Unique Chemistry Reveals Eruption of Ancient Materials Once at Earth’s Surface

New study supports theory that Earth's earliest crust was folded back into its mantle and returned to the surface in volcanoes. An international team of researchers, including Scripps Institution of Oceanography, UC San Diego, geochemist James Day, has found new evidence that material contained in oceanic lava flows originated in Earth's ancient Archean crust. These findings support the theory that much of the Earth's original crust has been recycled by the process of subduction, helping to explain how the Earth has formed and changed over time. The Archean geologic eon, Earth's second oldest, dating from 3.8 to 2.5 billion years ago, is the source of the oldest exposed rock formations on the planet's surface. (Archean rocks are known from Greenland, the Canadian Shield, the Baltic Shield, Scotland, India, Brazil, western Australia, and southern Africa. Although the first continents were formed during the Archean eon, rock of this age makes up only around seven percent of the world's current crust. "Our new results are important because they provide strong evidence not only to tie materials that were once on Earth's surface to an entire cycle of subduction, storage in the mantle, and return to the surface as lavas, but they also place a firm time constraint on when plate tectonics began; no later than 2.5 billion years ago," said Day.