Earth's Interior — Reading Comprehension

Earth is a dynamic planet with a layered structure that influences everything from earthquakes to the magnetic field that protects us from solar radiation. Scientists have discovered that Earth is not uniform inside, but is divided into different layers that each have unique properties. This layered structure is crucial to understanding how Earth's surface changes and how the planet functions as a system. The study of Earth's interior helps answer questions about why continents move and why we experience natural phenomena like earthquakes and volcanoes.

Layers of the Earth: Structure and Mechanisms
Earth is made up of four main layers: the crust, mantle, outer core, and inner core. The crust is Earth's thin, solid outer shell and comes in two types: oceanic and continental. Oceanic crust is thinner (about 5-10 km thick), denser, and mostly made of basalt rock, while continental crust is thicker (about 30-50 km), less dense, and mostly granite. Beneath the crust lies the mantle, a thick layer (about 2,900 km deep) composed of solid rock that can flow very slowly. The uppermost part of the mantle, combined with the crust, forms the rigid lithosphere, which breaks into tectonic plates. Below the lithosphere is the asthenosphere, a layer where rock behaves plastically and can move. These movements drive convection currents, slowly shifting Earth's plates and causing plate tectonics.

The Core: Source of Earth's Magnetic Field
Beneath the mantle is the outer core, about 2,200 km thick, made mostly of liquid iron and nickel. The movement of this liquid metal generates Earth's magnetic field, which shields life from harmful solar radiation. At the center is the inner core, a solid sphere of iron and nickel with temperatures up to 5,700°C—hotter than the Sun’s surface. The inner core remains solid because it is under intense pressure, despite its extreme temperature. The transfer of heat from the inner core to the mantle drives convection in the mantle, powering plate motion and volcanic activity.

How Do We Know? Seismic Evidence and Scientific Investigation
Scientists cannot directly observe Earth's deep interior, but they learn about it using seismic waves produced by earthquakes. Seismic waves travel at different speeds and directions depending on the materials they pass through. For example, waves speed up in solid, dense layers and slow down or change direction at boundaries between layers. By analyzing these changes, scientists map Earth's interior and estimate the thickness and composition of each layer. Temperature and pressure increase with depth, affecting how materials behave. Understanding these processes helps explain how Earth’s interior heat drives plate tectonics, shaping the continents and ocean basins over millions of years.

Earth’s interior is a complex system where each layer interacts with others to create the planet we know. These interactions control geological processes, influence the environment, and help maintain life on Earth. By studying the Earth’s interior, scientists gain insights not only into our own planet, but also into how other planetary bodies in the solar system might work.

Interesting Fact:
Every year, the continents move a few centimeters—about as fast as your fingernails grow—because of the slow movement of Earth's mantle and tectonic plates.

What are the four main layers of Earth described in the passage?

Which type of crust is thicker and less dense?

What is the main function of Earth's outer core?

What causes tectonic plates to move?

What are seismic waves?

What does the word 'asthenosphere' mean in the passage?

According to the passage, why does the inner core remain solid even though it is extremely hot?

If Earth's magnetic field suddenly disappeared, what would likely happen?

True or False: The mantle is made of completely liquid rock.

True or False: Scientists can directly observe Earth's inner core.