As most of you are aware, tidal action between the Earth and Moon is both causing the Earth to slow down in its rotation and the Moon to recede from the Earth. Without going into too much detail, the essential culprit is the fact that the Earth's rotation tends to drag the tidal bulge with it, ahead of the line joining the center of the Earth and the Moon. This causes an off-center pull which tranfers angular momentum from the Earth to the Moon. (And because of the Laws of Celestrial Mechanics, pushes the Moon in into a higher, slower orbit.) As you've also likely have heard, this will eventually lead to the the Earth rotating at the same rate as the moon revolves; causing the Earth to always face one side to the Moon. (The tidal effect of the Earth on the Moon has already long ago caused the Moon to be in tidal lock with the Earth.) So far, so good, but what happens then? Is this situation now stable? Actually, no. There is another player on the field; the Sun. And like the Moon has its tidal effects on the Earth, so does the Sun. And as the Earth brought the Moon into tidal lock, the Sun is working on bringing the Earth into tidal lock with the Sun. The result of this is that the Sun will continue to slow the Earth's rotation. As it does so, the Earth will actually start to rotate slower than the moon revolves around it. Again, friction within the Earth's crust will cause the tidal bulge to be out of alignment with the Moon. Only this time, the bulge will lag behind the Moon and tug it backwards rather than forward. This will have the opposite effect of what is happening now, tugging the Moon back into a lower orbit. Lower orbits are faster, and the Moon will also tug on the Earth in an attempt to speed up its rotatation. But the Sun continues to work at slowing the Earth's rotation, and, as a result, the Earth never quite catches up with the Moon, so the Moon will be progressivley be pulled into a lower and lower orbit. This will continue until the Moon passes inside the Earth's Roche limit. At which point, the Moon will break up and form a ring sytem around the Earth. Once this happens, and the Moon's mass is equally distributed around the Earth, there will no longer be any off-center tidal pull and things will finally settle down. The fly in the ointment of all this is the fact that it will take several billion years for it to occur, and our sun will expand into a Red giant long before this, most likely encompassing the Earth and Moon, vaporizing both. (Though I've head of some estimates that have the Red giant only expanding out to the orbit of Venus, so maybe there's a chance, if the Earth-Moon system can survive the blow off of mass and formation of the planetary nebula that marks the end of Red giant stage.) It's a bit of a shame that there may not be enough time for Earth to form such a ring system, it probably would be quite a sight. Consider this, the entire ring system of Saturn is estimated to have a mass of only 1/1000000 of the Moon, and it is spread over a diameter of about 250,000 miles. The Earth's Roche limit is about 16,000 miles, so its ring system would be maybe on the order of 32,000 miles in diameter. A lot more material spread over a smaller distance, making than a lot denser. Granted, Saturn's rings are icey thus more reflective than the rocky ring Earth would have, but the extra amount of material, plus the greater proximity to the sun should make up for this, making the Rings of Earth a sight to behold.