Most people learn what they need about earth science by sticking their head out the window.
And who said that people have to learn about the earth's mantle by age 12? (Ans: The Carnegie Foundation) The Carnegie Units were established by industrialists who wanted to improve "Academic and Industrial Efficiency."
Compare the industrial approach to education to Aristotle's classical approach, centered around grammar, logic and rhetoric.
Education hasn't been the same since the behavioral psychologists, industrialists, and Socialists took control of the University of Chicago and Columbia Teachers College in the late nineteenth century.
I highly recommend John Taylor Gatto's "Underground History of American Education," which is available to read on-line for free. He also has videos all over YouTube.
This is 9th grade, typically ages 14-15 and more importantly their homeschooling parents sent them voluntarily for the test.