"Like Earth, Mars has a precessional wobble. While it takes Earth about 25,800 years to complete one precessional loop, it takes Mars about twice that long. The astronomer Carl Sagan has suggested that Mars may now be in the grips of precessional winter, with an extensive polar ice cap in the Northern Hemisphere containing the bulk of the planet's potential atmospheric mass. If so, then 25,000 years ago the planet would also have been in the grip of precessional winter, but this time with the bulk of the atmosphere locked up in the Southern Hemisphere ice cap. But 12,000 year ago the planet would have been enjoying precessional spring and summer, "a time on Mars of balmy temperatures, soft nights, and the trickle of liquid water down innumerable streams and rivulets, rushing out to join mightily gushing rivers," according to Sagan. "if so," he goes on, "twelve thousand years ago was a good time on Mars for life similar to the terrestrial sort. If I were an organism on Mars, I might gear my activites to the precessional summers and close up shop in the precessional winters--as many organisms do on Earth for our much shorter annual winters. I would make spores; I would make vegetative forms; I would go into cryptobiotic repose; I would hibernate until the long winter had subsided.""
A third way in which Earth's attitude in space changes with respect to the Sun, and so can bring about climate change, is its varying mean distance from the Sun, called its eccentricity. Earth's eccentricity varies from zero to a value of about 0.06 once every 93,000 years. When at its greatest eccentricity and most distant from t he Sun, Earth receives an estimated 20 percent less solar radiation than when we are closest to the Sun. From the standpoint of climate change, this is a significant amount when you consier that a drop by only 13 percent would bring on a super ice age, covering Earth's entire surface with a blanket of ice 1.6 kilometers (one mile) thick. A rise of 30 percent would bring on a heat wave that would destroy virtually all Earth life.
Three scientists working on Project Climap, which analyzed hundreds of ocean bottom cores taken from the Southern Hemisphere, have come to the conclusion that changes in Earth's orbit have been the basic cause of the advancing and retreating of ice over the past two million years. The scientists are a Columbia University geologist, J.D. Hays; a Brown University oceanographer, John Imbrie; and a Cambridge University Quaternary Research Specialist, N.J. Shackleton. Their ocean-floor cores contain climate records of the past 450,000 years. They claim to have found peaks of climate change occurring regularly at 23,000-year periods, which would tend to fit the 25,800-year of precessional wobbles. Another series of climatic peaking occurs every 42,000 years, which would tend to fit the 41,000-year cycle of obliquity shifting. And a third series of climatic peaks occurs about every 100,000 years, which tends to fit the cycle of eccentricity change. Recall Bryson saying that the time between peaks of ice periods was about 100,000 years.
Gallant 1979:152-153 A third way in which Earth's attitude in space changes with respect to the Sun, and so can bring about climate change, is its varying mean distance from the Sun, called its eccentricity. Earth's eccentricity varies from zero to a value of about 0.06 once every 93,000 years. When at its greatest eccentricity and most distant from t he Sun, Earth receives an estimated 20 percent less solar radiation than when we are closest to the Sun. From the standpoint of climate change, this is a significant amount when you consier that a drop by only 13 percent would bring on a super ice age, covering Earth's entire surface with a blanket of ice 1.6 kilometers (one mile) thick. A rise of 30 percent would bring on a heat wave that would destroy virtually all Earth life.
Three scientists working on Project Climap, which analyzed hundreds of ocean bottom cores taken from the Southern Hemisphere, have come to the conclusion that changes in Earth's orbit have been the basic cause of the advancing and retreating of ice over the past two million years. The scientists are a Columbia University geologist, J.D. Hays; a Brown University oceanographer, John Imbrie; and a Cambridge University Quaternary Research Specialist, N.J. Shackleton. Their ocean-floor cores contain climate records of the past 450,000 years. They claim to have found peaks of climate change occurring regularly at 23,000-year periods, which would tend to fit the 25,800-year of precessional wobbles. Another series of climatic peaking occurs every 42,000 years, which would tend to fit the 41,000-year cycle of obliquity shifting. And a third series of climatic peaks occurs about every 100,000 years, which tends to fit the cycle of eccentricity change. Recall Bryson saying that the time between peaks of ice periods was about 100,000 years.