Island Chains May Hold Key to Age of Earth's Continents
Geologists have long been trying to answer the question of exactly when Earth's continents formed. . Now, new research suggests that island arcs might help pin down the continents' ages.
The initial findings of the research suggest the continents could be several hundred million years older than previously thought.
The continental crust is the principal storehouse of changes in conditions on Earth for the last 4.4 billion years, such as the development of life and climate. Revisions in the ages of continental crust formation could therefore affect our understanding of many fields, said geochemist Bruno Dhuime at the University of Bristol in England.
Island arcs are curved archipelagos of volcanoes located close to converging tectonic plates. These kinds of plate margins are the birthplace of at least 80 percent of the part of the Earth's crust that makes up the continents, and they are where new continental crust continues to be made.
To see when the continental crust was created, scientists are measuring what isotopes of certain chemical elements are found within rocks and minerals. Isotopes are variants of elements that have different numbers of neutrons in their atomic nuclei; the isotope composition of certain elements in rocks can shed light on how old they are.
It turns out that isotope composition of island arcs could more closely represent what new crust in general is like than isotopes from rocks elsewhere along converging tectonic plate boundaries, as island arcs are not as prone to contamination from pre-existing continental crust.
By analyzing isotopes of the element hafnium in 13 modern island arcs worldwide including the Aleutian Islands in Alaska and the Tonga archipelago in the South Pacific scientists now find the continental crust arose up to 300 million years earlier than was previously thought.
Dhuime and his colleagues detailed their analysis in the Jan. 14 issue of the journal Science.
