Volcanoes' meteorite past
Gas deposited by meteorites cause volcanoes to erupt
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Wednesday, 10, Sep 2008 12:01
Violent volcanic eruptions witnessed from the dawn of time to the present day could all have been prompted by meteorite strikes billions of years ago.
Geologists are presenting new evidence that contradicts the belief the gas that causes volcanoes to erupt - 'light' helium - came to Earth via its gravitational pull.
Volcanic eruptions occur when the gas, which arrived when the world was in a molten state and is trapped in the deep Earth, melts.
But University of Manchester scientists say that the 'fingerprint' left by the 3He isotope does not match solar nebula but instead meteorites.
"We have shown that the neon gas fingerprint expected for the captured solar nebula model is not matched," Professor Chris Ballentine said.
"Instead we have found a meteorite signature, which suggests the massive early atmosphere is not trapped by gravitational attraction as originally thought but a result of meteorites spewing out gas on impact."
Prof Ballentine and his team also identified a second signature, obtained via studying CO2 gas from the Colorado Plateau, which is identical to seawater.
"The only explanation for this is that seawater trapped in ocean crust is being driven back down into the deep Earth in a tectonic process called subduction," he explained.
Previous thinking had stated that water at these depths would be impossible due to it melting during the subduction process.
"This process has the potential to fundamentally change how scientists think Earth has behaved over time. Even a little bit of water added to rock in the deep earth makes it more plastic and allows movement of tectonic plates sitting on top to be quicker," Prof Ballentine added.
"The source and fate of atmospheres and water on planets is central to understanding the origin of life and the conditions that lead to our own planet looking as it does today. Our work provides evidence that changes our big picture understanding of how planetary systems acquire their volatile elements."