This is where the case of the L'Aquila toads was different. Rachel Grant, a biologist from the Open University, was monitoring the toad colony as part of her PhD project. "It was very dramatic," she recalled. "It went from 96 toads to almost zero over three days."
Ms Grant published her observations in the Journal of Zoology. "After that, I was contacted by Nasa," she told BBC Nature.
Scientists at the US space agency had been studying the chemical changes that occur when rocks are under extreme stress. They wondered if these changes were linked to the mass exodus of the toads.
Their laboratory-based tests have now revealed, not only that these changes could be connected, but that the Earth's crust could directly affect the chemistry of the pond that the toads were living and breeding in at the time.
Nasa geophysicist Friedemann Freund showed that, when rocks were under very high levels of stress - for example by the "gargantuan tectonic forces" just before an earthquake, they release charged particles.
These charged particles can flow out into the surrounding rocks, explained Dr Freund. And when they arrive at the Earth's surface they react with the air - converting air molecules into charged particles known as ions.
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