Nav: Home

There and back again: Mantle xenon has a story to tell

August 08, 2018

The Earth has been through a lot of changes in its 4.5 billion year history, including a shift to start incorporating and retaining volatile compounds from the atmosphere in the mantle before spewing them out again through volcanic eruptions.

This transport could not have begun much before 2.5 billion years ago, according to new research by Washington University in St. Louis, published in the August 9 issue of the journal Nature.

"Life on Earth cares about changes in the volatile budget of the surface," said Rita Parai, assistant professor of geochemistry in Earth and Planetary Sciences in Arts & Sciences and first author of the study. "And there's an interplay between what the deep Earth was doing and how the surface environment changed over billion-year timescales."

Volatiles -- such as water, carbon dioxide and the noble gases -- come out of the mantle through volcanism and may be injected into the Earth's interior from the atmosphere, a pair of processes called mantle degassing and regassing. The exchange controls the habitability of the planet, as it determines the surface availability of compounds that are critical to life -- such as carbon, nitrogen and water.

The new model presented by Parai and collaborator Sujoy Mukhopadhyay, of the University of California, Davis, also establishes a range of dates during which the Earth shifted from a net degassing regime -- again, think about those oozy volcanoes -- to one that tilted the balance to net regassing potentially enabled by subduction, the conveyor-belt action of tectonic plates.

Mechanical properties change as water is added or removed from the mantle, so the onset of regassing had an important effect on the internal churning of the mantle, known as convection, which controls plate motions at the surface, Parai said.

Parai uses noble gases to address questions about how planetary bodies form and evolve over time. In this new research, she modeled the fate and transport of volatile compounds into the Earth's mantle using xenon isotopes as tracers.

"Xenon is an excellent volatile tracer, because all minerals that carry water also carry xenon," Parai said. "So if xenon regassing was negligible, water regassing must also have been negligible during the Archean (4 billion-2.5 billion years ago)."

Substantial regassing began sometime between a few hundred million to 2.5 billion years ago, the researchers found.

If plate tectonics and subduction began earlier than 2.5 billion years ago, then perhaps by then the Earth's interior had cooled sufficiently for volatiles to remain in subducting plates, rather than getting released and percolating back to the surface through magmatism, Parai suggests.

"Most people rarely have an occasion to think about volatiles trapped in the Earth's interior," Parai said. "They're present at low concentrations, but the mantle is huge in terms of mass. So for the Earth's total volatile budget, the mantle is an important reservoir."

She plans to focus her future research on pushing the limits of precision in xenon isotopic measurements in a variety of geological samples.

"The more observational constraints we have, the better," she said.
-end-


Washington University in St. Louis

Related Plate Tectonics Articles:

The birth and death of a tectonic plate
Geophysicist Zachary Eilon developed a new technique to investigate the underwater volcanoes that produce Earth's tectonic plates
Experts explain origins of topographic relief on Earth, Mars and Titan
The surfaces of Earth, Mars, and Titan, Saturn's largest moon, have all been scoured by rivers.
Scientists describe origins of topographic relief on Titan
Fluid erosion has carved river networks in at least three bodies in our solar system in the form of water on Earth and Mars and liquid hydrocarbons on Titan.
Southern Italy: Earthquake hazard due to active plate boundary
Tectonically, the Mediterranean is extremely active and thus threatened by natural catastrophes.
Release of water shakes Pacific Plate at depth
A team of seismologists analyzing the data from 671 earthquakes that occurred between 30 and 280 miles beneath the Earth's surface in the Pacific Plate as it descended into the Tonga Trench were surprised to find a zone of intense earthquake activity in the downgoing slab.
SLU geologists discover how a tectonic plate sank
Saint Louis University researchers report new information about conditions that can cause the Earth's tectonic plates to sink into the Earth.
The evolution of antibiotic resistance, on a plate
Researchers have developed a large culturing device to track the evolution of bacteria as they mutate in the presence of antibiotics, revealing that, surprisingly, the fittest mutants were not those most likely to infiltrate higher antibiotic concentrations.
Crystallization plate provides clues on protein structure aboard historic space mission
A new crystallization plate, developed and tested at the Cornell High Energy Synchrotron Source, or CHESS, hitched a ride to outer space and is helping a major drugmaker learn about protein structure.
New insights on the relationship between erosion and tectonics in the Himalayas
Can processes unfolding at the Earth's surface be strong enough to influence tectonics?
Earth's mantle appears to have a driving role in plate tectonics
Deep down below us is a tug of war moving at less than the speed of growing fingernails.

Related Plate Tectonics Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Jumpstarting Creativity
Our greatest breakthroughs and triumphs have one thing in common: creativity. But how do you ignite it? And how do you rekindle it? This hour, TED speakers explore ideas on jumpstarting creativity. Guests include economist Tim Harford, producer Helen Marriage, artificial intelligence researcher Steve Engels, and behavioral scientist Marily Oppezzo.
Now Playing: Science for the People

#524 The Human Network
What does a network of humans look like and how does it work? How does information spread? How do decisions and opinions spread? What gets distorted as it moves through the network and why? This week we dig into the ins and outs of human networks with Matthew Jackson, Professor of Economics at Stanford University and author of the book "The Human Network: How Your Social Position Determines Your Power, Beliefs, and Behaviours".