Earth's evolution 'all about gas'

Earth's evolution 'all about gas'

It has long been argued about how the Earth evolved from a primitive state in which it was covered by ocean of molten rock into the planet we live on today with a solid crust made of moving tectonic plates, oceans and an atmosphere.

Now, an international team, led by Dr Mark Kendrick at the University of Melbourne, has shown that atmospheric gases are mixed into the mantle, inside the Earth's interior, during the process called "subduction" when tectonic plates collide and submerge beneath volcanoes in subduction zones.

"This finding is important because it was previously believed that inert gases inside the Earth had primordial origins and were trapped during the formation of the solar system," Dr Kendrick said.

Because the composition of neon in the Earth's mantle is very similar to that in meteorites, it was recently suggested by scientists that most of the Earth's gases were delivered by meteorites during a late meteorite bombardment that also generated visible craters on the Earth's moon.

"Our study suggests a more complex history in which gases were also dissolved into the Earth while it was still covered by a molten layer, during the birth of solar system," he said. It was previously assumed that gases could not sink with plates in tectonic subduction zones but escaped during eruption of overlying volcanoes. "The new study shows this is not entirely true and the gases released from Earth's interior have not faithfully preserved the fingerprint of solar system formation," Dr Kendrick said.
For their research, the scientists collected serpentinite rocks from mountain belts in Italy and Spain. These rocks originally formed on the seafloor and were partially subducted into the Earth's interior before they were uplifted into their present positions by collision of European and African plates.

By analysing the inert gases and halogens trapped in these rocks, the team was able to show gases are incompletely removed by the mineral transformations affecting serpentinites during the subduction process and hence providing new insights into the role of the trapped gases in Earth's evolution.

The findings have been published in the latest edition of the 'Nature Geoscience' journal.