The Earth’s Interior

We live on Earth’s surface, but what exactly is below us? Below the Earth’s surface is the interior. Think of it as a hard boiled egg. If you tear open the egg you will see layers. There is the shell (the crust of Earth), the egg white (Earth’s mantle), and the yolk (Earth’s core). Crust Shell Mantle White Core Yolk

Or, you could think of it as an apple.

Now, what about these layers of the Earth…. Earth is made up of three layers. They are: crust, mantle, and core. Each layer has a different temperature, composition and density. The temperature and density increase with depth.

Earth’s Crust The crust is the outer layer of Earth. It is made up of solid rock and it is the thinnest of the three layers. The crust is between 5km to 50km (3 to 31 miles) thick and it makes up less than one percent of Earth’s mass. There are two types of crust: continental and oceanic crust. Continental crust is the lighter older, and thicker part of the crust that makes up the continents. Oceanic crust is the rock that forms the ocean floor. It is made of denser rock than continental crust. The temperature of both kinds of crust increases with depth. Where the crust meets the mantle, temperatures can reach 400°C (about 750°F). That is hot!! But the closer we get to the core, the hotter it gets!!

Earth’s Mantle The mantle is the layer beneath the crust. It is much thicker than the crust, about 2,900km (1,800 miles) thick. The mantle makes up about two-thirds of Earth’s mass. Beneath the crust is a layer of the mantle called Mohorovicic discontinuity (we’ll just call it Moho). It is about 3-25 miles thick. The mantle is mainly solid rocks but high heat and pressure make a large part of it act more like a thick liquid, magma. The temperature of the mantle ranges from 400°C to 900°C (750°F to 1650°F). But closer to the core, it can raise to around 4000°C (7230°F). Scientists cannot observe the mantle. They study its physical makeup by making observations on Earth’s surface. In some places, melted rock from the mantle rises to the surface and they can study this rock.

Earth’s Core Finally, we are at the Earth’s core, it is about 3500 km (2174 miles) thick and makes up about one-third of Earth’s mass. The core is made up of mostly iron and nickel, with a small amount of oxygen. Earth’s core consists of two parts: the inner and outer cores. The outer core is molten, or partly melted, but high pressure keeps the inner core solid. The temperature of the core ranges from 3700°C to 6700°C (6700°F to 12000°F). This about the same temperature as the surface of the sun! Like the mantle, the core cannot be observed directly. Scientists learn about the structure of the mantle and core by studying earthquake waves. These waves change speed as they move through the different rocks of each layer.

Now to show you just how thick each layer of Earth’s interior is……

Review Questions Which layer of Earth consists mostly or iron and nickel? 2. Which layer makes up most of Earth’s mass? What keeps the inner core solid, even though the temperature is very high?

Drawing Activity Draw the following picture, color, and label: crust, inner core, mantle, outer core, and moho? D. A. B. E. C.

Have a great day!!