Almost all of us own a piece of space rock. Or at least, almost all of us us who are married do.
It's true. Your wedding ring ? if it's gold or platinum ? almost certainly did not start its life on Earth. Four and a half billion years ago, when our planet was forming out of the swirling disc of debris that was the solar system, your jewellery was nowhere to be seen; it arrived hundreds of millions of years later, in a cataclysmic bombardment of asteroids. Or so scientists believe.
There would have been lots of gold in the forming earth, but because our nascent planet was molten rock at that stage, the heavy materials would have sunk to the core, and gold and platinum are among the heaviest naturally occurring elements. But, around four billion years ago, the moon was subjected to a violent series of large space strikes, as revealed by the craters on its surface and radiometric dating of rocks brought back by the Apollo missions. In 2011 a University of Bristol team found evidence that the crust of earth is partly formed of similar rocks. The period when all this was happening is known as the "late heavy bombardment", and it's believed that this is what delivered almost all the heavy metals in the earth's crust, including gold, tungsten and platinum.
Artwork depicting the Late Heavy Bombardment (Chris Butler/Space Photography Library)
I'm writing this because it was reported the other day that the meteor that exploded over Russia last week has sparked a "gold rush", as excited collectors hunted for pieces of the rock. One has appeared on a Russian auction site at a price of ?6,500. There should be plenty to find: Nasa researchers have now said that the meteor was far larger than originally thought, about 55 feet across and weighing around 10,000 tons, the biggest object to hit the earth since 1908. Despite the extraordinary force with which it smashed into the atmosphere (it exploded with the energy of 30 Hiroshima bombs), plenty of fragments should have made it to the ground.
The sprint for debris reminds us just how fascinated with space rocks we are. The actual content of the meteor will, most likely, be nothing particularly exciting: early reports suggest that they're chondrite, a mineral mix containing about 10 per cent iron. But the simple fact that it is not of this earth makes meteor-stuff appealing. Rich collectors, including Steven Spielberg and Nicholas Cage, will spend thousands of pounds on small fragments: ?10,000 an ounce is fairly standard, according to the Macovich Collection of Meteorites, and for a lunar meteorite, blasted off the face of the moon by one of those ancient collisions, it could be five times that.
But the fascination is ancient. Anyone who's ever read a fantasy novel knows that "star iron" makes the best magic swords ? but it isn't only the stuff of sub-Tolkien imaginings. In pre-Iron Age civilisations, which were unable to smelt iron ore, the only source of pure iron ? which made far better weapons and tools than soft bronze or copper ? was meteor fragments. The Assyrians called iron the "metal of god" or "of heaven", and in ancient Egypt it was known as "bia-en-pet", or "thunderbolt of heaven". A dagger made from meteoric iron was found in Tutankhamun's tomb; for centuries the Inuit used harpoons made from iron from a giant meteorite that fell in Greenland.
The connection between heavenly fireballs and heaven ? and the judgment of God ? is old, as well. A clergyman in the Russian town of Chebarkul, where a hefty piece of the meteor is believed to have fallen (government divers are searching the bottom of a local lake as I write this), said that "with all of this, God is warning us of the end times". Most of us nowadays might not subscribe to that view ? although there was something apocalyptic about the footage of the great fireball streaking towards earth, like the beginning of an alien invasion movie ? but in the earlier centuries, the idea was more widespread. Zoroastrian prophecies from 500BC predict that the world would end when a comet, hurled by Satan, crashed into the earth; both the Book of Revelation and the Old Testament talk about rains of fire from the skies.
Anyway. We don't think of meteors as harbingers of Armageddon any more (most of us), and we don't need them to forge weapons for battle. But I quite like the knowledge that my wedding ring, and my late grandmother's ring which my wife now wears, hurtled out of the sky in a howling ball of flame four thousand million years ago. When someone asks "Where does it come from?", it's a better answer than "a jewellery shop in Stowmarket", anyway
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