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From the deepest ocean trench to the tallest mountain, plate tectonics explains the features and movement of Earth’s surface in the present and the past. Plate tectonics is the theory that Earth’s outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core. The plates act like a hard and rigid shell compared to Earth’s mantle. This strong outer layer is called the lithosphere. The rising of hot rock from the mantle to Earth’s surface is called upwelling. This process adds new material to tectonic plates. Over time, the cooling outer crust becomes thicker and heavier. After millions of years, the oldest, coolest parts of the plate sink back into the mantle, where they remelt again. This text presents a major breakthrough in our understanding of the subject of plate tectonics, invaluable to students in the earth sciences and to various specialists in the geological sciences.
