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RAS PN 08/36: Mystery of ancient supercontinent revealed

Last Updated on Tuesday, 06 April 2010 17:29
Published on Tuesday, 22 April 2008 00:00
In a paper published in this month’s ‘Geophysical Journal International’, Dr Graeme Eagles from the Earth Sciences Department at Royal Holloway, University of London, reveals how one of the largest continents ever to exist met its demise.

ROYAL ASTRONOMICAL SOCIETY PRESS INFORMATION NOTE

Date: 22 April 2008
For immediate release
Ref.: PN 08/36

Issued by:

Dr Robert Massey
RAS Press Officer
Royal Astronomical Society
Burlington House
Piccadilly
London W1J 0BQ
Tel: +44 (0)7734 3307
Mob: +44 (0)794 124 8035
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

RAS website: www.ras.org.uk

MYSTERY OF ANCIENT SUPERCONTINENT REVEALED

In a paper published in this month’s ‘Geophysical Journal International’, Dr Graeme Eagles from the Earth Sciences Department at Royal Holloway, University of London, reveals how one of the largest continents ever to exist met its demise.

Gondwana was a ‘supercontinent’ that existed between 500 and 180 million years ago. For the past four decades, geologists have debated how Gondwana eventually broke up, developing a multitude of scenarios which can be loosely grouped into two schools of thought – one theory claiming the continent separated into many small plates, and a second theory claiming it broke into just a few large pieces. Dr Eagles, working with Dr Matthais König from the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, has devised a new computer model showing that the supercontinent cracked into two pieces, too heavy to hold itself together.

Gondwana comprised of most of the landmasses in today’s Southern Hemisphere, including Antarctica, South America, Africa, Madagascar, Australia-New Guinea, and New Zealand, as well as Arabia and the Indian subcontinent of the Northern Hemisphere. Between around 250 and 180 million years ago, it formed part of the single supercontinent ‘Pangea’.

Evidence suggests that Gondwana began to break up at around 183 million years ago. Analysing magnetic and gravity anomaly data from some of Gondwana’s first cracking points – fracture zones in the Mozambique Basin and the Riiser-Larsen Sea off Antarctica – Dr Eagles and Dr König reconstructed the paths that each part of Gondwana took as it broke apart.  The computer model reveals that the supercontinent divided into just two large, eastern and western plates. Approximately 30 million years later, these two plates started to split to form the familiar continents of today’s Southern Hemisphere.

‘You could say that the process is ongoing as Africa is currently splitting in two along the East African Rift,’ says Dr Eagles. ‘The previously held view of Gondwana initially breaking up into many different pieces was unnecessarily complicated. It gave fuel to the theory that a plume of hot mantle, about 2,000 to 3,000 kilometres wide, began the splitting process. A straight forward split takes the spotlight off plumes as active agents in the supercontinent’s breakup, because the small number of plates involved resembles the pattern of plate tectonics in the rest of Earth’s history during which plumes have played bit parts.’

According to Dr Eagles and Dr König’s study, because supercontinents like Gondwana are gravitationally unstable to begin with, and have very thick crusts in comparison to oceans, they eventually start to collapse under their own weight.

Says Dr Eagles, ‘These findings are a starting point from which more accurate and careful research can be made on the supercontinent. The new model challenges the positions of India and Sri Lanka in Gondwana which have been widely used for the past 40 years, assigning them very different positions in the supercontinent. These differences have major consequences for our understanding of Earth.’

IMAGES

These are available from Dr Eagles (contact details below)

Captions:

Figure 1

An image of gravity anomalies over the oceans that formed as parts of Gondwana moved apart, assembled using satellite data. Image: Graeme Eagles (Royal Holloway, University of London), David Sandwell (Scripps Institution of Oceanography), Walter Smith (NOAA Laboratory for Satellite Altimetry).

Figure 2

Image showing the movement of Gondwana over millions of years. Image: Graham Eagles (Royal Holloway, University of London).

NOTES FOR EDITORS

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

CONTACTS

Dr Graeme Eagles
Department of Earth Sciences
Royal Holloway, University of London
Egham
Surrey TW20 0EX
Tel: +44 (0)1784 443890
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Simon Doyle
Press and Communications Assistant
Royal Holloway, University of London
Egham
Surrey TW20 0EX
Tel: +44 (0)1784 443552
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.