What may be the oldest patch of undisturbed oceanic crust on Earth has recently been identified by an Israeli scientist. Roi Granot, a professor at Ben Gurion University of the Nevev, estimates that the crust, which lies deep beneath the eastern Mediterranean Sea, may be 340 million years old -- making it 150 million years oldedr than the previous record holder.
Compared to continental crust, which can be billions of years old, oceanic crust is relatively young: It forms when hot magma wells up at oceanic ridges, and spreads slowly across the ocean floor, only to be recycled back into Earth's mantle because of its high density, before ultimately rising again as new magma.
The oldest piece of oceanic crust found to this point, off the east coast of Japan, is estimated at 190 million years old -- although a rare example of ocean crust being forced upward and onto land has been found in Greenland, part of a 3.5 billion-year-old chunk that is the oldest piece of Earth's crust ever found.
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As part of an effort to study the nature and age of the crust underlying the eastern Mediterranean, Granot and a team of researchers conducted four research cruises over the course of two years, crossing the area between Turkey and Egypt and towing sensors to search for magnetic signals. Such signals are a result of the magnetization of minerals in newly forming rocks when magma at a mid-ocean ridge axis cools; those magnetic minerals align themselves with the direction of Earth's magnetic field, and flip each time the field does.
"Changes in the magnetic field's orientation over time are recorded in the ocean floors, creating a unique barcode that provides a time stamp for crust formation," Granot said in a press release.
After two years of searching, Granot's efforts bore fruit, when his data revealed a series of magnetic stripes.
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"Here I am in the middle of the eastern Mediterranean and I see this beautiful feature that crosses the entire sea, from north to south," Granot told New Scientist. "That feature can only be created by oceanic crust."
By comparing the signals with modeling of plate tectonics, Granot determined that the roughly 60,000-square-mile piece of crust was approximately 340 million years old. That would place it at roughly the time that Earth's landmasses were combining to form the super-continent Pangaea, and therefore, may be a remnant of the ancient Tethys Sea. If so, it would suggest that that ocean formed some 50 million years earlier than previously thought -- or, Granot proposed, his discovery might be part of some other, unknown, ocean floor.