North American continent is a layer cake: Study

A new study by seismologists at the University of California, Berkeley, has revealed that the North American continent is not one thick, rigid slab, but a layer cake of ancient, 3 billion-year-old rock on top of much newer material probably less than 1 billion years old.

The finding explains inconsistencies arising from new seismic techniques being used to explore the interior of the earth, and illuminates the mystery of how the Earth's continents formed.

"This is exciting because it is still a mystery how continents grow," said study co-author Barbara Romanowicz, director of the Berkeley Seismological Laboratory and a UC Berkeley professor of earth and planetary science.

"We think that most of the North American continent was constructed in the Archean (eon) in several episodes, perhaps as long ago as 3 billion years, though now, with the present regime of plate tectonics, not much new continent is being formed," Romanowicz added.

The study has been reported in the August 26 issue of Nature.