Tidal Friction

from, The Sea Around Us by Rachel L. Carson:

In the days when the earth was young, the coming in of the tide must have been a stupendous event. If the moon was...formed by the tearing away of a part of the outer crust of the earth, it must have remained for a time very close to its parent. Its present position is the consequence of being pushed farther and farther away from the earth for some 2 billion years.

...[O]ver the millions of years the moon has receded, driven away by the friction of the tide it creates. ...[F]or tidal friction is gradually slowing down the rotation of the earth. In those early days..., it took the earth a much shorter time--perhaps only about 4 hours--to make a complete rotation on its axis. Since then, the spinning of the globe has been so greatly slowed that a rotation now requires, as everyone knows, about 24 hours.

...And all the while the tidal friction will be exerting a second effect, pushing the moon farther away... (According to the laws of mechanics, as the rotation of the earth is retarded, that of the moon must be accelerated, and centrifugal force will carry it farther away.) As the moon recedes, it will, of course, have less power over the tides and they will grow weaker. It will also take the moon longer to complete its orbit around the earth.

...Our day is believed to be several seconds longer than that of Babylonian times. Britain's Astronomer Royal recently called the attention of the American Philosophical Society to the fact that the world will soon have to choose between two kinds of time. (1950)