Here's how the Earth is structured from the outside in:

1. Crust: This is the outermost, thin, solid layer. It's what we live on!

2. Mantle: This is the thickest layer, located beneath the crust. It's mostly solid rock, but it behaves like a very viscous fluid over long periods.

3. Outer Core: This is a liquid layer composed primarily of iron and nickel.

4. Inner Core: This is a solid sphere of iron and nickel, despite the intense heat, due to immense pressure.

So, the mantle is sandwiched between the crust and the outer core.