Gosses Bluff

Gosses Bluff is an impact crater, located west of Alice Springs and south of the Macdonnell Ranges, in the arid Missionary Plain in the Northern Territory. The bluff itself is a circular ring of hills 5km in diameter and 200m high, in the centre of a crater. It was formed 142 million years ago by the impact of an asteroid or comet up to 2km in diameter. The hills are part of the crater's central uplift, which formed when the earth's surface recoiled from the impact. A circular drainage system 24km in diameter marks the outer ring of the crater. The bluff is deeply significant to the Western Arrernte Aboriginal people, who own the Tnorala Conservation Reserve that contains the crater.

This impact is believed to have occurred at the very end of the Jurassic Period at a time when the largest dinosaurs, the sauropods, declined in number. This impact alone would not have been large enough to cause mass extinctions on a broad scale, but would certainly have caused a lot of local damage. The Morokweng crater in South Africa dates to roughly the same time period, although at 70km in diameter was a much larger impact than that which created Gosses Bluff.

It is estimated that each year the Earth receives about 100,000 tonnes of material from space. If this mass all arrived at once it would be a catastrophe! Most of it comes in meteor showers and is burned up by friction with air molecules in the upper atmosphere: a "shooting star" is a meteoroid either burning up or just grazing our atmosphere. These objects may approach Earth at speeds up to 70 km per second! The hundreds of impact craters on the earth's surface were caused by asteroids or comets colliding with our plant.

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Around twenty four impact craters are known in Australia, ranging in size from less than 20m in diameter to perhaps more than 100km. Some date back hundreds of millions (even billions) of years. Others are as recent as just a few thousand years old. Most probably did little more than localised damage. At least two Australian impacts may have contributed to mass extinctions.

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