3.8 Billion-Year-Old Rock Sequence Found in Greenland Revises Tectonic Timeline

Rocks found in southwestern Greenland—dated at 3.8 billion years old—confirm plate tectonics on early Earth. [Image © Science]

A 3.8 billion-year-old sequence of rocks from Greenland is helping scientists pinpoint when the Earth's plate tectonics system kicked into gear, according to new research in the 23 March issue of Science.

Found on the Isua supracrustal belt (ISB) in southwestern Greenland, newly found material is composed of igneous oceanic crust that formed when two tectonic plates separated at a mid-oceanic spreading ridge. As the two plates separated, magma was pushed up through the plate boundaries creating the new oceanic crust.

Millions of years later, that oceanic crust got scraped off its tectonic plate when one plate dove beneath another at a subduction zone. This caused the sequence of rocks to become uplifted through the continental crust of Greenland, a clear indication of tectonics.

Harald Furnes, professor of geology at the University of Bergen in Norway, and colleagues believe that this uplifted ocean crust—ophiolite—suggests that plate tectonics occurred early in Earth's history rather than just in the latter half of its 4.5 billion-year existence.

"The associated rocks [and] their compositions make a ~3.8-billion-year-old ophiolite, which in turn has strong implications about the early tectonic and geochemical evolution of Earth," the authors write.

While the authors wish to study the area more thoroughly to learn more about its history, they believe "the ISB preserves vestiges of Earth's oldest ophiolite and oceanic crust."

Kathy Wren and Benjamin Somers

23 March 2007