Have you ever wondered what the earth looks like on the inside? What is it made of? How can we find out? These are great questions, considering that the center of the earth is nearly 4,000 miles (6,437 km) below its surface, making it difficult to explore!
One way to study the inside of the earth is to drill holes and examine what is found. The deepest hole that has been drilled into the earth is the Kola Superdeep Borehole, which is located on the Kola Peninsula in Russia. It is only approximately 7.5 miles (12 km) deep and 9 inches (23 cm) in diameter. The drilling had to stop because internal temperatures of 356°F (180°C) at that depth became too hot to continue!1
Even without drilling, scientists have devised interesting methods to study what lies inside the earth. Have you thrown a stone into a pond and watched as waves moved through the water? There are waves that can pass through the earth too, called seismic waves. Seismic waves are generated during earthquakes and move at varying speeds when passing through different types of solids and liquids. Scientists can collect data from the way that seismic waves behave when passing through the earth, and theorize at what is inside of it.
Earthquakes generate various seismic waves . . . that travel through the earth’s interior. By analyzing how these waves change behavior when they reach different regions, we can learn where the density changes significantly. At a depth of about 1,796 miles (2,890 km), an abrupt change indicates a sudden increase in density. This corresponds to the core-mantle boundary.
If we look at a chart of different metal densities, iron best fits the density at the core, and olivine (a magnesium-iron silicate mineral) best fits the mantle. Even though the core is made of the same basic iron material, certain seismic waves travel differently through the outer core, indicating that it must be liquid, while the inner core is solid.2
Scientists have determined that the earth layers consist of the crust, mantle, outer core, and inner core.
There is liquid water in the crust layer of the earth in pore spaces and crevices. However, there is a great deal more water found in the earth’s mantle, but it is trapped inside crystal structures, not in liquid form. This water can be released from the rock when it melts, such as occurs to produce volcanic eruptions, and may have been much of the source of the “fountains of the great deep” of the worldwide Flood recorded in Genesis 6.3
You can build a basic model of the earth to learn more about these layers!
While your model might not be to scale representing the exact depths of the different layers, it is a great way to learn about and discuss what lies beneath the surface of the earth. As you explore the wonders found inside of our world, it is easy to see that it was made by a Creator! It’s also a great reminder that God made the earth special just for us, designing the earth in a way that supports life. No other planets have been found that are like it. The Bible tells us that God made the earth in six days, around 6,000 years ago. You can read Genesis 1 to learn more about this.