Earth: Layer by Layer
What are the four main layers of Earth, starting from the center?
How do scientists learn about the inside of Earth if they cannot go there?
What is the inner core made of?
How hot is the inner core compared to the sun?
What is special about the outer core?
What is the mantle like?
What is the asthenosphere?
How are diamonds formed and brought to the surface?
What are tectonic plates?
What happens when tectonic plates move?
Discovering What’s Beneath Our Feet
When we look at Earth, we see tall mountains, deep oceans, and wide valleys. The surface of our planet is an amazing place, full of different landforms and wonders.
But if you could dig straight down, you would discover that what we see on the outside is just a thin shell.
To really understand our planet, we need to learn about the layers that make up Earth, all the way to its very center, which is almost 4,000 miles (6,400 kilometers) below our feet.
The Four Main Layers of Earth
Earth is made up of four main layers.
Starting from the very center and moving outward, these layers are called the inner core, the outer core, the mantle, and the crust. Only the crust is close enough for people to study directly. In fact, the deepest hole ever drilled by humans is just over 7.6 miles (12 kilometers) deep, which is barely a scratch on the surface compared to the size of the whole planet.
Even though we can’t visit the deeper layers, scientists have learned a lot about them by studying how earthquake waves move through Earth. These waves travel at different speeds depending on what kind of material they pass through. Scientists have also used math and physics to figure out what’s inside Earth by looking at things like gravity and the planet’s magnetic field.
The Inner Core
At the very center of Earth is the inner core. This is a solid ball made mostly of iron and nickel, and it is about three-quarters the size of the moon.
The inner core is found about 4,000 miles (6,400 kilometers) below the surface. It is extremely hot, with temperatures reaching around 9,800 degrees Fahrenheit (5,400 degrees Celsius)—almost as hot as the surface of the sun!
The pressure here is also huge, more than three million times greater than what we feel on the surface. The inner core spins a little faster than the rest of the planet. Some scientists even think there could be an “inner, inner core” made almost completely of iron.
The Outer Core
Surrounding the inner core is the outer core. This layer is also made of iron and nickel, but here, these metals are melted and form a hot, swirling liquid.
The outer core stretches from about 3,220 miles (5,180 kilometers) to 1,790 miles (2,880 kilometers) below the surface. The liquid iron and nickel move in big, churning currents, which create electrical currents.
These electrical currents are what make Earth’s magnetic field.
The magnetic field helps protect us from harmful rays from space and even helps some animals know which way to go when they migrate. Every 200,000 to 300,000 years, Earth’s magnetic field actually flips, with the north and south poles switching places, but scientists are still trying to understand exactly why this happens.
The Mantle
Above the outer core is the mantle, which is the thickest layer of Earth. The mantle is about 1,865 miles (3,000 kilometers) thick. It starts just 18.6 miles (30 kilometers) below the surface.
The mantle is made of heavy materials like iron, magnesium, and silicon. It is very hot and is not completely solid—it is more like thick, sticky caramel. The mantle moves, but very slowly.
Near the top of the mantle, between about 62 and 124 miles (100 to 200 kilometers) underground, the temperature is so high that some of the rock melts. This melted area is called the asthenosphere. The asthenosphere is soft and slippery, and it is what the huge pieces of Earth’s crust, called tectonic plates, move on.
Diamonds, which are rare and beautiful crystals, are actually tiny pieces of the mantle that have made their way to the surface. Most diamonds form more than 124 miles (200 kilometers) below ground, but some “super-deep” diamonds may have formed as far down as 435 miles (700 kilometers) below the surface. These diamonds are brought up by special volcanic rocks called kimberlite.
The very top part of the mantle is cooler and harder than the rest. It acts more like the crust above it. Together, the uppermost mantle and the crust form what scientists call the lithosphere.
The Crust
The crust is the outermost layer of Earth.
It is very thin and brittle compared to the layers below. The crust is made mostly of light materials like silica, aluminum, and oxygen. The thickness of the crust changes depending on where you are.
Under the oceans, the crust can be as thin as 3.1 miles (5 kilometers). Under big mountain ranges, like the Himalayas, it can be up to 43 miles (70 kilometers) thick.
The crust, along with the top part of the mantle, is broken into large pieces called tectonic plates. These plates fit together like a giant jigsaw puzzle.
They move very slowly—only about 1.2 to 2 inches (3 to 5 centimeters) per year. Scientists are still learning exactly what makes these plates move. It might be the heat and movement in the mantle below, or it could be because of the way denser plates pull on lighter ones, a process called “slab pull.”
When plates move, they can bump into each other, pull apart, or slide past one another. These movements cause earthquakes and volcanoes. Even though the plates move slowly, they shape the surface of our planet and create exciting changes over time.
Why Earth’s Layers Matter
Understanding Earth’s layers helps us know how our planet works. The movement of the plates shapes the land, creates mountains, and causes earthquakes and volcanoes.
The magnetic field made by the outer core protects life on Earth. Even the diamonds we find in jewelry are clues about what happens deep inside the planet. By studying Earth’s layers, scientists can learn more about how our planet formed, how it changes, and what might happen in the future.
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► COMPREHENSION QUESTIONS
— please answer with complete sentences
What are the four main layers of Earth, starting from the center?
How do scientists learn about the inside of Earth if they cannot go there?
What is the inner core made of?
How hot is the inner core compared to the sun?
What is special about the outer core?
What is the mantle like?
What is the asthenosphere?
How are diamonds formed and brought to the surface?
What are tectonic plates?
What happens when tectonic plates move?
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