A Seismic Shift In Understanding How The Earth Got Its Gas

The researchers, led by Dr Chris Ballentine from the University of Manchester, concluded that meteorite bombardment, after the moon was first formed, was the only way gases could have arrived so deep within the Earth - craters on the moon attest to the ferocity of this process.

The research, funded by the Natural Environment Research Council, has profound implications for our understanding of Earth's early history.

Dr Ballentine said: "Before the moon formed the Earth had a massive atmosphere. Scientists have argued for decades that lava lakes underneath this atmosphere contained dissolved gases, in exactly the same way that carbon dioxide gas is pressurised into fizzy drinks.

"They believed currents in the magma oceans would take this dissolved gas deep into the Earth where the molten rock would eventually freeze, trapping the gases.

"But we know that a planet the size of Mars smashed into the Earth to form the moon. This devastating impact would have destroyed the early atmosphere and released any trapped gas, even from deep within the Earth," he explained.

"So we asked the question, `why do volcanoes still spew out gases from so deep, to this day?'"

The team sampled volcanic gases in New Mexico. Uniquely, volcanic gases here contain very little air contamination and this allowed the team to measure rare gas isotopes, like neon, for the first time. These isotopes can be used to 'fingerprint' the origin of the volcanic gas.

The team found that these fingerprints were identical to gases found trapped in meteorites and not from an early atmosphere. The only way that these gases could have been added to the deep Earth is by continued meteorite bombardment after the moon was formed.

According to Dr Ballentine, tectonic activity on a huge scale must have dragged the gases trapped in the meteorites from the surface downwards.

Dr Ballentine's work paves the way to acceptance of the theory that the whole mantle, the bit between the Earth's crust and its core, convects like a pot of water on the stove - albeit very slowly - removing heat from deep within the Earth.

The team concluded that the whole mantle convective movement drives continental plate motion, controls the rate at which continents grow, and determines the amount of water, carbon and nitrogen that goes into and comes out of the Earth.