Since the problem of the origin of the earth is an essential part of the problem of the origin of the solar system, the following well-known facts should be clearly in the mind of the reader. Eight planets, including the earth, revolve in nearly circular paths around the central sun, whose diameter is 866,000 miles. The radius of the solar system is at least 2,800,000,000 miles, this being the distance of the outermost known planet (Neptune) from the Sun. Neptune requires 164 years for a trip around the sun, while the earth, which averages about 93,000,000 miles from the sun, makes its circuit once a year. The planets all revolve around the sun in the same direction, and in nearly the same plane. The sun and all eight planets rotate on their axes in the same direction, the earth's rotation being accomplished every twenty-four hours. Most of the planets have one or more smaller bodies called satellites revolving about them, such as Earth, with its one satellite (the moon), and Saturn, with its eight satellites, etc. It is well known that this solar system is only a very small part of the vast universe, as shown by the facts that no star is nearer the earth than several trillion miles, and that some stars are so far away that light traveling at the rate of 186,000 miles per second requires a thousand years to reach the earth! Toward the end of the eighteenth century the famous nebular or ring hypothesis was set forth by the astronomer named Laplace. This assumes an original very hot incandescent mass of gas spheroidal in shape and greater in diameter than the present solar system. This mass rotated in the direction of rotation of our sun and its planets. Loss of heat by radiation caused the mass to shrink, and this in turn not only made it rotate faster, but also caused the centrifugal force (i.e., the force whose direction was from the center) in its equatorial portion to gradually become stronger. Finally a time came when the force of gravity (i.e., the force whose direction was toward the center) and the centrifugal force became equal and a ring was left (not thrown) off, while the rest of the mass of gas continued to shrink. After a time the material of the ring collected to form the outermost planet. The other planets were similarly formed from other rings which were left off as contraction of the great mass of gas went on. The sun represents the remainder of the great mass of rotating gas.