Swells up to a mile high swept the planet, drowning everything.

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Scientists scoured thousands of miles of seabed for evidence of disturbed and eroded sediments.

And they came up with their theory based on what they found at more than 100 sites worldwide and computer simulations.

An eight-mile wide asteroid hit the Gulf of Mexico at 27,000mph 66 million years ago.

Its initial energy was up to 30,000 times greater than the Boxing Day 2004 tsunami, which killed more than 230,000.

Molly Range, of the University of Michigan, US, said: “This tsunami was strong enough to disturb and erode sediments in ocean basins halfway around the globe, leaving either a gap in the sedimentary records or a jumble of older sediments.

“Depending on the geometries of the coast and the advancing waves, most coastal regions would be inundated and eroded to some extent.

“Any historically documented tsunamis pale in comparison with such global impact.”