The relative thickness of the Earth's crust is similar to the skin of an apple.

Here's why:

* Earth's Crust: The Earth's crust is the outermost layer, and it's relatively thin compared to the mantle and core.

* Apple's Skin: The skin of an apple is very thin compared to the rest of the fruit.

This analogy helps visualize the thinness of the Earth's crust in relation to the rest of the planet.