The rover encounters the San Andreas Fault that rips through the heart of California joining the North American plate to the Pacific plate. What puzzles scientists is why the northern and southern parts lock as the two plates slide past each other, building up strain before catastrophically releasing it to produce powerful quakes while the central part moves steadily, producing smaller ‘creeping’ earthquakes. A new discovery may hold the answer. In September 2007, scientists drilling a borehole through the creeping section of the fault recover over 130 feet (40 meters) of rock core. USGS mineralogist Diane Moore examines the core and discovers talc, a watery mineral of magnesium, silicon and oxygen, within chunks of serpentenite, a crustal rock found at the surface of tectonic plate boundaries. Talc has a layered structure that makes it weak. Moore subjects a sample to high pressures and temperatures of up to 570 degrees Fahrenheit (300 C) to mimic conditions in the fault zone. Moore discovers the talc becomes weaker, leading her to conclude its existence could explain the weakness of the fault and its creeping motion. Scientists are now considering the implications of this for earthquakes worldwide….