What Goes On Underneath Your Feet? Virtual Trip Inside The Earth

July 16, 2004
What Goes On Underneath Your Feet? View of the Earth and its inner structure. (Copyright: Insign and ESRF)

It is generally assumed that heat from Earth’s core and mantle, due to the low thermal conductivity of the latter, is transferred to the outer part mainly by convection. This implies swirling movement of an immense amount of hot material, which is behind the dynamics of Earth’s interior. Understanding the details of this is of great interest since it can explain natural phenomena such as earthquakes, volcanoes, movements of tectonic plates and formation of mountains. A team from the University of Paris and the European Synchrotron Radiation Facility (ESRF) have found out that iron-bearing magnesium silicate perovskite, the Earth’s most abundant mineral, transforms, when pressure is applied, to a state where radiation could play a far more important role in heat transfer in the lowermost part of the mantle. This would change our vision of the dynamics of the deep Earth and would suggest that the material at these depths is more static than currently thought.

These results are published today in 'Science'. They are based on experiments conducted at the ESRF, which, in addition to its high quality X-ray beam, allowed the conditions inside the Earth to be reproduced on the sample.

Earth’s lower mantle is formed mainly by two components: magnesium silicate perovskite and magnesiowüstite. The first one, the subject material of this research, occupies 80% of the mantle. Therefore, it is indispensable to explore how this behaves at high pressure. Iron in perovskite is in a magnetic (high-spin) state at atmospheric pressure, the electronic properties of which are mainly responsible for this mineral being opaque to infrared radiation (heat). The team performed the experiment at various pressures and found electronic transitions which show that iron becomes non-magnetic (low-spin) at significantly lower pressure than previously thought. This pressure (or depth) is consistent with that of the D" layer, the deepest part of the lower mantle which is also the most mysterious and uncharacterised layer in the Earth, which separates Earth’s liquid metallic core below from the solid silicate mantle above.

The most striking consequence of the revealed electronic transition is an increased transparency of the material to the near-infrared radiation (where the core and mantle radiate most of their thermal energy). The sample became more transparent to heat above 70 GPa (bottom third of the mantle) and almost completely transparent above 120 GPa (D? layer above the core-mantle boundary); this is more than one million times greater than atmospheric pressure. Increased transparency is the reason why these researchers suggest that in the deep Earth, radiation plays a larger role with respect to convection in transferring heat.

During the experiment, the researchers took a virtual trip inside the Earth by reproducing the conditions of Earth’s mantle at the ESRF. They placed the sample of iron-bearing perovskite between the two diamond tips of a diamond-anvil cell and subjected them to pressures from 20 to 145 GPa. By using x-rays, they could extract information from the sample and its behaviour under those conditions.

Source: ESRF

Explore further: Cracking open diamonds for messages from the deep earth

Related Stories

Cracking open diamonds for messages from the deep earth

August 25, 2015

Geochemist Yaakov Weiss deals in diamonds. Not the brilliant jewelry-store kind, but the flawed, dirty-looking ones used more for industry than decoration. Gem-grade diamonds are generally pure crystallized carbon, ...

What is the Earth's average temperature?

August 19, 2015

Earth is the only planet in the solar system where life is known to exists. Note the use of the word "known", which is indicative of the fact that our knowledge of the solar system is still in its infancy, and the search ...

The dwarf planet Ceres

August 12, 2015

The asteroid belt is a pretty interesting place. In addition to containing between 2.8 and 3.2 quintillion metric tons of matter, the region is also home to many minor planets. The largest of these, known as Ceres, is not ...

The planet Mercury

August 6, 2015

Mercury is the closest planet to our sun, the smallest of the eight planets, and one of the most extreme worlds in our solar systems. Named after the Roman messenger of the gods, the planet is one of a handful that can be ...

The Planet Saturn

August 3, 2015

The farthest planet from the Sun that be observed with the naked eye, the existence of Saturn has been known for thousands of years. And much like all celestial bodies that can be observed with the aid of instruments – ...

Neptune's moon of Triton

July 29, 2015

The planets of the outer solar system are known for being strange, as are their many moons. This is especially true of Triton, Neptune's largest moon. In addition to being the seventh-largest moon in the solar system, it ...

Recommended for you

New Horizons team selects potential Kuiper Belt flyby target

August 29, 2015

NASA has selected the potential next destination for the New Horizons mission to visit after its historic July 14 flyby of the Pluto system. The destination is a small Kuiper Belt object (KBO) known as 2014 MU69 that orbits ...

Interactive tool lifts veil on the cost of nuclear energy

August 24, 2015

Despite the ever-changing landscape of energy economics, subject to the influence of new technologies and geopolitics, a new tool promises to root discussions about the cost of nuclear energy in hard evidence rather than ...

0 comments

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.