A DEVASTATING collision between the Earth and a wayward

comet which wiped out nearly every living thing across an

entire continent will happen again and cost millions of lives,

a Westcountry scientist claims.

The three-mile wide comet, named Clovis after the fledgling

North American civilisation it drove to extinction, exploded in

the atmosphere 13,000 years ago with a force of 20 million

megatons – larger than a simultaneous blast by all the nuclear

weapons in history, says Professor Chris Turney, of the

University of Exeter.

It left no impact crater but sparked the biggest wildfires

in history, which stretched across the continent and suffocated

humans and animals with overwhelming amounts of soot and smoke,

leaving the few survivors with no vegetation or prey to live

on.

Fiery debris from the comet also melted huge portions of the

ice sheet, which drastically altered the planet's climate.

Massive volumes of fresh water found their way into the oceans

and changed their currents, plunging the Earth into an Ice Age

for 1,000 years.

Although NASA is tracking up to 5,000 comets and asteroids

throughout the Solar System, of which 700 are over a mile wide,

scientists say the vastness of space means many inevitably have

not been detected, and only one has to be on a collision course

with Earth to cause unprecedented carnage.

The theory is the subject of a new TV documentary on the

History Channel at 8pm tonight.

Speaking on the programme, Prof Turney, professor of

physical geography at the University of Exeter, said another

large comet would cause unimaginable damage.

He said: "We're just starting to work out for a fact that

comets are far more frequent than we were led to believe.

"If it just exploded as an air burst, it would fry a city

and basically just destroy it. There would not really be much

left at all, apart from a bit of rubble.

"It would be the end of the world scenario for those

people."

Experts believe the aftermath of such an impact would

accelerate global warming and cause the destruction of large

areas of coastline around the world as sea levels rose.

Prof Turney said the Clovis explosion caused the largest

forest fires ever seen.

"It would have been a very strange place with charcoal and

dust everywhere on the surface where these fires had gone

through," he said.

Prof Turney said it was only pure chance the famous Tunguska

Event, a meteorite which exploded above Siberia exactly 100

years ago, destroyed a remote area of forest instead of heavily

populated cities like London, Paris or New York.

"Had it entered the atmosphere a few hours earlier, it would

have hit Western Europe, potentially costing millions of

lives," he said.

"If the comet of Tunguska had actually exploded over London,

it would have caused widespread devastation.

"We were just incredibly fortunate that this thing exploded

over Siberia. It was a total fluke."

The Tunguska meteorite was just 165ft in diameter, compared

with the three-mile wide Clovis comet.

Clovis archaeological sites across North America show a

two-inch "carbon mat" in the rock dating back 13,000 years,

indicating huge amounts of soot in the atmosphere, as well as

elements like iridium, which is brought to Earth from

space.

At the time, much of the continent was covered by forests

and vast grasslands, enabling wildfires to spread

uncontrollably.

Huge shockwaves from the explosion started hurricane-force

winds which fanned the flames at incredible speeds across the

land.

As the soot fell onto the ice sheet, the darker material

absorbed more sunlight which melted the ice and forced fresh

water into the oceans, sending global temperatures plunging by

5C to 10C.

Prehistoric Megastorms: Comet Storm is on the History

Channel at 8pm tonight.