Here are the layers of the Earth's interior in order of increasing density, from least to greatest:

1. Crust: This is the outermost layer, composed of relatively light materials like granite and basalt.

2. Mantle: This thick layer is mostly composed of silicate minerals and is denser than the crust.

3. Outer Core: This is a liquid layer composed primarily of iron and nickel. It is much denser than the mantle.

4. Inner Core: This is a solid ball of iron and nickel at the Earth's center. It is the densest layer due to immense pressure.

Let me know if you'd like more details on each layer!