Geologists from Münster have found rock material from the Earth's proto-crust

The material was formed around four and a half to four billion years ago – in the Earth's so-called Hadean Eon. This is only the second find of its kind in the world, and it shows that certain areas in the upper sections of the Earth's crust can stay untouched for billions of years, thereby storing information from the Earth's earliest years. The researchers have published their results in the latest issue of the prestigious magazine “Nature”.

In the earliest period of its history – the Hadean Eon – the Earth was surrounded by an ocean of molten rock which slowly solidified. The scientists from the Institute of Mineralogy at WWU – Dr. Dewashish Upadhyay, Prof. Erik Scherer and Prof. Klaus Mezger – have demonstrated with their find that material from the Earth's proto-crust is still traceable in today's crust, even though this is in constant movement and rock material of varying ages has, in the course of time, been mixed in.

The only other find of this kind was made around a year ago in Canada and made the headlines at the time. “Every find that provides insights into the time the Earth was formed is virgin territory,” says Prof. Mezger. This explains why this second find is so significant.

The magmatic rocks come from the State of Orissa in India. They were formed from material that came into being over four billion years ago. About 1.5 billion years ago this melted and formed the new rocks in the upper sections of the Earth's crust at a depth of more than 40 kilometres. As a result of movements in the Earth's crust and weathering processes the rocks finally reached the Earth's surface, which is where they were found by the team of Münster researchers.

“As our Earth is a very active planet, geologically speaking,” says Prof. Mezger, “the rocks are constantly worked on, for example through weathering or melting. This means that the rock material to be found today on the Earth's surface is very old. The minerals making up these rocks are, however, much younger. It's a bit like baking a cake: you have the flour before you have the cake.” After this second find of rocks from primeval material the scientists now suspect that there is yet more of this material from the Hadean Eon on the Earth's surface – only no one has yet discovered it.

An additional factor is that any analysis of the rock samples is very elaborate. The scientists found proof of the enormous age of the material providing the basis for the much younger magmatic rocks by examining the abundance of a certain isotope of the element neodymium.

In the case of such old rock material this abundance differs from the known mean value for the Earth. “In future,” says Prof. Mezger, “it will be very interesting to pinpoint such old areas in the Earth's crust and take samples there. This would give us a better understanding of the history of the Earth's development in its formative years.”

References: Upadhyay D., Scherer E. and Mezger K. (2009): 142Nd evidence for an enriched Hadean reservoir in cratonic roots. Nature 459, 1118-1121 | doi:10.1038