Dictionary of Human Evolution and Biology

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Tidal Cycles

Rhythmic minima and maxima of tides caused by three gravitational phenomena: perigee of the moon (i.e. when it is nearest to the earth; every 411 days), the perigee of the earth (when it is nearest to the sun), and the alignment of the earth, moon and sun that causes a lunar eclipse. These three events are synchronous approximately once every 1.8 kya; it has been suggested that this synchronicity could cause powerful tides that may cause deep cooling in the Atlantic, and trigger global cooling, including the Little Ice Age 500 years ago.

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