First asteroids found with Earthlike crust

The finding is the first from an asteroid with an Earthlike crust, the University of Maryland geochemists and other researchers reported in the journal Nature.

The discovery also represents the oldest example of rock with this composition ever found, they said.

The meteorites point "to previously unrecognized diversity" of materials formed early in the history of the solar system, write the authors, who are also from the University of Tennessee and the Carnegie Institution for Science.

"What is most unusual about these rocks is that they have compositions similar to Earth's andesite continental crust -- what the rock beneath our feet is made of," Maryland geologist James Day said.

"No meteorites like this have ever been seen before," he said.

Andesite is an igneous, volcanic rock that gets its name from the Andes mountain range in South America, where it is plentiful.

The two meteorites were discovered in Antarctica's Graves Nunatak Icefield in 2007, the scientists said.

They said the rocks are more than 4.52 billion years old and were formed during the birth of the solar system.

Their age, combined with the oxygen isotope data, "points to their origin from an asteroid rather than a planet," Day said.

Asteroids, sometimes called minor planets or planetoids, are bodies, primarily of the inner solar system, that are smaller than planets but larger than meteoroids, but exclude comets.