New study suggests Earth's lower mantle penetrated by metallic blobs

Dec 13, 2012 by Bob Yirka report
New study suggests Earth’s lower mantel penetrated by metallic blobs
Distribution of Mg and Fe in the annealed couples of molten Fe and solid (Mg,Fe)O. Credit: (c) Nature 492, 243–246 doi:10.1038/nature11663

(Phys.org)—Researchers from Yale University have found that molten iron is able to penetrate into rock samples in a unique way under certain conditions. Geophysicist Shun-ichiro Karato and student Kazuhiko Otsuka together have found that when molten iron is brought into contact with magnesium-iron oxide crystals under high pressures and temperatures, metal blobs form inside the crystals – suggesting that it might be possible that the Earth's lower mantle might consist of a similar metal heavy material. They present their findings in a joint paper published in the journal Nature.

The Earth, as most science students know, has three main parts: the crust, the mantle and the core. Scientists learn more about the makeup of the mantle and core by studying seismic waves sent through them, and studying the way change as the pass through the different layers. Studies done over the years have led researchers to believe that the lower part of the mantle has been imbued with iron from the core. But, other research has shown that simple diffusion would not be sufficient to account for the amount of metal that appears to exist there, nor would other known processes. In this new research, the team suggests it got there by a means never before seen.

The researchers created a , heated environment where they caused samples of molten iron to come into contact with crystals of magnesium-. After just a few minutes they noted that iron rich blobs of liquid began penetrating into the crystals. In their lab the penetration was just 100 micrometers, but the two suggest that in a much larger environment, such as where the Earth's core meets the mantle, such penetration could extend to 100 kilometers, offering an explanation of why the lower mantle appears to have so much iron in it. They suggest that the blobs form due to an instability that occurs in the concentration gradient of iron oxide in the crystal.

This new research may also help to explain what appear to be dense layers observed in other planets as well. But, because magnesium-iron oxide is rather rare in the Earth's mantle, new research will focus on finding other minerals that behave in the same way when exposed to molten iron.

Explore further: Climate impacts of changing aerosol emissions since 1996

More information: Deep penetration of molten iron into the mantle caused by a morphological instability, Nature 492, 243–246 (13 December 2012) doi:10.1038/nature11663

Abstract
The core–mantle boundary of Earth is a region where iron-rich liquids interact with oxides and silicates in the mantle. Iron enrichment may occur at the bottom of the mantle, leading to low seismic-wave velocities and high electrical conductivity, but plausible physical processes of iron enrichment have not been suggested. Diffusion-controlled iron enrichment is inefficient because it is too slow6, although the diffusion can be fast enough along grain boundaries for some elements. More fundamentally, experimental studies and geophysical observations show that the core is under-saturated with oxygen, implying that the mantle next to the core should be depleted in FeO. Here we show that (Mg,Fe)O in contact with iron-rich liquids leads to a morphological instability, causing blobs of iron-rich liquid to penetrate the oxide. This morphological instability is generated by the chemical potential gradient between two materials when they are not in bulk chemical equilibrium, and should be a common process in Earth's interior. Iron-rich melt could be transported 50 to 100 kilometres away from the core–mantle boundary by this mechanism, providing an explanation for the iron-rich regions in the mantle.

Related Stories

A new kind of metal in the deep Earth

Dec 19, 2011

(PhysOrg.com) -- The crushing pressures and intense temperatures in Earth's deep interior squeeze atoms and electrons so closely together that they interact very differently. With depth materials change. New ...

New scenery at Earth's core-mantle boundary found

Sep 02, 2010

(PhysOrg.com) -- Using a diamond-anvil cell to recreate the high pressures deep within the earth, researchers at the California Institute of Technology (Caltech) have found unusual properties in an iron-rich magnesium- and ...

Magnesium oxide: From Earth to super-Earth

Nov 22, 2012

The mantles of Earth and other rocky planets are rich in magnesium and oxygen. Due to its simplicity, the mineral magnesium oxide is a good model for studying the nature of planetary interiors. New work from ...

Lopsided Growth at the Earth's Core

Apr 21, 2010

What has twisted the Earth’s core so asymmetrically out of shape? That question has been a long-standing mystery for scientists, but two new studies are shining some light on the geodynamic processes that ...

Earth's inner core is melting... and freezing

May 18, 2011

The inner core of the Earth is simultaneously melting and freezing due to circulation of heat in the overlying rocky mantle, according to new research from the University of Leeds, UC San Diego and the Indian ...

Recommended for you

Climate impacts of changing aerosol emissions since 1996

1 hour ago

The re-distribution of anthropogenic aerosol emissions from Europe and North America towards China and India between 1996 and 2010 has surprisingly warmed rather than cooled the global climate. This result reinforces the ...

Hurricane churns towards Bermuda, to impact US

18 hours ago

A strengthening Hurricane Cristobal had Bermuda in its sights Tuesday, US meteorologists said, warning of heavy rain, high winds and life-threatening rip currents in Florida and beyond.

TRMM and Aqua satellites gaze into Hurricane Cristobal

18 hours ago

NASA's TRMM and Aqua satellites have been providing views of the outside and inside of Hurricane Cristobal as it heads for Bermuda. The National Hurricane Center posted a Tropical Storm Watch for Bermuda ...

Satellite shows Hurricane Marie about to swallow Karina

18 hours ago

Massive Hurricane Marie appears like a giant fish about to swallow tiny Tropical Depression Karina on satellite imagery today from NOAA's GOES-West satellite. Karina, now a tropical depression is being swept ...

NASA sees huge Hurricane Marie slam Socorro Island

18 hours ago

NASA's Terra satellite passed over Hurricane Marie when its eye was just to the west of Socorro Island in the Eastern Pacific. Marie's eye may have been near the island, but the storm extended several hundreds ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

gOnAd
2 / 5 (1) Dec 13, 2012
Hmmm, funny no mention how this relates to pallasite meteorites..