Contents of 12.4 What is the evidence that subduction occurs at convergent plate boundaries?

Subduction is possible where old lithosphere is denser than asthenosphere. Metamorphism of mafic crust to eclogite further increases the density of the subducting plate and pulls it downward in the asthenosphere like an anchor.
Where continental plates collide, high mountain ranges form because thick, low-density continental lithosphere cannot subduct.
Oceanic lithosphere is continuously consumed at convergent plate boundaries, so there is no ocean floor older than 180 million years. Continental crust cannot subduct and is mostly older than 1 billion years.

12.4 What is the evidence that subduction occurs at convergent plate boundaries?