Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Study reconciles long-standing contradiction of deep-earth dynamics

25.08.2005


New databases give researchers a look into processes inside the Earth’s mantle

Researchers at Columbia University’s Lamont-Doherty Earth Observatory recently resolved a long-standing contradiction about the workings of the deep Earth. For years, many geochemists have argued that parts of the deep mantle remain unchanged since the formation of the Earth, whereas many geophysicists and geodynamicists have held that the entire mantle has been convecting (moving and mixing) over geological time.

Based on a synthesis of data on global oceanic magmatism, Cornelia Class and Steven L. Goldstein show that the evidence actually favors whole-mantle convection, with the deepest parts of the Earth affected by the tectonic processes that occur at the surface. Their study will appear in the August 25 issue of the journal Nature.



"For thirty years scientists have been debating whether there is a layer in the mantle that has remained unchanged since the formation of the Earth," said Class, a Doherty Associate Research Scientist. "The new on-line databases made it possible for the first time to reevaluate the geochemical arguments based on a complete synthesis of global data on oceanic basalts. We found that the strongest evidence previously put forth in favor of a layered mantle actually indicates the opposite is true."

The question of whether the Earth’s interior operates on a "layered" or "whole-mantle" model is central to scientists’ understanding of how the Earth loses its internal heat. The main process of heat loss occurs through melting of the mantle to form magma. If the layered model is correct, then a large portion of the deep earth never melts and never reaches the surface. Evaluations of seismic waves generated by earthquakes indicate that continental and oceanic plates sink all the way to the core-mantle boundary, an observation that supports whole-mantle convection. However, evidence from trace amounts of helium in lavas have been interpreted as requiring that the mantle is composed of layers that are isolated from each other.

When magma is erupted by volcanoes, helium and other gasses from the mantle are expelled to the atmosphere. Unlike other gases, the helium is so light that it is lost forever to space. As a result, the Earth’s inventory of 3He, the light isotope of helium, is considered "primordial," dating from the time of the formation of the planet. Indications of a high proportion of primordial helium in ocean island lavas, like those found in Hawaii, have been taken as evidence for a layer in the deep mantle that has never been melted and, hence, never degassed.

"This result adds to growing evidence that most of Earth’s mantle has been subject to the same forces that drive the movements of Earth’s crust," said Sonia Esperanca, a Program Director in the National Science Foundation’s Division of Earth Sciences, which funded the research.

Class and Goldstein’s re-evaluation of this concept of the inner Earth was based on their work with two new databases that for the first time compile all of the published data on the geochemistry of oceanic volcanism around the world: the Petrological Database of Ocean Floor Basalts (PetDB, based at Lamont) and Geochemistry of Rocks from the Oceans and Continents (GEOROC).

It has long been known that the upper mantle sources of basalt found at mid-ocean ridges, formed by sea floor spreading, have been previously melted to form oceanic and continental crust. The new global data synthesis demonstrates that the ocean island lavas that are chemically most like mid-ocean ridge basalt also contain the highest primordial helium signal. As a result, this helium signal actually indicates previous processing by plate tectonics, rather than a primordial mantle source. Class and Goldstein conclude that helium must be degassed inefficiently to the atmosphere through volcanic processes and enough remains in the mantle during melting to give the false impression that the deep mantle is primordial.

"Our results mean we can dispense once and for all with the argument that the helium data require a primordial layer in the mantle, whose existence has been difficult to reconcile with the rest of what we know about how the Earth works," said Goldstein, a professor of Earth and Environmental Sciences at Columbia University and member of the Lamont-Doherty senior staff. "The implications of our work will be hotly debated, but I expect these new observations to change the way we view deep-Earth dynamics."

Ken Kostel | EurekAlert!
Further information:
http://www.columbia.edu
http://www.ldeo.columbia.edu
http://www.earth.columbia.edu

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 >>>