An asteroid discovered in Sweden is "unlike anything ever found" - and might be a key to unlocking the mystery of how life developed on Earth.
The rock is one of about 100 fossilised meteorites which have been extracted from a limestone quarry near to Stockholm.
This cache of meteorite fragments dates back about 470 million years ago, when Earth experienced a sudden burst of new species. Prior to this time Earth also experienced ten to hundreds of times more meteor strikes than it does now, and the event often used to explain the coincidence is a big asteroid collision between two huge rocks somewhere between Mars and Jupiter.
The theory suggests that the sudden rise in strikes might have kick-started the evolution of new species and animal types, by opening up new niches to be exploited, and killing off certain species to make way for new ones.
Most of the remains of these meteorites are iron-poor 'L chondrites'. This suggests they come from the same asteroid involved in the large-scale collision.
But one of the rocks found in the Stockholm quarry is not. This rock dates to the same time but is of a type totally unknown to science.
According to Lund University, the odd, rarer meteorite might be a piece of the second asteroid which collided in space and then rained its fragments down on Earth.
The find is crucial because it might lend evidence to the theory that it was this strike in deep space which provided the necessary 'boost' in evolution which eventually led to the rise of the dinosaurs and -- indirectly -- us.
The study is published in Earth and Planetary Science Letters and a thorough analysis can be found at New Scientist.