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.

Sixteen miles from Grand Canyon's south rim, a cone-shaped butte rises like a lone sentinel 1,000 feet above the Coconino Plateau floor. Thousands of tourists rush past on Arizona Highway 64 without giving it another thought, yet this humble little hill testifies to a remarkable past.