Discovery of 2 billion year old rocks may shed light on mantle formation

Washington, April 12 : Geologists have unearthed ancient rocks from the ocean floor of the North Pole that date back to 2 billion years, which may shed light on the formation of the mantle, the vast layer that lies beneath the planet's outer crust.

Led by Jonathan Snow, assistant professor of geosciences at University of Houston (UH), the team of geologists collected the mantle rock during an expedition to the North Pole aboard a 400-foot-long icebreaker, a research vessel designed to break through the ice.

These two-billion-year-old rocks were found along the bottom of the Arctic Ocean floor, unearthed during research voyages in 2001 and 2004 to the Gakkel Ridge, an approximately 1,000-mile-long underwater mountain range between Greenland and Siberia.

This massive underwater mountain range forms the border between the North American and Eurasian plates beneath the Arctic Ocean, where the two plates diverge.

The mantle, the rock layer that comprises about 70 percent of the Earth's mass, sits several miles below the planet's surface.

Mid-ocean ridges like Gakkel, where mantle rock is slowly pushing upward to form new volcanic crust as the tectonic plates slowly move apart, is one place geologists look for clues about the mantle.

Gakkel Ridge is unique because it features - at some locations - the least volcanic activity and most mantle exposure ever discovered on a mid-ocean ridge, allowing Snow and his colleagues to recover many mantle samples.

According to Snow, "We can't exaggerate how important these rocks are - they're a window into that deep part of the Earth."

Venturing out aboard the research icebreaker, Snow and his team sifted through thousands of pounds of rocks scooped up from the ocean floor by the ship's dredging device. The samples were labeled and cataloged and then cut into slices thinner than a human hair to be examined under a microscope.

That is when Snow realized he found something that, for many geologists, is as rare and fascinating as moon rocks - mantle rocks devoid of sea floor alteration.

Analysis of the isotopes of osmium, a noble metal rarer than platinum within the mantle rocks, indicated they were two billion years old.

The discovery of the rocks suggests the mantle is not as well-mixed or homogenous as geologists previously believed, revealing that the Earth's mantle preserves an older and more complex geologic history than previously thought.

This opens the possibility of exploring early events on Earth through the study of ancient rocks preserved within the Earth's mantle.

ANI