In addition, the changing weight of the oceans and atmosphere can cause deformations of the crust "on the order of a centimeter or so," notes geophysicist Richard Gross at the Jet Propulsion Laboratory in Pasadena, Calif. And the gravitational pull of the moon and sun not only cause ocean and atmospheric tides but earth tides as well. Mountains and valleys emerge and disappear due to plate tectonics. Mass shifts around inside the planet, altering those gravitational anomalies.
The greater a concentration of mass is, the stronger its gravitational pull, "creating bumps around the globe," says geologist Joe Meert at the University of Florida in Gainesville.Įarth's shape also changes over time due to a menagerie of other dynamic factors. Our globe, however, is not even a perfect oblate spheroid, because mass is distributed unevenly within the planet. The effect would be similar to spinning a bit of Silly Putty, though Earth's plasticity is much, much less than that of the silicone plastic clay so familiar to children." Instead of Earth being like a spinning top made of steel, explains geologist Vic Baker at the University of Arizona in Tucson it has "a bit of plasticity that allows the shape to deform very slightly. He was correct and, because of this bulge, the distance from Earth's center to sea level is roughly 21 kilometers (13 miles) greater at the equator than at the poles. Instead, he suggested it was an oblate spheroid-a sphere that is squashed at its poles and swollen at the equator. Isaac Newton first proposed that Earth was not perfectly round. This was based on a number of observations, such as the fact that departing ships not only appeared smaller as they sailed away but also seemed to sink into the horizon, as one might expect if sailing across a ball says geographer Bill Carstensen of Virginia Tech in Blacksburg. Well before Columbus sailed the ocean blue, Aristotle and other ancient Greek scholars proposed that Earth was round. Planet Earth is not, in fact, perfectly round. As countless photos from space can attest, Earth is round-the "Blue Marble," as astronauts have affectionately dubbed it.
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