[meteorite-list] Melting Asteroids and the Building Blocks of Early Earth

[Ron Baalke]

Media Relations Office
Communications Group
The Open University
Milton Keynes, U.K.

Media contact:
Louis De La Forêt, +(44) 1908 653256

Academic contact:
Dr Richard Greenwood, +(44) 1908 654107
Dr Ian Franchi, +(44) 1908 655173

EMBARGO 1800 BST 15 June 2005

Melting asteroids and the building blocks of early Earth

Important new research documenting how the Earth formed from melted 
asteroids 4.5 billion years ago is published in the 16 June issue of 
Nature. The paper was written by Dr Richard Greenwood and Dr Ian Franchi 
of the Open University's Planetary and Space Sciences Research Institute 
(PSSRI).

"This research is important, Dr Greenwood says, "because it demonstrates 
that events and processes on asteroids during the birth of the Solar 
System determined the present-day composition of our Earth."

Immediately following the formation of our Solar System 4.5 billion years 
ago, small planetary bodies formed, with some melting to produce volcanic 
and related rocks. The OU researchers analysed meteorites to see how 
processes on asteroids may have contributed to the formation of Earth.

In their paper "Widespread magma oceans on asteroidal bodies in the early 
Solar System" Drs Greenwood and Franchi show that some asteroids 
experienced large-scale melting, with the formation of deep magma oceans. 
Such melted asteroids would have become layered with lighter rock forming 
near the surface, while denser rocks were deeper in the interior. Since 
large bodies, such as Earth, grew by incorporation of many such smaller 
bodies these important results shed new light on the processes involved in 
building planets.

The researchers suggest that in the chaotic, impact-rich environment of 
the early Solar System, significant amounts of the outer layers of these 
melted asteroids would have been removed prior to becoming part of the 
growing Earth. This process is a better explanation for the composition of 
the Earth than earlier theories which called for large amounts of light 
elements in the Earth's dense core, or unknown precursor materials. The 
Open University researchers point to recent astronomical observations 
which show that these processes are also important in other planetary 
systems, such as that around the star Beta Pictoris.

Resources

* http://www.nature.com/nature/journal/v435/n7043/index.html
* http://cepsar.open.ac.uk/index.htm