Astronomers and geologists and those who study physics have been able to tell us something of the origin and history of the earth. They consider that, vast ages ago, the sun was a spinning, flaring mass of matter, not yet concentrated into a compact centre of heat and light, considerably larger than it is now, and spinning very much faster, and that as it whirled, a series of fragments detached themselves from it, which became the planets. Our earth is one of these planets. The flaring mass that was the material of the earth broke as it spun into two masses, a larger, the earth itself, and a smaller, which is now the dead, still moon. Astronomers give us convincing reasons for supposing that sun and earth and moon and all that system were then whirling about at a speed much greater than the speed at which they are moving to-day, and that at first our earth was a flaming thing upon which no life could live. The way in which they have reached these conclusions is by a very beautiful and interesting series of observations and reasoning, too long and elaborate for us to deal with here. But they oblige us to believe that the sun, incandescent though it is, is now much cooler than it was, and that it spins more slowly now than it did, and that it continues to cool and slow down. And they also show that the rate at which the earth spins is diminishing and continues to diminish--that is to say, that our day is growing longer and longer, and that the heat at the centre of the earth wastes slowly. There was a time when the day was not a half and not a third of what it is to-day; when a blazing hot sun, much greater than it is now, must have moved visibly--had there been an eye to mark it--from its rise to its setting across the skies. There will be a time when the day will be as long as a year is now, and the cooling sun, shorn of its beams, will hang motionless in the heavens. It must have been in days of a much hotter sun, a far swifter day and night, high tides, great heat, tremendous storms and earthquakes, that life, of which we are a part, began upon the world. The moon also was nearer and brighter in those days and had a changing face.[3] II THE RECORD OF THE ROCKS § 1. _The First Living Things._ § 2. _How Old Is the World?_ § 1 We do not know how life began upon the earth.[4] Biologists, that is to say, students of life, have made guesses about these beginnings, but we will not discuss them here. Let us only note that they all agree that life began where the tides of those swift days spread and receded over the steaming beaches of mud and sand.