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EMBARGOED BY Science MagazineFOR RELEASE ON Thursday, March 22, 2007 11:00 AM PDTThursday, March 22, 2007 Scripps/UCSD Geophysicist Among International Team Finding Evidence of First Plate Tectonics 3.8 Billion Years Ago Observations indicate that plate tectonics began before any currently known structural geological record on Earth Scripps Institution of Oceanography / University of California, San Diego Identification of the oldest preserved pieces of Earth's crust in southern Greenland has provided evidence of active plate tectonics as early as 3.8 billion years ago, according to a report by an international team of geoscientists in the March 23 edition of Science magazine. Geophysicist Hubert Staudigel in his lab with a seafloor pillow lava. "The fact that this rock structure is so well preserved is particularly lucky," Staudigel said. "The materials were formed as seafloor along a spreading center and accreted to a continental plate and just stuck there, surviving almost unscathed for as long as 3.8 billion years." Coauthors of the report are Harald Furnes of University of Bergen, Norway; Maarten de Wit of University of Cape Town, South Africa; Minik Rosing of the University of Copenhagen, Denmark; and Karlis Muehlenbachs of the University of Alberta, Canada. The study focuses on an area near the southwestern coast of Greenland where there is a rare outcrop of ancient rock, called the Isua Supracrustal Belt, which have been dated at 3.8 billion years old. The Isua rocks are ophiolites, which have a green hue from the chlorite minerals within them and are found in all major mountain belts, usually located in areas associated with volcanism and plate tectonics. The Isua deposits were first described in the 1960s. They also have been found to contain fossilized evidence of the earliest bacterial life on Earth, also about 3.8 billion years old, in studies conducted in 1999 by Minik Rosing.  Well preserved pillow lavas are an indication of ancient plate tectonics at Isua Supracrustal Belt in southwestern Greenland. "To what extent one is able to see an original structure in a highly deformed rock depends basically on the experience of the observer," Furnes said. "In our case we knew what we were looking for, and all of us who did the field work have reasonably good experience with identifying pillow lavas and associated dikes." The finding of ophiolites in the oldest known rock structures leads the scientists to believe that such rocks have formed throughout Earth's nearly 4.5 billion year history, according to de Wit. "Our work shows that some form of seafloor spreading and oceanic crust formation occurs as far back in history as geological records go," de Wit said. Rosing said, "Our paper describes large-scale structural relationships that show the ancient oceanic crust was comparable to the modern crust in its structure and composition and that a section of ancient oceanic crust could be preserved by uplifting onto stable crust, similar to how more modern ophiolite complexes have formed." The paper also sheds light on the ongoing debate about the oxygen isotope composition of seawater through geological time periods. The reactions of seafloor and seawater largely control the ocean's oxygen isotope makeup, but scientists have been polarized between those that maintain the oxygen isotope content has remained relatively constant and those that argue for variation. According to Muehlenbachs, this work shows that the early ocean had the same or slightly heavier oxygen isotope composition as that of the modern ocean. "We can conclude from the oxygen isotope analyses of the pillows and dIkes that the earliest ocean had already chemically reacted with the seafloor," Muehlenbachs said. "This has great implications to the historical chemical composition of the oceans and may have played a role in the evolution of life."  The striations in a rock outcropping shows the layers of sheeted dikes created by ancient seafloor spreading at the Isua Supracrustal Belt in southwestern Greenland. The Norwegian Research Council, the Nordic Center for Earth Evolution, GeoForschungsZentrum Potsdam, Agouron Institute and the National Sciences and Engineering Research Council of Canada provided funding for the research. Reference: "A Vestige of Earth's Oldest Ophiolite," Science, 23 March 2007, http://www.sciencemag.org/ Scripps Institution of Oceanography: http://scripps.ucsd.edu Scripps News: http://scrippsnews.ucsd.edu # # # Note to broadcast and cable producers: University of California, San Diego provides an on-campus satellite uplink facility for live or pre-recorded television interviews. Please phone or e-mail the media contact listed above to arrange an interview. Scripps Institution of Oceanography, at University of California, San Diego, is one of the oldest, largest and most important centers for global science research and education in the world. The National Research Council has ranked Scripps first in faculty quality among oceanography programs nationwide Now in its second century of discovery, the scientific scope of the institution has grown to include biological, physical, chemical, geological, geophysical and atmospheric studies of the earth as a system. Hundreds of research programs covering a wide range of scientific areas are under way today in 65 countries. The institution has a staff of about 1,300, and annual expenditures of approximately $155 million from federal, state and private sources. Scripps operates one of the largest U.S. academic fleets with four oceanographic research ships and one research platform for worldwide exploration. |
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