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Early in Solar System history, the Earth rotated on its axis at a much faster rate than it does today and the Moon circled the Earth more rapidly as well. Days then were only several hours long, and the month lasted only tens of hours. The tides that the Moon raises on the Earth act back on the Moon and slowly push it away lengthening the month. This effect also slows down the spinning Earth, and so the day lengthens over time. These effects are ongoing: the Moon is receding from Earth at a rate of about a centimeter annually, and the Earth's spin continues to slow in response. To learn more click here.
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