Plate tectonics — Geography, 14–17 years
Earth’s outer rocky shell is divided into moving plates whose interactions shape continents, mountains, volcanoes and earthquakes.
A moving rocky shell
Earth’s lithosphere, the strong outer layer, is broken into large plates. They move only a few centimetres each year over hotter, softer rock below. Where plates pull apart, collide or slide past one another, they create many of the features and hazards found at Earth’s surface.
Why scientists needed this idea
Earthquakes, volcanoes, deep ocean ridges and mountain chains once seemed like unrelated facts. The fit of some continental coastlines and matching fossils suggested that continents had moved, but an explanation was missing. Plate tectonics connected these clues: slow movements of plates can produce sudden events and reshape Earth over millions of years.
The Atlantic getting wider
At the Mid-Atlantic Ridge, plates move apart and new ocean crust forms. Suppose the average spreading rate is 2.5 cm per year. In 1,000,000 years, 2.5 cm × 1,000,000 = 2,500,000 cm; dividing by 100,000 gives 25 km. This simple calculation shows how a tiny yearly movement becomes a large change over geological time.
The plates do not move like loose puzzle pieces
A diagram can make plates look like separate pieces floating freely on liquid. That is a reasonable impression, but plates are thick, solid parts of the lithosphere, and the rock beneath is not an underground ocean. Heat inside Earth helps drive slow circulation and other forces; friction can lock plate edges until stress is released in an earthquake.
Living with moving plates
Plate boundaries help planners identify areas more likely to face earthquakes, volcanic eruptions or tsunamis. Engineers can design buildings, bridges and warning systems with those hazards in mind. Geologists also use plate movements to understand where some ores, geothermal energy and new crust may be found.
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