A space rock that smashed into Canada more than 200 million years ago is being blamed for health risks faced today by several communities in central Manitoba, according to a new international study of groundwater quality around the ancient Lake St. Martin meteorite crater north of Winnipeg.

In what's being described as the first-ever finding of a modern-day health threat posed by a prehistoric meteorite strike, the researchers say elevated levels of fluoride and other chemicals in the area's groundwater can be traced to the shattering of subsurface granite when the extraterrestrial object slammed into Earth nearly a quarter of a billion years ago.

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An aerial view of Lake St. Martin, Manitoba.


"The possibility that a meteor impact could devastate modern human civilization is a real concern," especially given such events as the dinosaur-killing strike on the Yucatan Peninsula 65 million years ago, the researchers note in their study of the Lake St. Martin crater in central Manitoba, published in the February issue of Geology.

"However, meteors may affect human populations through more subtle routes in addition to these commonly recognized, catastrophic events."

Located between Lake Manitoba and Lake Winnipeg about 250 north of Winnipeg, Lake St. Martin is believed to be the site of a meteorite strike about 230 million years ago that left a 24-kilometre-wide crater, now largely obscured by time.

Scientists recently theorized that the Manitoba site has sister craters in France, Quebec, North Dakota and Russia - all created within hours of each other when large pieces of a fragmented meteor struck Earth.

For years, Canadian scientists have been trying to understand the cause of poor water quality in the town of Gypsumville and two nearby First Nations communities around Lake St. Martin. High levels of fluoride, well beyond recommended health limits, have forced area residents to seek alternative water supplies.

The new study - led by New Zealand-based geoscientist Matt Leybourne and two of his former colleagues at the Geological Survey of Canada - shows how shocked, fractured and melted rocks around the ancient impact site allow fluoride to leach more easily into the area's groundwater. Nearby rocks beyond the crater don't show the same leaching effect.

"It's a smoking gun that's been smoking for a long time," Ottawa-based scientist Jan Peter, co-author of the study, told Canwest News Service. "We don't know of anybody else who's made that kind of a link."

Elevated fluoride is "a major health issue in many parts of the world" that can cause damage to teeth, softening of bones, calcified tendons and ligaments and neurological damage, the study states.

Peter said the communities around Lake St. Martin have long been aware of the groundwater contamination, but now have a clearer explanation - reaching back to the Triassic age - of when the problem began.

He added: "The best guesstimate is that the meteorite strike was around 230 million years ago. That's a heck of a long time to still be having its impact felt."