Tectonic Plates — Earth Science Lesson

Reading Passage

What Causes Tectonic Plates to Move?

Earth’s outer shell is divided into large pieces called tectonic plates, which slowly move across the planet’s surface. This movement, just a few centimeters per year, has shaped every continent, mountain range, and ocean basin over billions of years. The engine driving this movement is heat from Earth’s interior.

Deep within Earth, molten rock in the mantle flows in circular patterns called convection currents. Hotter rock near the core rises, spreads, cools, and sinks back down — creating a slow-moving conveyor belt that drags the tectonic plates above it. Where plates move apart, new crust is created at divergent boundaries. Where plates push together, one plate is forced beneath the other in a process called subduction at convergent boundaries.

Tectonic plate interactions create many of Earth’s most dramatic geological features. Convergent boundaries where oceanic plates meet continental plates can build mountain ranges and create volcanic arcs. Divergent boundaries under the ocean form mid-ocean ridges where new seafloor spreads outward. Earthquakes occur along plate boundaries where plates grind against each other.

Scientists believe that all of Earth’s continents were once joined in a single landmass called Pangaea, about 300 million years ago. Evidence for this includes matching fossils found on continents now separated by oceans, and the puzzle-piece fit of coastlines like South America and Africa. Plate tectonics explains how Pangaea broke apart and the continents drifted to their present positions.

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