* Thin compared to the Earth's mantle: The Earth's crust is incredibly thin compared to the mantle, the layer below it. Think of the crust like the skin of an apple compared to the fleshy part underneath. The crust averages just 30 kilometers (19 miles) thick under continents and about 5 kilometers (3 miles) thick under oceans. The mantle, however, stretches down to 2,900 kilometers (1,800 miles) deep.
* Thin compared to the Earth's radius: The Earth's radius is about 6,371 kilometers (3,959 miles). The crust represents a tiny fraction of that, less than 1%.
* Variable thickness: The Earth's crust isn't uniform. It's thicker under mountains and thinner under ocean basins.
So, the answer to your question depends on what you're comparing it to. It's very thin compared to the mantle, but very significant in terms of its impact on life and the planet's surface.
