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What lies beneath: new research looks deep into the centre of the Earth


For immediate release
Thursday 19 January 2006

New research published today on the evolution of volcanoes sheds light on what lies deep beneath the Earth's surface.

The research, published in Nature, suggests that the plume of hot material that provides Hawaii's volcanoes with its continuous supply of molten lava originates from a depth of almost 3000 km, at the border between the Earth's core and its rocky mantle. This is far deeper than had been thought possible by many scientists.

Plumes are hot, narrow currents that well up in the mantle and which are responsible for the formation of long chains of volcanoes such as those of the Hawaiian Islands. The question of whether plumes rise from the boundary between the core of the Earth and the mantle that surrounds it, or from a much shallower boundary layer within the mantle, has been hotly debated for more than a quarter of a century.

The plume of hot material that provides Hawaii's volcanoes with its supply of molten lava is believed to come from a depth of almost 3000 km

The new research proved the presence of material from the Earth's core by using a new type of mass spectrometer to analyse the isotope signature of the element thallium in Hawaiian volcanic rocks. Isotope analysis can reveal the physical, chemical and biological processes to which a single element has been subjected.

Dr Mark Rehkamper Opens in new window, from Imperial College London's Department of Earth Sciences and Engineering and the senior author of the research, said: "It is only recently that scientists have developed the ability to analyse these volcanic rocks in enough detail to reveal exactly where in the Earth's interior they came from. The previous evidence has unfortunately been quite ambiguous but our new thallium isotope results are now able to conclusively rule out some of the alternative models. What remains is clear evidence of interaction between the Earth's core and mantle."

The evidence that plumes originate at the core-mantle boundary suggests that the mantle constitutes one big convective system, like a soup being continuously stirred, rather than being made up of several layers. It also reveals that sedimentary material from the Earth's surface is subducted into the mantle to make its way back to the surface in the plumes, over time periods of one or two billion years.

Previous analysis of volcanic rocks from Hawaii looked at the isotope signature of the element osmium in them and appeared to show that material from the earth's core was present. However, some scientists argued that the presence of core material was due to contamination of the mantle plume with sediments from the Earth's surface. The new research demonstrates that the quantities of sedimentary material were much too low for this to be the case.

The research was carried out by scientists at Imperial College London, ETH Zurich, Macquarie University, the Australian National University and the University of Oxford. It was funded by ETH Zurich, Schweizerische Nationalfonds and the Danish Research Agency.

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For further information please contact:

Laura Gallagher
Press Officer
Communications Division
Imperial College London
Tel: +44 (0)20 7594 6702
Mobile: +44 (0)7803 886248
E-mail: l.gallagher@imperial.ac.uk

Notes to editors:

1. 'Thallium isotopic evidence for ferromanganese sediments in the mantle source of Hawaiian basalts' Nature, 19 January 2006

Sune G. Nielsen1,2, Mark Rehkamper1,3, Marc D. Norman4, Alex N. Halliday1,5, Darrell Harrison1

1 Department of Earth Sciences, ETH Zurich, Sonneggstrasse 5, 8092 Zurich, Switzerland. 2GEMOC.

2 Department of Earth and Planetary Sciences, Macquarie University, 2109 New South Wales, Australia.

3 Department of Earth Science and Engineering, Imperial College, London SW7 2AZ, UK.

4 Research School of Earth Sciences, Australian National University, Canberra, Australian Capital Territory 0200, Australia.

5 Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK.

2. Consistently rated in the top three UK university institutions, Imperial College London is a world leading science-based university whose reputation for excellence in teaching and research attracts students (11,000) and staff (6,000) of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and management and delivers practical solutions that enhance the quality of life and the environment - underpinned by a dynamic enterprise culture.
Website: www.imperial.ac.uk

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