Ancient Earth crust stored in deep mantle

Apr 24, 2013
Earth

Scientists have long believed that lava erupted from certain oceanic volcanoes contains materials from the early Earth's crust. But decisive evidence for this phenomenon has proven elusive. New research from a team including Carnegie's Erik Hauri demonstrates that oceanic volcanic rocks contain samples of recycled crust dating back to the Archean era 2.5 billion years ago. Their work is published in Nature.

Oceanic crust sinks into the Earth's mantle at so-called subduction zones, where two plates come together. Much of what happens to the crust during this journey is unknown. Model-dependent studies for how long subducted material can exist in the mantle are uncertain and evidence of very old crust returning to Earth's surface via upwellings of magma has not been found until now.

The research team studied from the island of Mangaia in Polynesia's Cook Islands that contain iron sulfide inclusions within crystals. In-depth analysis of the of these samples yielded interesting results.

The research focused on isotopes of the element sulfur. (Isotopes are atoms of the same element with different numbers of neutrons.) The measurements, conducted by graduate student Rita Cabral, looked at three of the four naturally occurring isotopes of sulfur—isotopic masses 32, 33, and 34. The sulfur-33 isotopes showed evidence of a with that stopped occurring in Earth's atmosphere about 2.45 billion years ago. It stopped after the Great Oxidation Event, a point in time when the Earth's skyrocketed as a consequence of oxygen-producing photosynthetic microbes. 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.

This indicates that the sulfur comes from a deep mantle reservoir containing crustal material subducted before the Great Oxidation Event and preserved for over half the age of the Earth.

"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," Hauri said.

Explore further: Mexico's Volcano of Fire blows huge ash cloud

More information: Research paper: dx.doi.org/10.1038/nature12020

Related Stories

Studying ancient Earth's geochemistry

Jan 18, 2013

Researchers still have much to learn about the volcanism that shaped our planet's early history. New evidence from a team led by Carnegie's Frances Jenner demonstrates that some of the tectonic processes driving volcanic ...

Volcanoes deliver two flavors of water

Feb 26, 2012

Seawater circulation pumps hydrogen and boron into the oceanic plates that make up the seafloor, and some of this seawater remains trapped as the plates descend into the mantle at areas called subduction zones. ...

Diamonds show depth extent of Earth's carbon cycle

Sep 15, 2011

Scientists have speculated for some time that the Earth's carbon cycle extends deep into the planet's interior, but until now there has been no direct evidence. The mantle–Earth's thickest layer –is ...

Deep recycling in the Earth faster than thought

Aug 10, 2011

The recycling of the Earth's crust in volcanoes happens much faster than scientists have previously assumed. Rock of the oceanic crust, which sinks deep into the earth due to the movement of tectonic plates, ...

Recommended for you

Erosion may trigger earthquakes

Nov 21, 2014

Researchers from laboratories at Géosciences Rennes (CNRS/Université de Rennes 1), Géosciences Montpellier (CNRS/Université de Montpellier 2) and Institut de Physique du Globe de Paris (CNRS/IPGP/Université Paris Diderot), ...

Strong undersea earthquake hits eastern Indonesia

Nov 21, 2014

A strong undersea earthquake hit off the coast of eastern Indonesia on Friday, but there were no immediate reports of injuries or serious damage and officials said it was unlikely to trigger a tsunami.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.