Conversation so far:
what are the 2 most abundant elements in the earth's crust
Oxygen and Silicon are the most abundant elements in the earth's crust
how much of the earth's crust is oxygen
Oxygen makes up 46.6% of the Earth's crust.
how much of the earth's crust is silicon
27.7% of the earth's crust is silicon

Question: what's the third most abundant
Self-contained rewrite: what's the third most abundant in the earths crust