It has long been known that the inner core of the earth, a sphere consisting of a solid mass with a radius of about 1,200 km, is mainly made up of iron. However, seismic observations have shown that elastic waves pass more rapidly through this core in directions that are parallel to the earth’s axis of rotation than in directions parallel to the equator-a phenomenon that has not been previously explained. At the high temperatures that prevail in the core of the earth, these waves should pass at the same speed regardless of their direction.
In the present study, scientists from Uppsala University and KTH present an explanation for this puzzling characteristic. The publication is part of a series of articles published by the same research team in Nature and Science. Initially, in 2003, they published strong theoretical proof that the earth’s core assumes the so-called body-centered cubic crystal structure at high temperatures-a structure that despite its high degree of symmetry evinces a surprisingly high level of elastic anisotropy, that is, its elastic properties are contingent on direction. This theory about the crystal structure directly contradicted the then prevailing view, but since then the theory has found both experimental and theoretical support.
In this new study the researchers present simulations of how seismic waves are reproduced in iron under the conditions that prevail in the core of the earth, showing a difference of about 12 percent depending on their direction-which suffices as an explanation for the puzzling observations. First the trajectories of movement were calculated for several million atoms in strong interaction with each other. On this basis, the scientists were then able to determine that the progress of the sound waves was actually accurately described in the computer-generated model for iron under the conditions prevailing in the core of the earth.
“We found that the body-centered cubic structure of iron is the only structure that could correspond to the experimental observations,” says Börje Johansson, professor of condensed-matter theory at Uppsala University.
The earth’s heat balance, like its magnetic field, is dependent on the amount of heat that is stored in the inner core of the earth. These conditions, in turn, are dependent on the crystal structure of the iron in the inner core. Previously these estimates were based on models deriving from the hexagonal structure of iron in the inner core. The Swedish scientists’ discovery will now entail a critical revaluation of the cooling off of the earth and of the stability of its magnetic field.
“This study opens new perspectives for our understanding of the earth’s past, present, and future,” says Natalia Skorodumova, a researcher at the Department of Physics and Materials Science.
In their studies these researchers have used models based on the so-called density-functional theory for which Walter Kohn was awarded the 1999 Nobel Prize. The calculations were carried out using the most powerful parallel supercomputers in existence, in Stockholm and Linköping.
The body-centered cubic crystal structure forms a cube with atoms in each corner and a further atom in the middle of this cube. It is oriented in such a way that its great diagonal is directed along the earth’s axis of rotation, which makes it possible for the iron to evince sound propagations with the velocities observed.
Boerje Johansson | EurekAlert!
GPM sees deadly tornadic storms moving through US Southeast
01.12.2016 | NASA/Goddard Space Flight Center
Cyclic change within magma reservoirs significantly affects the explosivity of volcanic eruptions
30.11.2016 | Johannes Gutenberg-Universität Mainz
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy