Meteor strike a 'wake-up call for humanity'
A meteor that exploded over Russia in February was 20 metres in diameter and caused a blast equivalent to 600,000 tonnes of TNT, according to scientists studying the event.
The space rock blew apart 18.5 miles above the city of Chelyabinsk, briefly outshining the sun and inflicting severe burns on a number of observers.
It was the largest object to hit the Earth since the Tunguska event of 1908, when an exploding comet or asteroid destroyed 2,000 square kilometres of Siberian forest.
Analysis showed that the rock was a common type known as a 'chondrite' – the kind most likely to cause a major extinction event in the future.
Professor Qing-Zhu Yin, from the Department of Earth and Planetary Sciences at the University of California, said the meteor strike was a "wake-up call".
He added: "If humanity does not want to go the way of the dinosaurs, we need to study an event like this in detail."
The Chelyabinsk object entered the Earth's atmosphere at just over 19 kilometres per second, slightly faster than had previously been reported.
Three-quarters of the rock evaporated in the explosion, said the researchers, whose findings are reported in the journal 'Science'.
Most of the rest of the object became a glowing orange dust cloud and only a small fraction – still weighing 4,000kg to 6,000kg – fell to the ground.
The largest single fragment, weighing about 650kg, was recovered from the bed of Lake Chebarkul in October.