Sure, 2008 was bad. But for Americans it was nowhere near as bad as 11,000BC – according to research published in Science magazine yesterday.

At about that time, say scientists, a massive comet struck the atmosphere somewhere above North America, broke into pieces and rained down fire and death – wiping out the early Palaeo-Americans, also known as Clovis people, and making creatures such as the woolly mammoth, mastodon, short-faced bear, sabre-toothed cat, ground sloth and giant armadillo extinct. Not to forget the American camel and the American lion.

Although this theory first emerged a year ago and has been hotly debated ever since, the authors of the Science article present compelling evidence to support it – in the form of nanodiamonds.

These, which are so small they are barely visible even under the most advanced microscopes, have been found embedded in 13,000-year-old sediment in North America and Europe. The only plausible explanation for this, say the authors, is a planetary catastrophe of the sort that bade farewell to the dinosaurs about 65 million years earlier.

“There’s no other way we can interpret the presence of these diamonds other than an extraterrestrial impact,” said James Kennett, one of the authors and a palaeo-oceanographer at the University of California in Santa Barbara.

In some ways the theory seems almost too good to be true. Scientists have long been at a loss to explain the sudden and seemingly inexplicable disappearance of the Clovis people and megafauna (large animals) at the end of the last Ice Age – even though many of the species survived previous Ice Ages. The equally sudden 1,300-year mini Ice Age that followed, known as the Younger Dryas, has also been an unsolved conundrum.

Before the comet theory it was assumed that the Clovis hunted the megafauna to extinction and were then killed by the rapidly falling temperatures.

The comet theory might even explain the Younger Dryas, say the authors. They argue that the impact might have melted part of the Laurentide glacier in Canada, causing a Mississippi tsunami, which burst into the Gulf of Mexico and redirected the warmer currents of the Atlantic.

Scientists have long suspected that the Younger Dryas was caused by ocean currents being shut down but they had no realistic theory for why that might have happened. If such an extraterrestrial calamity occurred, sceptics argue, there would be evidence of a crater or deformed rock debris. Proponents of the theory, however, say that a comet, which might have been up to 5km (3 miles) wide, could have broken up before plunging to Earth.

Yet sceptics counter that this would not create shockwaves powerful enough to create diamonds. Some are unconvinced that what the researchers found are nanodiamonds, even though they were confirmed by three laboratories. Undeterred, the authors point to other evidence. In the sediment they analysed is an unmistakeable black layer of soot and charred foliage, along with iridium and carbon spheres, in which the nanodiamonds are encased. This is typical of an extraterrestrial impact. The position of the diamond layer is the same at other sites across the world, indicating that they were formed by the same event. The wide distribution of the diamonds supports the idea that the comet broke into pieces. as it fell to earth.

Blasts from past

— The meteorite that may have killed the dinosaurs was said to have hit the Earth 65 million years ago. Other theories include the possibility that they were extinguished by a plague of insects

— The largest meteorite strike in Britain is thought to have taken place 1.2 billion years ago in what is now the Scottish town of Ullapool. It scattered material over 31 miles

— Experts believe that the Tunguska event, a blast in the Siberian wilderness in 1908 that was 1,000 times more powerful than the Hiroshima bomb, was caused by a comet or asteroid

— A meteorite big enough to have wiped London off the map hit Siberia in 2003. Its destruction extended for more than 40 miles

— In 2007 a meteorite said to have landed in the town of Carancas, Peru, brought with it a strange odour and mysterious illness that affected 200 people

Source: Times archives

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