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Spreading results when oceanie plates move apart. The ocean floor cracks, magma rises, and new crust is created. Measurements taken at the Mid-Atlantic Ridge show that it spreads a few centimeters (about an inch) every year, pushing Europę and North America farther apart.

Crust

A thin, hard shell of solid rock that forms the Earth’s surface. It is madę up of separate tectonic plates that float on the mantle.

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Outer Core

A layer of molten iron beginning at a depth of 2,900 km (1,800 miles). Scientists monitoring the Earth's magnetic field beiieve it to be caused by the movement of liquid metal in this zonę.

Inner Core

A sphere of solid iron at the center of the Earth.

Mantle

A thick layer of semisolid rock, accounting for 82 percent of the Earth’s volume. The temperaturę inside the mantle reaches 3,700°C (6,692°F). Heat generated below in the Earth’s core causes convection currents in the mantle; rock expands and rises, then slowly sinks again as it cools, causing the movements of the tectonic plates.

Word Link

We can add semi- to some words to refer to something that is half, or partially, complete, e.g., solid— semisolid; circle—semicircle] finał— semi finał] colon—semi colon; annual—semiannual.

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Critical Thinking

Which natural phenomena (e.g., earthquakes, volcanoes) do you think present the greatest challenges to humans?

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