Inner earth core with special crystal structure
Previously unknown phase changes old ideasRead out
The inner core of the earth is obviously made up of an iron-nickel alloy with a special crystal structure. As scientists report in the latest issue of the science journal Science, experimental and theoretical studies for the first time revealed the existence of a so-called space-centered cubic phase of the alloy. This realization could also affect previous ideas about the liquid outer core.
The Earth's core, whose outer edge is 2, 900 kilometers below us, is by far the most inaccessible place on our planet. Although spaceships have now reached the outer planets of our solar system hundreds of millions of miles away, on Earth the deepest hole has only reached a depth of twelve kilometers. Not only is it impossible to extract samples from the Earth's core, the researchers do not even expect to ever have material from there for investigation.
Earth's interior still enigmatic
So far, only seismic investigations allow indirect observations of the Earth's core. Since the structure of the earth is very complex, seismic investigations require considerable amounts of data, which have to be inserted into appropriate models. Computer-aided and especially experimental simulations are made more difficult by the fact that pressures in the earth's core of over 140 gigapascals - corresponding to 1, 400, 000 atmospheres - and temperatures above 3, 000 degrees Celsius prevail. For these reasons, basic properties of the Earth's core continue to be difficult to research and controversial.
Recent research reveals a number of unusual and enigmatic phenomena regarding the properties and dynamics of the Earth's core. These include, for example, the discovery of so-called anisotropy in the interior of the nucleus: seismic waves propagate faster along the axis between the poles of the earth than in the equator direction. In addition, there is evidence for a different rotational behavior of the inner core and the rest of the earth. The Earth's magnetic field is closely linked to the dynamic processes in the Earth's core. display
Conditions as at 4, 000 kilometers depth
An international team of scientists from Germany, Sweden and the USA with the participation of a group of scientists led by Leonid Dubrovinsky of the Bavarian Geoinstitute of the University of Bayreuth has now extensively and experimentally explored an iron-nickel alloy with ten percent nickel at high pressures and temperatures. By combining the diamond stamping cell technique with electrical and laser-based heating methods, the scientists were able to expose the sample to pressures of more than 225 gigapascals and temperatures in excess of 3, 200 degrees Celsius. These experimentally generated conditions in the laboratory would be found in the Earth's interior at a depth of 4, 000 kilometers.
Under such extreme conditions, the alloy used abruptly changes in the values of electrical resistance. X-ray diffraction analyzes reveal a phase transition from the known hexagonal close-packed structure to a new cubic body-centered phase with a reduced density of about two percent. The scientists conclude that light elements are not required (or only in very small proportions) to confirm the density of the inner core as determined by seismic methods. In other words, the inner core of the Earth may consist solely of an iron-nickel alloy.
Modification of previous ideas
Not only could this result necessitate new interpretations of the physical and dynamic properties of the solid inner core, it could also affect our ideas about the liquid outer core. If structural changes occur in the liquid iron-nickel alloy, this could lead to other density values as well as the nature of the distribution of light elements such as silicon, magnesium, aluminum, and sodium in different ways structured areas of the outer core.
(University of Bayreuth, 02.07.2007 - NPO)