From: Zardoz ® 04/11/2001 19:38:19 Subject: re: COSMOLOGY FAQ post id: 484074 If the moon was destroyed (by whatever means) would life on Earth be dramatically affected? From: OP (Avatar) If the moon disappeared (*blink*), our first problem would be our orbit about the sun. The earth and moon revolve about a common centre of gravity once a month, and that centre of gravity revolves about the sun once a year, in a elliptical orbit (that is only slightly eccentric.) Actually, I just did some calculations. The speed of our revolution about this centre of gravity. is only about 13 m/s. This would not cause too much trouble. It would move some parts of our orbit by a few tens of thousands of kilometres. Since the Earth-moon system has already cleared a wide swath clean of asteroids etc, we would be very unlucky if this change caused a collision. Certain crustaceans, fish, birds etc would have some migratory and breeding problems. I am not a biological expert, but I gather that even if quite a small percentage of species are made extinct directly by an event, there can be knock-on effects throughout the ecosystem causing a number of secondary extinctions. There would still be two tides a day, caused by the sun. They would be about a quarter of the magnitude of our current tides, and much more regular in size. This would obviously have a deleterious effect on plants and animals in the tidal zone. This zone would still exist, but it would be much narrower. No matter what the scale of the extinction event, we can pretty much count on life surviving. The moon causes a tidal bulge, which (judging by the "lag" in the earth tides) would take hours to die down. The moon causes a flex in the earth's asthenosphere, which is constantly changing in orientation, and causing minor changes in stress. In the moon's absence, these would disappear after a very short time (the long period oscillations are heavily damped), leaving us with the Sun's tidesm which would continue to flex the asthenosphere, but to a much lesser extent. The stresses and rates of change in stress would all be lower than they are now. In short, there would be less tidal influence on volcanism and tectonism. Nothing would happen to the earth's axis, except that the slow precession (which has a 25000 year cycle) would occur at a much reduced rate. This would have no deleterious effects, and would mean star atlases don't have to be updated quite so often.