This afternoon at 3:02, the Sun will cross the equator initiating the autumnal equinox. Before the designation of seasons some cultures recognized the seasons as either rainy or dry. Others have recognized three seasons: growing, harvesting and winter, while others have marked ten or more seasons. The designation of four seasons has a beginning and end point. They are defined when the Earth moves around the Sun. The word equinox comes from the Latin for "equal night." This isn't the case at the exact moment of the autumnal equinox for two reasons: Sunrise and sunset occurs when the Sun's top edge crosses the horizon.  Earth's atmosphere changes the Sun's apparent position when the Sun is lowThe Journal of Geophysical Research-Solid Earth reports that the North American continent is kept afloat by heat that makes rocks buoyant.  Comparing the continent to a rock, one theory depicts that if the temperature of the continent cooled to 750 degrees, it would sink. That is the temperature of some of the coldest crust rock in North America and researchers believe that this cooling would sink New York into the Atlantic by 1,427 feet.  Los Angeles would dip 3,756 feet under the Pacific and Denver, would be 727 feet under water. The immediate benefit is this cooling process would take billions of years. Seattle will actually rise because it is positioned on a cold rock slab.