The first crater on Earth to have been recognized as an impact crater - a crater caused by the impact of a meteor - is Meteor Crater in Arizona.

It is also known as Barringer Crater.

The saucer-shaped crater, located in the desert near Arizona's Canyon Diablo is 1,265m (4,150ft) in diameter. Its maximum depth is 175m (575ft) deep.

According to current estimates, the meteor that struck the Arizona desert and caused the crater to form weighed 300,000 tons and had a diameter of 46m (150ft). It is believed to have been traveling at a velocity of around 43,000kph (27,000mph).

The collision probably occurred around 50,000 years ago.

Evidence of the Impact

Meteor Crater was originally thought to be a volcanic crater, since there were other volcanic craters, including the still-active Sunset Crater, in the region.

However, in the 1890s, mineralogists discovered iron fragments in the crater. This led geologists to suggest that the crater was caused by a meteor crash.

Daniel Barringer (1860-1929), a Philadelphia mining engineer who explored the site in 1903, was convinced the meteorite was buried beneath the crater. He purchased the land and, in 1906, began drilling.

Barringer and his team discovered enough iron and nickel-iron fragments to persuade the scientific world that the crater was probably formed by a meteor.

During the 1930s, around $400,000 was spent on drilling bores into the floor of the crater. Fragments of nickel-iron believed to have come from the meteorite were found at depths of 260m (700ft). Below this, the rock was undisturbed.

All attempts at finding the core intact below the crater have been abandoned. Scientists now believe the meteor exploded on impact, and that much of its material vaporized into the air.

The millions of nickel-iron grains discovered at the site are thought to have condensed from a hot metallic cloud that resulted from the blast. In addition, individual nickel-iron fragments as heavy as 640kg (1,400lbs) have been found scattered over an area of (100 sq.mi).

In 1960, scientists discovered coesite and stishovite at the site. These two rare forms of silica can only be created when the temperature and pressure is very high. These conditions would have been created when a meteor crashed into sandstone desert. This was proof that the crater was formed by a meteor.