How do we know, when nobody has ever been down there?

When an earthquake shakes the ground, its waves travel right through the Earth. Scientists track how those waves move. One kind of wave can't travel through liquid, and on the far side of the Earth, it goes missing. That's how we know the outer core is liquid metal.

Why is the inner core solid when it's so hot?

The inner core has the whole rest of the planet pressing in on it from every side. That squeeze is so strong it packs the iron too tightly to melt. Up in the outer core, there's less weight pressing in, so the metal there stays liquid.

What's inside the Earth?

Zib answers for ages 8–11, then goes 2 steps deeper each time a child asks why.

Zib says

Under your feet is the crust, a shell of rock about 30 kilometres thick under the land. Below it is the mantle, hot rock as gooey as thick caramel. Deeper still is the outer core, made of liquid metal. Right in the middle sits the inner core, a solid ball of iron and nickel at about 5,400 degrees Celsius.

For ages 8–10

Checked against Earth facts (NASA Science)
How do we know, when nobody has ever been down there?

When an earthquake shakes the ground, its waves travel right through the Earth. Scientists track how those waves move. One kind of wave can't travel through liquid, and on the far side of the Earth, it goes missing. That's how we know the outer core is liquid metal.

For ages 9–11

Checked against Core (National Geographic Education)
Why is the inner core solid when it's so hot?

The inner core has the whole rest of the planet pressing in on it from every side. That squeeze is so strong it packs the iron too tightly to melt. Up in the outer core, there's less weight pressing in, so the metal there stays liquid.

For ages 10–11

Checked against Core (National Geographic Education)