Earth's Inner Core Lesson for Kids: Definition & Facts

Instructor: Greta VanBrackle

Greta has eleven years of experience teaching third and fourth grade students in all subject areas.

The inner core is located at the very center of the Earth. We can't travel there, so most of what we know about the core is based on scientists' theories. In this lesson we will learn facts about the inner core, as well as how scientists study it.

What Is the Inner Core?

The earth is made up of several different layers. The crust is the outermost layer, followed by the mantle, then the outer core. The inner core is the deepest and hottest layer of our planet. It's about 4,000 miles below the surface. Think about this: the deepest hole we've ever dug is the Kola Superdeep Borehole, which is only about 7 miles deep. You'd have to keep going another 3,993 miles to get to the center of the earth!

The inner core is at the center of the earth.
Drawing of earth layers

Now I know you're wondering how hot it gets in there. Scientists estimate that the inner core, composed of mostly iron and nickel, can reach temperatures up as high as a whopping 10,000 degrees Fahrenheit. Compare that to a candle flame, which is only about 2,600 degrees Fahrenheit. But unlike the outer core, which is liquid, the inner core's high temperature and pressure prevent it from melting. Some scientists think that the inner core is actually a plasma - which, like liquid or gas, is a state that matter can be in - acting like a solid.

Iron is one of the main ingredients of the inner core.
Photo of iron

It's Getting Bigger Every Year

Believe it or not, the inner core is actually growing about a millimeter every single year. It grows because parts of the outer core crystallize, or turn solid, over time. This process is also known as freezing, and it happens very slowly. It would take about 91 billion years for the earth's core to completely turn solid. It's not likely this will ever happen, though, since our sun will burn out in just 5 billion years!

The Inner Inner Core

Not too long ago, scientists discovered that the inner core actually has another core inside of it! This inner inner core is about half the diameter of the inner core, and contains iron crystals on an east-west axis. This is different from the rest of the inner core, which has iron crystals on a north-south axis.

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