"They show for the first time that the water content completely goes down" during the lightning strike, leaving behind a clean surface in which environmental water can accumulate, says geochemist Matthew Pasek of the University of South Florida.
Next, the researchers tried to apply the dating system to natural fulgurites. They climbed volcanic peaks in Oregon to hammer out the shiny, black samples. The glassy rocks"stand out in stark relief" from the surrounding rocks, Castro says. Close inspection of the fulgurites' outer rinds revealed higher levels of moisture that decreased sharply further into the rock. These moisture profiles behaved very"mathematically," Castro says—good for dating. The scientists calibrated their clock by using computer models to figure out what rate of moisture absorption best accounted for the profiles seen in the samples.
They found that some of the fulgurites were hundreds of years old. More importantly, the method could. That offers sharper time resolution than that of techniques that rely on the bombardment of rocks by cosmic rays. In addition to shedding light on historic lightning patterns, the team believes the new method could reveal when mountaintops became vulnerable to lightning strikes.
For example, fulgurites could show when ice age glaciers began to retreat. Geologists already know where: Mountainous piles of debris, called terminal moraines, record the farthest thrust of an advancing glacier. In mountainous regions, these moraines should include fulgurites. By dating them, scientists can pin down the timing of the retreat, which could help reconstruct past climate trends, Castro says."They're going to be a very powerful way to bracket the ages of moraines.
Isn't that great, fosiled lightning bolts...