites fell on France. That pretty much shut them up.
Now it’s important to get some terminology right here: a meteorite is the rock or mineral that actually hits the ground. Meteor is what it’s called when it’s flying through the sky, aka a shooting star. And when it’s merely a rock floating in space, it’s a meteoroid, unless it’s really big, in which case it’s an asteroid.
Barringer was far from the first to try and exploit meteorites for their iron. Before people learned how to smelter ores they were the main source of iron for tools and the like.
Overall though, fewer than 10% of meteorites are iron-nickel like the one that hit Arizona, or that formed the Wolfe Creek Crater in Western Australia (0.87 kilometres across and up to 300,000 years old, one of 27 Australian meteorite craters listed in the Earth Impact Database, mostly in Western Australia and the Northern Territory). They’re believed to come from cores of asteroids that have broken up, which explains their rarity.
Most other meteorites are a stony material called chondrite, made of small round particles called chondrules. These are thought to be rock formed at the birth of the Solar System.
Some (about 4.6%) contain carbon and are known as carbonaceous chondrites. These sometimes include organic compound and are eagerly sought, like the one that hit California on 22 April 2012.
With so many rocks bombarding the planet, and giant impact craters like that in Arizona, they’ve got to be pretty dangerous, right?
Lost in Science 