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The length of our Earth day has increased through time. Approximately 900 million years ago, each day was about 18 hours long. By 370 million years ago, the day was 22 hours long. Today, of course, Earth experiences a 24-hour day. The drag of the tides, caused by the gravitational pull of our Moon, slows Earth's rotation. Clementine 1 image showing the circular, ringed Mare Orientale basin, courtesy of NASA and the U.S. Geological Survey. |