Low density of Earth's core due to oxygen and silicon impurities

Jan 29, 2013

During accretion and differentiation of the Earth, chemical interactions in a silicate magma ocean and liquid iron drove silicon and oxygen impurities into what went on to become the liquid outer core. Contrasting with previous research, which suggested that silicon and oxygen would only appear in very low concentrations (less than 1 percent by weight) in the liquid iron, Tsuno et al. find that at the base of a magma ocean 1,200 kilometers (750 miles) deep, these light elements could reach concentrations as high as 5 percent oxygen and 8 percent silicon by weight, simultaneously. Such impurity levels would decrease the density of the outer core, accounting for the so-called "density deficit" identified in previous research, whereby the outer core is roughly 10 percent less dense than a pure iron-nickel alloy.

The researchers also propose that at the present-day core-mantle boundary, high temperatures would drive additional silicon and oxygen into the core, creating a light, element-rich, buoyant layer on the top of the . They suggest that evidence for such a layer may have been observed in seismic studies.

Using a multianvil press, the authors drove a mixture of iron, magnesium silicate, , and the iron oxide wüstite to 25 gigapascals (6.2 million pounds per square inch) of pressure and temperatures from 2,700 to 3,080 Kelvin (4,400 to 5,084 degrees Fahrenheit). They find that at temperatures below 3,000 Kelvin (4,940 degrees Fahrenheit), silicon and oxygen in the iron melt were mutually exclusive, with concentrations not rising above the low levels identified in previous research.

Above 3,000 Kelvin (4,940 degrees Fahrenheit), however, they find that the presence of oxygen actually enhanced the partitioning of silicon into the iron, with the concentrations of both silicon and oxygen increasing.

Explore further: Pre-1950 structures suffered the most damage from August 2014 Napa quake

More information: Simultaneous partitioning of silicon and oxygen into the Earth's core during early Earth differentiation, Geophysical Research Letters, doi: 10.1029/2012GL054116, 2013 http://onlinelibrary.wiley.com/doi/10.1029/2012GL054116/abstract

add to favorites email to friend print save as pdf

Related Stories

Earth's outer core deprived of oxygen: study

Nov 23, 2011

The composition of the Earth's core remains a mystery. Scientists know that the liquid outer core consists mainly of iron, but it is believed that small amounts of some other elements are present as well. Oxygen ...

Gradients in the Earth's outermost core

Dec 08, 2010

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.

Oxygen to the core

Jan 10, 2013

(Phys.org)—An international collaboration including researchers from Lawrence Livermore National Laboratory has discovered that the Earth's core formed under more oxidizing condition's than previously proposed.

Ironing out the details of the Earth's core

Dec 20, 2011

(PhysOrg.com) -- Identifying the composition of the earth's core is key to understanding how our planet formed and the current behavior of its interior. While it has been known for many years that iron is ...

Recommended for you

Lightning plus volcanic ash make glass

13 hours ago

In their open-access paper for Geology, Kimberly Genareau and colleagues propose, for the first time, a mechanism for the generation of glass spherules in geologic deposits through the occurrence of volcan ...

A new level of earthquake understanding

18 hours ago

As everyone who lives in the San Francisco Bay Area knows, the Earth moves under our feet. But what about the stresses that cause earthquakes? How much is known about them? Until now, our understanding of ...

Combined Arctic ice observations show decades of loss

21 hours ago

It's no surprise that Arctic sea ice is thinning. What is new is just how long, how steadily, and how much it has declined. University of Washington researchers compiled modern and historic measurements to ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.