Underwater image of live coral Montastraea annularis. Note polyp tissue (green) around the mouth and base of the tentacles and zooxanthellae (red fluorescence from chlorophyll) in the tissue between polyps. Tentacles also are visible.
Richat Structure: A geological formation in the Maur Adrar Desert in Mauritania, Africa. Although it resembles an impact crater, the Richat Structure formed when a volcanic dome hardened and gradually eroded, exposing the onion-like layers of rock