Once or twice a year a strange, heavy "nugget" from outer space, as small as a blood cell but weighing about a tonne, may zoom through the Earth at up to 1,500,000 kmh.

American scientists believe two earthquakes in 1993 were caused by these "strangelets" - an exotic form of matter that has not been directly detected yet.

They say that in October, 1993, a strangelet entered the planet near Antarctica in a violent explosion and exited south of India 27 seconds later. A month later, another hit the Pacific Ocean and left via Antarctica 19 seconds later. Shock waves were recorded in Australia and Bolivia.

The culprits are apparantly "strange quark nuggets"--exotic bits of matter hypothesized to drift through space, but never detected. First proposed by Witten in 1984. Other physicists have calculated that they would dash through Earth with dramatic effect: a 1-ton fleck would unleash the energy of a 50-kiloton nuclear bomb, spread along its entire threadlike path.

The scientists looked at hundreds of thousands of unexplained seismic events and found a few that could possibly be caused by such a hypothetical happening. (Or by chance!)

Geologist Eugene Herrin, of the Southern Methodist University in Texas says "There would probably be a tiny crater but it would be virtually impossible to find anything."

Australian physicist Anthony Thomas says "I don't think our knowledge of the structure of matter is good enough to know whether they (strangelets) do or don't exist."

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