Well water of the tiny Canadian town of Gypsumville, Manitoba (population 65) has been poisoned by an extraterrestrial.
The invader: A meteorite which struck down almost a quarter-billion years ago, creating the 25-mile-wide (40-kilometer) Lake Martin impact crater.
The ancient impact shattered the granitic ground so that extraordinary amounts of fluoride now taint the well water. Slightly higher than recommended amounts of fluoride can cause mottled teeth, while even higher concentrations can lead to neurological problems and softened bones.
This is could be the first time a meteor impact has been tied to a modern health threat, say the geologists who made the discovery.
Spotting the likely cause of the fluoride problem was simply a matter of overlaying a map of the well water fluoride concentrations with one that shows the geology of the area, said geochemist Matthew Leybourne of the New Zealand government’s Geological and Nuclear Sciences, Limited. Leybourne and his colleagues at the Canadian Geological Survey published their discovery in the February issue of the journal Geology.
“It was recognized in the past as having some problems with fluoride,” said Leybourne.
Correlating the fluoride with the impact structure pointed to a possible cause of the problem. The next step was to work out exactly how an impact so long ago could cause groundwater to have more fluoride today.
“If you look worldwide, high fluoride occurs in a lot of areas,” Leybourne told Discovery News.
In those instances two things are required: Granitic rocks containing the mineral fluorite and some way to make the fluorite more available to water. Normally hydrothermal activity plays a role, he said. But in Gypsumville, the mechanism is the meteor-shattered granite, which makes more of the fluorite mineral surfaces exposed to the groundwater.
“The impact changed the grain size,” said Leybourne.
It’s basically the same difference as having a few large blocks of salt in water compared to pulverized salt in water — which dissolves far more readily and makes the water far saltier.
Some other similar effects have been seen at other impact sites around the world, said Richard Grieve, Chief Scientist of Natural Resources Canada’s Earth Sciences Sector, which includes the Canadian Geological Survey. Grieve is an expert on impact geology but not a co-author on the Geology paper.
“They are a huge agent for change,” Grieve told Discovery News, regarding how meteor impacts affect local geology.
Impact craters elsewhere have previously been blamed for tinkering with the flows of water or hydrocarbons.
A good example, Grieve says, is the gigantic Chicxulub Crater, which intersects part of the Yucatan Peninsula in Mexico. The geological structures created by that 65-million-year-old impact channel water away from the city of Merida, home to almost a million people.
“That’s bad news for the people who live in the crater,” said Grieve. “They have a water problem.”
But now that they understand the geological cause of the problem, they can work out a solution, he said. And since the 175 known impact structures on Earth all overwhelm the local geology in similar ways, what applies at one crater can often apply to others.