Ian Halliday of Ottawa's Herzberg Institute of Astrophysics estimates that 5,800 meteorites weighing at least 100 grams (3.5 oz) land on Earth each year.

An object 10 kilometres (6.2 miles) across and travelling at a velocity of 50 km (31 miles) per second is estimated to strike once every hundred million years. Every million years, we can expect an asteroid 1 km (0.6 mile). There are more than 2,000 asteroids of that size or greater in Earth-crossing orbits. The first, Apollo, was discovered in 1932.

In 1994, two American scientists, Clark Chapman and David Morrison, published calculations in the journal Nature that suggested that our chance of being killed by a cosmic collision was 1 in 20,000 — similar to the risk of dying in a commercial plane crash.

• On 12 February 1947, the second-biggest meteoroid of the 20th century — known as the Sikhote-Alin meteoroid — exploded at a height of 6-8 km (3.7-5 miles) over mountains in south-eastern Russia, about 375 km (233 miles) from the port of Vladivostock. The 70-tonne iron created 122 craters over an area measuring 2 km by 1 km (1.2 by 0.6 miles). The largest lump found weighed 2 tonnes.

• In November 1954, Anne Hodges was struck on the hip when a 3.9 kg (8.6 lb) stony-iron meteorite tore through the roof of her home in Sylacauga, Alabama. She suffered nothing worse than bruising.

• On 21 June 1994, José Martin was driving from Madrid to Marbella when a meteorite weighing 1.4 kg (3 lb) crashed through the windscreen and injured his finger. More than 50 other fragments were found within 200 metres (656 feet) of his car.

Near misses

• On 30 June 1908, a fireball exploded over the Podkamennaya Tunguska river basin in Siberia, destroying 3,000 sq. km (1,158 sq. miles) of forest. The blast — known as the 'Tunguska Event' — was caused by the disintegration of a stony object — about 100 m (328 ft) across at an altitude of 6-10 km (3.7-6.2 miles) — with the power of 10-15 megatons of high explosive.

  Because the area was so sparsely populated, only two related human fatalities are recorded, although thousands of reindeer came off badly. A man called S B Semenov, who had been less than 100 km (62 miles) away at the time, described the event: 'I felt a great heat as if my shirt had caught fire … there was a bang in the sky … I was thrown to the ground about three sazhen [5-6 m/16.4-19.7 ft] away from the porch and for a moment I lost consciousness.'

• In 1937, the asteroid Hermes, measuring 1 km (0.62 mile) across, sped past the Earth at a distance of around 700,000 km (434,970 miles), prompting a headline in the Sunday Graphic newspaper: 'World disaster missed — by 5 hours.' One South African astronomer was quoted as saying: 'It was the nearest thing to a collision between the Earth and another body that has ever happened.'

• In April 1972, a fireball shot across the sky 55 km (34 miles) above Montana before zooming out into space again over Edmonton in Canada. It is thought to have been caused by a cosmic body larger than the Tunguska meteoroid.

• In February 1994, a fiery meteoroid with a mass of 1,000 tonnes, travelling at 72,000 km (44,740 miles) per hour, exploded 20 km (12.4 miles) over the sea near Tokelau in the south Pacific. It was detected by US spy satellites. Fisherman described is as being almost as bright as the Sun.

Antarctic bounty

Between 1969 and 1999, 20,000 meteorites were found in the Antarctic, most no bigger than oranges. This glut is due to two facts: meteorites show up nicely on the ice, and there has been a concerted search for them by scientists. For instance, in 1988-9, eight people found 1,078 meteorites in six weeks.

Most meteorites have been discovered in the so-called 'blue ice' areas. As the ice cap moves north, it sometimes comes up against a mountain barrier of ice that slows it down. When this happens, polar winds blow away the surface ice and older layers rise up, exposing old meteorites in the process.

Martian meteorites

Meteorite ALH84001 was discovered in the Allan Hills of Antarctica in 1984. When analysed properly, its composition turned out to be quite similar to material from the Martian atmosphere that had been chemically measured by the Viking landers in 1976.

NASA scientists believe that ALH84001 was catapulted from Mars when that planet was itself hit by a meteoroid, and it eventually found its way to Earth 13,000 years ago. The scientists announced that miniscule Martian microfossils had been found within the meteorite, giving rise to speculation about the possibilities of 'life on Mars'. However, other boffins have since cast doubt on this finding.

A fragment from a meteor shower that struck the Egyptian town of Nakhla in 1911, killing a dog, is also thought to have originated on the red planet.