Cooling of the Earth

1914

The application of Stefan's law to the calculation of the mean temperature of the earth, at a given latitude, shows that at the latitude of 80 degrees, the temperature was in the neighborhood of 90 degrees Cent., when the sun's radius was about one and a half times its present dimensions, i.e., about two million years ago. Thus it would appear that life commenced on the earth in the vicinity of the poles. The same reasoning leads us to the conclusion that in less than two million years, when the sun's radius will be reduced by one-tenth of its present value, the temperature on the earth will have fallen below 0 degree, even at the equator. — Scientific American.