Einstein Science Reporting for Kids
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American Association for the Advancement of Science

When did 'pet rocks' and 'wild rocks' become cool?

"Pet rocks" became cool in 1975 -- they suddenly seemed like the perfect low-maintenance pet, and almost instantly, people were buying pet rocks like crazy. You could teach a pet rock to sit and play dead instantly!

"Wild Rocks" from a mountain valley in the Coast Mountains of British Columbia, Canada became cool about 1.8 million years before pet rocks became cool, according to new research that provides a history of when the mountain valley formed. Instead of becoming cool in the popularity sort of way like pet rocks, the "wild rocks" from the mountain valley in Canada became cool -- or at least cooler -- in the temperature kind of way.

Exactly when these "wild rocks" cooled down tells the scientists when the rocks moved closer to the surface of the Earth. Knowing when the rocks moved closer to the surface of the earth helps to explain when the valley formed as rocks even closer to Earth's surface wore away through the process of "erosion."

For a long time, scientists have wondered if the wearing away of rocks in mountain valleys is mostly due to the work of rivers or due to moving sheets of ice called alpine glaciers.

In this particular valley, and perhaps in other valleys, the new research suggests that the action of moving glaciers is responsible for much of the erosion of rocks that helped to form the valley.

To figure out when the valley rocks got cool, the researchers used a new technique that measures the location of a particular "flavor" of the element helium in tiny grains of a mineral called apatite. This process of measuring the history of rock cooling is called "thermochronometry," according to Science author David Shuster who works at Berkeley Geochronology Center in Berkeley, California.

Measuring the history of rock cooling in other places in the world could provide more insights into when and why other mountain valleys formed.

This research appears in the 09 December 2005 issue of the journal Science.