Using a new imaging tool—electrical resistivity tomography (ERT)—two geophysicists investigate an area that they suspect was a burial pit in Lithuania during the Holocaust, in this excerpt from NOVA: Holocaust Escape Tunnel. Using hundreds of electrical impulses to measure how soil conducts electricity, ERT scans the ground and creates a map that identifies disturbances in the soil—without disrupting the ground. These changes in the soil would indicate activity, such as a mass grave. Archeologists were able to confirm the location of a site where thousands of people, mostly Jews, were killed and buried by the Nazis. This resource is part of the NOVA Collection.