The biggest meteor known to collide with Earth?

What’s the biggest meteor that we know of that hit the Earth? And when and where did it hit the Earth?

Computer models suggest that, early in Earth’s history, a piece of debris not much less massive than Earth might have slammed into us and created Earth’s moon. But there’s no direct evidence for this collision and records of recent impacts are also hard to find.

Winds and rain fill in craters and erode crater walls, jungles blanket them, and lava flows pave them over. Earth’s tectonic plates move and alter the land. It’s not surprising that, despite thousands of craters seen on Mars and the moon, scientists know fewer than 180 impact craters on Earth.

Map of all the confirmed impact craters on Earth (click to enlarge image)
Map of all the confirmed impact craters on Earth (click to enlarge image)

Of these, Vredefort Crater in South Africa is probably the biggest. The crater’s about 300 kilometers or 200 miles across. It’s thought to be about two billion years ago. The size of the crater depends on the speed and size of the incoming rock. But scientists think the crater was made by a chunk of space debris about 20 kilometers, or 12 miles, across about the length of Manhattan Island.

The Vredefort structure – The world’s largest and oldest meteor impact crater

The origin of the Vredefort Dome, a 70 km-wide uplift structure located some 120 km southwest of Johannesburg in the central part of the Witwatersrand Basin, has been debated heatedly for much of this century. Most South African geologists have long favoured an internal, tectonic or so-called ‘crypto-explosion’ origin, but the spectacular deformation phenomena of the Dome, such as melt breccias, as well as the mineralogical and geological evidence presented since 1994, have now convinced the majority of researchers of an origin by catastrophic impact of a large extraterrestrial projectile.

Detailed dating of geological material in the area has provided a precise age of 2 020 ± 5 Ma – not only separating the age of the impact event from the time of the emplacement of the Bushveld Complex at 2 060 Ma ago, but also identifying Vredefort as the oldest known impact structure on Earth.

It has been shown convincingly that the original size of the impact structure could well have been 250 km in diameter, or even larger. This makes Vredefort the largest known impact structure on Earth and indicates that the whole extent of the Witwatersrand Basin coincides with the – admittedly now deformed – impact ring basin around the central uplift feature, the Vredefort Dome. In fact, structure and geometry of the Basin and Dome coincide remarkably well with the characteristics of such a large, complex impact structure.

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