Do the continents move?
Are there tides in the solid part of the earth as well as in its waters?
The solid Earth is distorted about 4.5 to 14 inches (11.4 to 35.6 centimeters) by the gravitational pull of the sun and moon. It is the same gravitational pull that creates the tides of the waters. When the moon’s gravity pulls water on the side of Earth near to it, it pulls the solid body of the earth on the opposite side away from the water to create bulges on both sides, and causing high tides. These occur every 12.5 hours. Low tides occur in those places from which the water is drained to flow into the two high-tide bulges. The sun causes tides on the earth that are about 33 to 46 percent as high as those due to the moon. During a new moon or a full moon when the sun and moon are in a straight line, the tides of the moon and the sun reinforce each other to make high tides higher; these are called spring tides. At the quarter moons, the sun and moon are out of step (at right angles), the tides are less extreme than usual; these are called neap tides. Smaller bodies of water, such as lakes, have no tides because the whole body of water is raised all at once, along with the land beneath it.
In 1912, a German geologist, Alfred Lothar Wegener (1880–1930), theorized that the continents had drifted or floated apart to their present locations and that once all the continents had been a single land mass near Antarctica called Pangaea (from the Greek word meaning all-earth). Pangaea then broke apart some 200 million years ago into two major continents called Laurasia and Gondwanaland. These two continents continued drifting and separating until the continents evolved into their present shapes and positions. Wegener’s theory was discounted, but it has since been found that the continents do move sideways (not drift) at an estimated 0.75 inch (19 millimeters) annually because of the action of plate tectonics. American geologist William Maurice Ewing (1906–1974) and Harry Hammond Hess (1906–1969) proposed that Earth’s crust is not a solid mass, but composed of eight major and seven minor plates that can move apart, slide by each other, collide, or override each other. Where these plates meet are major areas of mountain-building, earthquakes, and volcanoes.