Gradients in the Earth's outermost core

Dec 08, 2010
Gradients in the Earth's outermost core

Evidence that the outermost portion of the Earth’s core is stratified is provided by earthquake data reported by scientists at the University of Bristol this week in Nature.

The Earth's core is composed mainly of iron, but it is also known to contain a small amount of lighter elements, such as oxygen and sulphur. As the ’s inner core solidified, it is thought to have expelled most of these light elements, which then migrated up through the liquid outer core, perhaps becoming concentrated in the outermost portion of the core, near the core/mantle boundary.

Professor George Helffrich and Satoshi Kaneshima observed seismic waves which travelled through the outermost core, from earthquakes in South America and the southwestern Pacific Ocean, recorded at arrays of seismometers in Japan and northern Europe.

The speeds at which seismic waves travelled through the outer core at different depths suggest that it is not a homogenous liquid, but that the uppermost 300 kilometres or so of the core is stratified, with the portion nearest the core/mantle boundary containing up to five per cent by weight light elements.

This stratification would affect temperature gradients in the outermost core and have implications for our understanding of the thermal evolution of the core and lowermost mantle.

Explore further: New study confirms water vapor as global warming amplifier

More information: Outer-core compositional stratification from observed core wave speed profiles by George Helffrich and Satoshi Kaneshima in Nature.

Related Stories

The Earth's hidden weakness

May 28, 2010

(PhysOrg.com) -- Three thousand kilometres beneath our feet, the Earth's solid rock gives way to the swirling liquid iron of the outer core.

A speed gun for the Earth's insides

Oct 27, 2010

(PhysOrg.com) -- Researchers at the University of Bristol reveal today in the journal Nature that they have developed a seismological 'speed gun' for the inside of the Earth. Using this technique they will b ...

Scientists probe Earth's core

Apr 28, 2010

We know more about distant galaxies than we do about the interior of our own planet. However, by observing distant earthquakes, researchers at the University of Calgary have revealed new clues about the top ...

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 ...

Recommended for you

New research reveals Pele is powerful, even in the sky

1 hour ago

One might assume that a tropical storm moving through volcanic smog (vog) would sweep up the tainted air and march on, unchanged. However, a recent study from atmospheric scientists at the University of Hawai'i ...

Image: Wildfires continue near Yellowknife, Canada

1 hour ago

The wildfires that have been plaguing the Northern Territories in Canada and have sent smoke drifting down to the Great Lakes in the U.S. continue on. NASA's Aqua satellite collected this natural-color image ...

Excavated ship traced to Colonial-era Philadelphia

2 hours ago

Four years ago this month, archeologists monitoring the excavation of the former World Trade Center site uncovered a ghostly surprise: the bones of an ancient sailing ship. Tree-ring scientists at Columbia ...

Tropical tempests take encouragement from environment

3 hours ago

Mix some warm ocean water with atmospheric instability and you might have a recipe for a cyclone. Scientists at Pacific Northwest National Laboratory and the Atlanta Oceanographic and Meteorological Laboratory ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Graeme
not rated yet Dec 12, 2010
Some of these layers could be a form of sedimentary deposit, where something (perhaps iron oxide) crystallizes out from the iron liquid, and floats to the top of the core and forms a slushy dross just below the mantle. Over time this should become compressed and more solid as the molten iron is squeezed out of the pores.

Another interesting possibility is whether a form of life could arise at the core boundary, using some different chemistry. However where would it get energy from?