Earth’s Structure — Reading Comprehension Lesson

Reading Passage

Earth’s Structure

If you could cut Earth in half like an apple, you would see that it is made of several different layers. Scientists have learned about Earth’s interior by studying the way earthquake waves travel through the planet. Each layer has different properties — including different temperatures, pressures, and types of rock or metal.

The outermost layer is the crust. The crust is the thinnest layer, averaging about 30 kilometers thick under the continents and just 5 to 10 kilometers thick under the ocean floors. The crust is made mostly of solid rock and is the layer where all living things are found. Below the oceans, the crust is made of denser rock than under the continents.

Below the crust is the mantle, which makes up the largest part of Earth’s interior. The mantle is about 2,900 kilometers thick and is made of rock that is very hot. Although the rock in the mantle is solid, it can flow very slowly — like thick putty — over millions of years. This slow movement of rock in the mantle is what drives the movement of tectonic plates.

Below the mantle is Earth’s core. The core is divided into two parts: the outer core and the inner core. The outer core is made of liquid iron and nickel and is about 2,200 kilometers thick. As this liquid metal moves, it creates electric currents that generate Earth’s magnetic field, which protects the planet from harmful solar radiation.

At the very center of Earth is the inner core — a solid ball of iron and nickel about 1,200 kilometers in radius. Even though temperatures in the inner core can reach over 5,000 degrees Celsius, the extreme pressure from all the layers above keeps the metal solid. The inner core is the hottest and densest part of Earth.

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