What main rocks is the crust made up of ?

Question

I'm writing a science essay on the layers of the earth, so I need  to get more information on the crust. Thx.

Answer 1

This looks like a good link http://classroom.synonym.com/four-elements-make-up-almost-90-earth-2592.html

 

Most of the earth is made of iron at the core. Next is oxygen in the crust as part of silicate rocks. Third is silicon found in the mantle and crust. Fourth is magnesium found in both the crust and mantle.