The Chicxulub Impact

The asteroid or comet whose collision with Earth is thought to have killed off the dinosaurs kicked up a monumental mess in its wake.

It is believed that in one second the 10-kilometre-wide body dug a hole 13 kilometres deep.

The impact created an explosion equal to that caused by 100 million megatons of TNT - something like 500,000 times the size of the largest nuclear bomb ever set off, the Tsar Bomba.

The collision would have produced shock waves with a pressure of about 660 gigapascals, a pressure greater than that in the centre of Earth. The collision has been dated to about 65 million years ago, a time when the dinosaurs as well as many other groups of animal inexplicably died in massive numbers.

In the 15 years since the idea first was put forward, scientists have increasingly come to believe that the demise of the dinosaurs - as well as other large-scale die-offs of animals at earlier periods - was an environmental consequence of comet or asteroid impacts.

 
Northwest corner of Yucatan Peninsula generated from Shuttle Radar Topography Mission (SRTM) data-indication of the Chicxulub impact crater (c) Source: nasa.gov

Chicxulub impact crater trough and sinkhole (c) Source: nasa.gov

Image showing the 4 rings of the Chicxulub crater at the Yucatan Peninsula (c) Source: ndsu.edu

 
Examples of an unshocked quartz grain (left)
and a shock-metamorphosed quartz grain (right) (c) Source: ndsu.edu

While trying to model the catastrophic event, scientists at the University of California suggest that not one but two fireballs were created in the wake of the collision.  One - a hot fireball with temperatures of tens of thousands of degrees Celsius - was formed when the comet or asteroid and surface rocks vaporized.

This was followed in a few seconds by what the scientists are terming a warm fireball, created by the vaporization of underlying carbonate (carbonized plant remains).

This produced temperatures of only 1,000 C.

The models suggest that the second fireball would have disintegrated 2,000 cubic kilometres of material - 100,000 times more than went into constructing the Great Pyramid at Giza in Egypt.

It would also have ejected large amounts of carbon dioxide, lime, water vapour and sulphur into the atmosphere. Other scientists have recently speculated that the sulphur could have covered the planet in a fog that might have lasted for decades. Theoretically, this would have reduced the amount of sun reaching Earth by 20 per cent and lowered global average temperatures 10 to 15 degrees.

The new calculations did not reveal whether the fireballs remained apart or melded together in a phenomenon reminiscent of a spectacular fireworks display.