Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: Continental crust is much thicker than oceanic crust. It is 35 kilometers (22 miles) thick on average, but it varies a lot. Continental crust is made up of many different rocks. All three major rock types igneous, metamorphic, and sedimentary are found in the crust. On average, continental crust is much less dense (2.7 g/cm3) than oceanic crust. Since it is less dense, it rises higher above the mantle than oceanic crust. Answer: 35 kilometers
How thick is the earth's continental crust, on average?