Crystals of magnesiowüstite, a common mineral within the deep earth, can transmit infrared radiation at normal atmospheric pressures (inset, top), but when squashed to over a half million times the pressure at sea level, they lose this ability (inset, bottom). The arrow shows the region near the core-mantle boundary where magnesiowüstite is found. (Inset images used with permission of the American Association for the Advancement of Science, Science, May 26, 2006 issue; background image courtesy NASA and the Johns Hopkins Applied Physics Laboratory. Click image for high resolution version.)