Afar Depression, Ethiopia: Image of the Day

In eastern Africa, in the Afar region of Ethiopia, a nearly barren rockscape marks the location of the meeting place of three separate pieces of the Earth's crust. This meeting place is known to geologists as the Afar Triple Junction; the central meeting place for the three pieces of Earth's crust is around Lake Abbe, just to the south of the area shown in this image from the Advanced Spaceborne Thermal Emission and Reflection Radiometer asterweb.jpl.nasa.gov (ASTER) on NASA's terra.nasa.gov Terra satellite. The three pieces of Earth's crust are each pulling away from that central point, though not all at the same speed. The pulling apart creates enormous stress on the rock, producing cracks, faults, volcanoes, fumaroles (gas vents), escarpments, and hot springs in the region along the border of Ethiopia, Eritrea, and Djibouti. In this image, the gray-brown, ancient, basalt rock of the region is crisscrossed by cracks both small and large, many of which are filled with salt and sand, though in this infrared-enhanced satellite image, the tinge of red indicates some hardy vegetation eking out a living in the harsh terrain. The large river-like feature running horizontally across the scene is actually a geologic feature called a ''graben,'' a gulley created not by erosion of a river but by the sinking of the ground when earth on either side pulls apart. Besides its unusual geology, the Afar region is famous for its fossils. On November 24, 1974, a team of American paleoanthropologists led by Donald Johanson discovered a fossil hominid of a young adult female only a meter tall. While the team examined the find, the Beatles song Lucy in the Sky with Diamonds played on the radio, and the team decided unanimously to call the fossil ''Lucy.'' Years later, she got her formal scientific designation: Australopithecus afarensis. Radiometric dating of underlying volcanic rocks placed Lucy's age at 3.2 million years old.