The cycles that Milankovitch proposed are much more clearly evident on Mars than on Earth. This is because Mars is closer to the outer giant planets and has no large moon. Consequently, its orbital eccentricity varies from 0.00 (circular orbit) to 0.13—more than twice that of Earth—over the course of 95,000-99,000 years. Obliquity changes even more dramatically, from about 13° to 47°, over 120,000 years. The Martian equinoxes also pre-cess, returning to an initial position over a period of about 51,000 years. These cycles coincide with major climate changes on Mars, measured as the rate at which ice forms and vaporizes around the Martian North Pole.
Milutin Milankovitch devoted his entire professional life to elucidating this link between the Earth's rotation and orbit and major climate changes. It was a formidable task—performed before there were even pocket calculators, far less computers, to help with the math! His theory could not be confirmed in his own lifetime, and even now we cannot say that it is proven beyond all possible doubt. Nevertheless, there is a considerable body of evidence to support it and scientists are beginning to understand how the link works. It shows that the climates of Earth and Mars change for entirely natural reasons due to forces outside the planets themselves.
Louis Agassiz and the Great Ice Age
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