Answer the following question given this paragraph: 

Most of the world’s largest mountains form as plates collide at convergent plate boundaries. Continents are too buoyant to get pushed down into the mantle. So when the plates smash together, the crust crumples upwards. This creates mountains. Folding and faulting in these collision zones makes the crust thicker.


Q: Why are continents unable to be pushed down into the mantle by plate boundaries?


A:
buoyancy