Researchers from the University of Texas at Austin Jackson School of Geosciences may have discovered that water likely pierces the crust and upper mantle of the Earth where new crust is created. Lead researcher Nick Dygert’s results supports the Sheeted Sill hypothesis which theorizes that water cools magma at various oceanic depths of the Earth and forms new crust layers. Dygert is a postdoctoral fellow in the Department of Geological Sciences joined by his colleagues, Peter Kelemen and Yan Liang of Columbia and Brown universities. Their findings were recently published in Earth and Planetary Science Letters.
Water, seeping into the Earth’s crust and upper mantle, helps form new crust at places on the surface where the oceans spread – most likely at places where plates meet. The crust, which can vary in depth from three miles to 40 miles is the thinnest at the ocean level. The mantle, which is underneath is almost 2,000 miles deep, making it the thickest part layer of the Earth. At the center of the Earth is the core which is made of iron and nickel and is nearly 5,700 Kelvins.
In a press release from the University of Texas, Dygert referred to the two battling theories about crust formation: the Sheeted Sill hypothesis and the Gabbro Glacier theory. Dygert’s discovery seems to support the Sheeted Sill hypothesis which theorize that new crust is created by ocean water that cools “small magma deposits” at ocean levels. The competing theory, Gabbro Glacier hypothesis, conjectures that magma cools as it moves slowly from the magma chamber, forming new crust.
The team of researchers studied samples from the mantle found in a canyon in the Oman on the southeastern coast of the Arabian Peninsula. In the peninsula, the team walked the canyon examining the walls that were like the “Earth’s interior,” Kelemen said. Also in the canyon, the team were also able to examine rocks that were likely formed on the ocean’s floor. Liang developed a new type of geothermometer for the study that could note the “maximum temperature a rock had attained before it cooled.” Using the geothermometer, the team could determine the rock’s formation rather than the cooling temperature. With this knowledge, the team found that the lower crust and uppermost mantle “cooled and solidified almost instantly.”
With the findings supporting the Sheeted Sill hypothesis, Dygert and his team are eager to learn more about the Earth’s crust, calling it the “heart of understanding” Earth’s history. The results may have more implications to Earth’s future. More research, however, must be done before confirmation of Dygert’s theory.
By Cheryl Werber
Photo Courtesy Nick Dygert