Volcanic activity in 2005 accompanied the formation of a deep, wide rift in Ethiopia on part of the 4,000-mile-long north-to-south trending Great Rift Valley fault. Studies show that the injection of mantle material that “unzipped” the earth along the fault operated the same way as similar material does in less-accessible undersea rifts.

Most diamonds are formed at depths of 150 or so miles. Deep diamonds, however, formed at depths of over 400 miles. The discovery of a new cache of deep diamonds near Eurelia, Southern Australia, has caused some researchers to speculate that they formed much more recently than previously believed.