In the Earth’s atmosphere, lighting is continuously zapping: about 45 times per second, by one estimate, with most of those strikes occurring over land.

Now, scientists in Florida are using a novel method to analyze the energy from some lightning strikes—  by analyzing the “fossils” they leave behind in sand.

After lightning hits sand, sometimes it creates a glass tube that researchers call a fulgurite. Scientists have collected 266 of these remnants from lightning strikes captured in two sand mines in Polk County, Florida, and the length and circumference of the fulgurites can tell them just how much energy the lightning was packing. They believe that the site they studied contains the remnants of strikes that have taken place over thousands of years.

“The structure of the fulgurite, created by the energy and heat in a lightning strike, can tell us a lot about the nature of the strike, particularly about the amount of energy in a single bolt of lightning,” Matthew Pasek, an associate professor at the University of South Florida School of Geosciences, and the first author on a new study on the topic, said in a statement.

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“Everyone knows there is a lot of energy in a lightning bolt, but how much?” he said.  “Ours is the first attempt at determining lightning energy distribution from fulgurites and is also the first data set to measure lightning’s energy delivery and its potential damage to a solid earth surface.”

Their method means that they can estimate how powerful a strike was that took place even in the distant past. Lightning is so hot that it heats the air to over 53,000 degrees, according to Pasek, who estimates that as many as 10 fulgurites may be formed every second around the world from lightning.

Their research was published in the journal Scientific Reports.

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