Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Earth could hold more water

08.03.2002


A more watery lower mantle would churn faster.
© SPL


Five times as much water as in all the world’s oceans may lurk deep below its surface.

Geologists have divined water where you might least expect it: 1,000 kilometres below the Earth’s surface. Here, rocks heated to over 1,000 oC and squeezed under high pressures may harbour around five times as much water as in all the world’s oceans. This could give clues to how the Earth formed and how it behaves today.

Between 650 and 2,900 km below the Earth’s surface hot, compressed minerals surround the planet’s iron-rich core. Called the lower mantle, this material may hold up to 0.2 per cent of its own weight in water, estimate Motohiko Murakami, of the Tokyo Institute of Technology in Japan, and colleagues1.



Theories of planetary formation take into account how much easily vaporized material, such as water and carbon dioxide, were originally present. The findings hint that Earth’s starter mix may have been sloppier than anticipated.

Water would lower the melting point of rocks in the lower mantle and increase their viscosity. Over millions of years, the mantle churns like a pan of hot soup. This moves the tectonic plates and mixes the mantle’s chemical components. A more viscous mantle would churn faster.

The take-up of water by minerals in the lower mantle might also affect the ease with which tectonic plates sink deep into the Earth. As the plates descend, heat up and become squeezed, the water that they release might soften the surrounding mantle and ease their passage.

There is already thought to be several oceans’ worth of water slightly higher in the mantle, at a depth of around 400-650 km. This region is called the transition zone, as it is between the upper and the lower mantle.

The lower mantle’s minerals can retain about a tenth as much water as the rocks above, Murakami’s team finds. But because the volume of the lower mantle is much greater than that of the transition zone, it could hold a comparable amount of water.

"The findings will boost the debate about how much water is locked away in the mantle," says geologist Bernard Wood of the University of Bristol, UK. Until now, he says, "most people would have argued that there isn’t much water in the mantle". A similar study two years ago concluded that there isn’t much water down there at all2.

Taking on the mantle

Murakami’s team mimicked the lower mantle in the laboratory. They studied the three kinds of mineral thought to make up most of the region: two perovskites, one rich in magnesium, the other in calcium, and magnesiowustite, a mixture of magnesium and iron oxides.

To recreate the its furious conditions, the researchers used a multi-anvil cell. This heats materials while squeezing them between hard teeth. Having baked the minerals at around 1,600 oC and 250,000 atmospheres, the team measured how much hydrogen the rocks contained using secondary-ion mass spectrometry. This technique blasts the material with a beam of ions and detects the ions sprayed out from the surface.

Any hydrogen in the rocks presumably comes from trapped water, an idea that other measurements support. The researchers found more hydrogen than previous experiments had led them to expect.

References

  1. Murakami, M., Hirose, K., Yurimoto, H., Nakashima, S. & Takafuji, N. Water in Earth’s lower mantle. Science, 295, 1885 - 1887, (2002).
  2. Bolfan-Casanova, N., Kepler, H. & Rubie, D.C. Water partitioning between nominally anhydrous minerals in the MgO-SiO2-H2O system up to 24 GPa: implications for the distribution of water in the Earth’s mantle. Earth and Planetary Science Letters, 182, 209, (2000).


PHILIP BALL | © Nature News Service

More articles from Earth Sciences:

nachricht Massive impact crater from a kilometer-wide iron meteorite discovered in Greenland
15.11.2018 | Faculty of Science - University of Copenhagen

nachricht The unintended consequences of dams and reservoirs
14.11.2018 | Uppsala University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: UNH scientists help provide first-ever views of elusive energy explosion

Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.

Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...

Im Focus: A Chip with Blood Vessels

Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.

Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

Im Focus: Research icebreaker Polarstern begins the Antarctic season

What does it look like below the ice shelf of the calved massive iceberg A68?

On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.

Im Focus: Penn engineers develop ultrathin, ultralight 'nanocardboard'

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure

Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

European Space Talks: Weltraumschrott – eine Gefahr für die Gesellschaft?

23.10.2018 | Event News

 
Latest News

Purdue cancer identity technology makes it easier to find a tumor's 'address'

16.11.2018 | Health and Medicine

Good preparation is half the digestion

16.11.2018 | Life Sciences

Microscope measures muscle weakness

16.11.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>