By studying sediment layers in the Tarim Basin, shown above, geologists have determined that the Taklimakan Desert in northwest China is at least 5.3 million years old. The light yellow strata are composed of wind-blown silt from the desert's formation, embedded in older, darker rock. The Taklimakan is the second largest sand dune desert in the world, after the Empty Quarter of the Arabian Peninsula. Scientists theorize that the desert was created by climate change caused by shifting ocean currents and the uplift of the Tibetan Plateau. The work is detailed in the June 16 issue of Science.