Ocean Volcanoes Spew Out Material From Eons Ago, Study Says

Using samples of volcanic rock taken from the ocean, scientists have further solidified the theory that the lava that erupts from certain volcanoes contains ancient materials from the Earth's early crust.

Erik Hauri, from the Carnegie Institute for Science, and his team demonstrated that oceanic volcanic rocks contain samples of recycled crust dating back to the Archean era 2.5 billion years ago, according to a statement from the Carnegie Institute.

Much of what happens to the Earth's crust when the tectonic plates merge together at the subduction zones is unknown, and model-dependent studies have long been uncertain of how long subducted material can exist in the mantel. Evidence of very old crust returning to Earth's surface has not been found until now.

The team analyzed volcanic rock samples from Mangaia in Polynesia's Cook Islands.

The research team analyzed sulfur isotopes in the ocean rocks and found evidence of a chemical interaction with UV radiation that stopped occurring on Earth some 2.45 billion years ago, after an event called the Great Oxidation, which saw the oxygen levels on the planet skyrocket as a consequence of oxygen-producing microbes. According to the statement, prior to the Great Oxidation Event, the atmosphere lacked ozone. But once ozone was introduced, it started to absorb UV and shut down the process.

"These measurements place the first firm age estimates of recycled material in oceanic hotspots," Hauri said. "They confirm the cycling of sulfur from the atmosphere and oceans into mantle and ultimately back to the surface."

The find indicates that the rocks contain material that comes from deep within the Earth from before the Great Oxidation and have been preserved for eons

The work is published in Nature.