Earth's insides can be broken down into different layers. The way it's broken down depends on what criteria* you use. You can break it down based on materials. This is called compositional layers. You can break it down based on how strong or rigid the material is. This is called mechanical layers.
*a standard or test used to judge or decideRemember that compositional layers are broken down based on what they're made of.
The crust is the outside layer of Earth. It is like the skin of an apple or the shell of a hard boiled egg. It can be broken down into two different parts: continental crust and oceanic crust.
Continental crust is found under continents. It is mostly made of granite rock. While the thickness of the continental crust varies, it averages 40 km (25 miles) thick.
Oceanic crust is found under the oceans. It is mostly made of basalt rock. The thickness of oceanic crust varies, but it is an average of 6 km (4 miles) thick.
The mantle sits under the crust. It is kind of like the yummy part of an apple or the white part of a hard boiled egg. The mantle can be divided into the upper and lower mantle. The upper mantle is cooler and less dense because it is farther from the core.
The mantle is solid. While it is solid, it is ductile or plastic. Plasticity is the quality of being able to be molded. Think about silly putty. It is solid, but you can change its shape. Because it is plastic, or has plasticity, it can flow over a very long time with a lot of pressure.
The mantle is mainly made of silicate rocks rich in iron and magnesium. The mantle is approximately 2,900 km (1,802 miles) thick, making it the largest compositional layer of the earth. Temperatures in the mantle average 3000℃ (approximately 5432 degrees Fahrenheit).
The core is at the center of Earth. You can think of it as the core of an apple, or, more accurately, the yolk of an egg. The core is made mostly of iron and nickel. It can actually be split into two layers! The liquid outer core swirls around the solid inner core. Scientists theorize that the motion of the liquid outer core around the solid inner core causes the magnetic field around Earth.
The outer core lies beneath the mantle. The outer core is the only liquid layer of Earth. Like the inner core, it is made of mainly iron and nickel. We infer that it is liquid because something around the center of Earth blocks certain types of seismic waves (earthquake vibrations) from reaching the other side of Earth. Temperatures in the outer core are about 4000-5000℃ (7232-9032 degrees Fahrenheit). The outer core is about 2,300 km thick (1429 miles).
The inner core is surrounded by the outer core. Like the outer core, it is mostly made of iron and nickel. The inner core, however, is solid. This is because of the tremendous pressure of the material above it. The temperature in the inner core is 5000-6000℃ (9032-10832 degrees Fahrenheit). This is hotter than the surface of the sun! The inner core is 1,250 km thick (777 miles). It rotates faster than the rest of the Earth.
Recall that mechanical layers are divided based on how strong or rigid the material is.
The lithosphere is the outside mechanical layer of the earth. It is made of rigid rock. It includes the crust and the top of the mantle. The word lithosphere is from Greek litho (stone) and sphere. The lithosphere extends about 70-100 km (43-62 miles) below the surface.
The asthenosphere sits below the lithosphere. This is a solid yet plastic layer. Remember that plasticity is the ability to be molded. The asthenosphere is about 100-350 km (62-217 miles) thick. It is found in the upper mantle. Asthenosphere comes from Greek asthenia (weak) and sphere. Materials in the asthenosphere flow and carry pieces of the lithosphere with them.
The mesosphere is beneath the asthenosphere. Mesosphere comes from Greek mesos (middle) and sphere. The mesosphere flows, but at a slower rate than the mantle. It extends from the asthenosphere down to the outer core.
We have not been able to drill all the way through the crust, so how do we know what is inside the Earth?
Scientists study seismic waves to learn about the interior of Earth. Seismic waves are vibrations released by earthquakes. The seismic waves travel from the source of the earthquake, or focus, in every direction. When an earthquake occurs, scientists measure the seismic wave using devices called seismographs. There are seismograph stations all over the world. There are different types of seismic waves. Some types of seismic waves can travel through both solid and liquid materials. Other seismic waves cannot travel through liquids. By studying the seismic waves released by earthquakes, scientists can infer what the inside of Earth is like.