14 June 2013
Vol 340, Issue 6138

About The Cover

Cover image expansion

COVER Polished thin section (70 micrometers) of volcanic glass, sample catalog number NMNH115296-3, in transmitted light (14 by 18 millimeters). Molten lava erupted onto the sea floor freezes to glass and minerals that contain clues to the lava's ancient past and origin in Earth's deep interior. Volcanic glasses such as this one may reveal a link between Earth's oxidation state and the deep carbon cycle. See page 1314. Image: G. Macpherson, T. Gooding, and E. Cottrell