All water on the Earth stays in continuous movement. The solar energy falling on the Earth, actuates two mechanism closely connected among themselves - movement of atmosphere and movement of water. The uneven variable heating of a terrestrial surface by the Sun moves air. Being heated up in an equatorial zone, it emerges and moves to poles, there it is cooled, is lowered and comes back in an equatorial zone. Rotation of the Earth, uneven distribution of continents and oceans on its surface and many other factors transform this simple movement into complex system of constant circulation of terrestrial atmosphere.
Moisture movement, connected with it, is also very complicated. Moisture continuously evaporates from heated surfaces of land and sea. It sates an atmosphere with the water ferry, forms clouds and is transferred together with atmospheric flows. Each year about 450 thousand, and from a surface of land about 70 thousand cubic kilometres of water evaporates from a surface of ocean. It drops out with deposits: about 420 thousand on ocean, about 100 thousand cubic kilometres on land. It is obvious, that the land receives about 30 thousand cubic kilometres of water, evaporated from the surface of the oceans.
The science does not know precisely what can explain the occurrence and ending of glacier periods. Maybe, the amount of solar energy getting on a terrestrial surface, has changed, or the properties of an atmosphere, for example its contamination by a volcanic dust have changed, and it has begun to pass thermal radiation differently. And by the way,can there be other climates on the Earth at the same arrangement of continents and oceans, at the same receipt of energy from the Sun? Also maybe, the climate changes, when the deviation of atmospheric and oceanic processes will exceed some level? There are no convincing answers to these questions for the present.
That is the way the movement of moisture was done during the centuries - one of parts of the planetary machine and one of most ancient (after gravitation) mechanisms of the Earth. But recently man more and more interferes its course.
