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Scientists reveal the secret of the missing chemical element Niobium on Earth

Scientists from Cologne and Bonn have shown that the rare metal niobium had already moved towards the core of asteroids. The collisions of these asteroids with the Earth were responsible for its growth more than 4.6 billion years ago. / Publication in „Nature Geoscience“

The results of a team of scientists from the universities in Cologne and Bonn allow new insights in the growing periods of the young Earth more than 4.6 billion years ago. It has been established that the Earth has grown to its present size through collisions of asteroids. The recent study suggests that the metal cores of the asteroids immediately melted into the core of the Earth during these planetary collisions. During this process, considerable amounts of niobium that should have been concentrated in the silicate mantle of the Earth disappeared. ‘The missing niobium can be found in the metal core of the Earth, more than 2900 kilometers beneath the surface’, says geomechanic Carsten Münker from Cologne. ‘Our research shows that it had already moved towards the metal core of the asteroids’, adds his colleague Raul Fonseca from Bonn. The current findings of the team from Cologne and Bonn was published in the current issue of Nature Geoscience.

The early evolutionary history of the Earth more than 4.5 billion years ago is still not understood very well, because the oldest rocks are only around 4 billion years old. Geologists thus have to rely on indirect indicators to decode the Earth’s early history. Geological Events have left their chemical traces in rocks, for example in the form of an abnormally high or low level of rare trace elements or decay products of long lost radioactive isotopes. Such a trace is niobium, which only occurs in very low concentrations (one gram per ton of rocks or less). It has been known for about ten years that the outer silicate mantle of the Earth lacks around 20 percent of Niobium. The reason for this was unknown, however, speculations circled around the idea that those 20 percent of niobium got lost during the early geological history of the Earth.

Scientists from the Institute of Geology and Mineralogy in Cologne and the Steinmann Institute in Bonn could now solve this puzzle. They conducted extremely precise measurements of niobium in pieces of meteorites from the asteroid belt. ‘These asteroids are the only remains of our early solar system’, explains Dr. Toni Schulz, now at the University of Wien, who examined many of the precious meteorite probes for the recent study in advance. All bigger planets in the solar system developed through collisions of these asteroids.

The fact that niobium often occurs in the core of the asteroids in considerable amounts ‘does not correspond with the geological predictions’, says geochemist Münker from Cologne. ‘We always assumed that it only occurs in the outer shell of asteroids, not in the metallic core. Surprisingly, the results from our laboratories show that considerable amounts of niobium can move towards the metal core during the process of melting’, explains petrologist Dr. Raúl Fonseca from Bonn, who executed the laboratory experiments.

Media Enquiries:
Prof. Dr. Carsten Münker
Institut für Geologie und Mineralogie Köln
+49 221 470-3198
c.muenker(at)uni-koeln.de
   
Dr. Raúl Fonseca
Steinmann-Institut für Geologie, Mineralogie und Paläontologie Bonn
+49 228 73-9782
rfonseca(at)uni-bonn.de

Press und Communication Team:
Jürgen Rees
+49 221 470-3107
j.rees(at)uni-koeln.de

Original Publication:
Carsten Münker, Raul O.C. Fonseca, Toni Schulz: Silicate Earth’s missing Niobium may be sequestered into Asteroidal Cores. Nature Geoscience http://dx.doi.org/10.1038/ngeo3048