Timmy McCourt, age 12, of Ottawa, Ontario, Canada, for his question:
Has the North Pole always been in the same place?
An orbiting satellite, way out in space, could provide an answer to this question. The geography of the earth's surface provides a whole series of different answers. The satellite answer reveals that the North Pole swings around, pointing to different celestial objects in outer space. The surface planetary evidence reveals that the North Pole appears to wander around on global tours. What's more, it also has other motions.
We know now that the North and South Poles once occupied other continents and seas. New evidence keeps arriving to prove that they have been wandering on global tours for millions of years. They are creeping around right now and doubtless will continue. Or so it seems. Actually, these geographical tours are motions of the earth's crust. This surface skin of our solid planet is the rocky layer of rocks that forms the continents and supports the sea beds. It fits rather like a loose packet on top of the thick, dense mantle layer below.
Gravity and other forces are exerted on the loosely fitting crust, both from within the earth and from outer space. Hence, the crust is in a state of constant unrest. Its geographical history is an endless story of remodeling mountains, oceans and continents. A few decades ago, scientists proved that the North and South Poles even wander around the map. They are, of course, the opposite ends of the earth's axis. But, they continue to point to the same regions of the sky during their grand global tours. Obviously, they do not change the angle of the axis so the crustal geography of land and sea must glide around the globe.
About 300 million years ago, the North Pole was located near Hawaii, and 150 million years later it was near Japan. During the past 50 million years, the slithering crust has shifted the North Pole from Siberia to its present location under the Arctic Sea. Meantime, at the opposite end of the axis line, the South Pole has been shifted through matching global migrations.
Apparently, these polar tours are not related to changes in the angle of the axis. But the axis does perform slight swaying patterns. As this happens, the North Pole's pointing finger sketches circles in the sky. An axis motion, called precession, resembles a spinning top wobbling to a stop. Each precession circle takes 26,000 years and during this time the North Pole points around a series of different Pole Stars. Meantime, other miniscule changes in the axis shift to match the changing positions of the sun, moon and even the planets.
All these polar motions are governed by gravity, magnetism and other stupendous cosmic forces. The polar tours depend mostly on earth forces exerted on the loose crust. Precession and other motions depend mostly on forces exerted by celestial neighbors the sun, moon and even other planets. It may be misleading to compare precession to a weary top. Actually, the forces that govern it never tire and our peppy old planet is not planning to spin slower and tip over.