Measuring the Earth's Surface (IMAGE) University of Delaware Caption To learn more about plate tectonics, geologists study the outer layer of the earth's surface. Here, University of Delaware researcher Jessica Warren measures the distance between rock samples collected from a peridotite shear zone. Warren and her colleagues performed laboratory experiments on olivine, the main mineral found in the Earth's mantle (the upper ~250 miles of the planet). Olivine also is the main mineral in peridotite rock, which is considered to be a robust model of the interior of the Earth's composition. Credit UNIVERSITY OF DELAWARE Usage Restrictions Must credit UNIVERSITY OF DELAWARE License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.