The answer is<em> cooler, denser crust sinks into the mantle.</em>
Explanation:
We live on Earth's crust, its thinnest and outermost layer. This layer is made from many smaller pieces called tectonic plates. These plates are not immobile; they are constantly moving to get closer to or further from each other. One of the main driving forces for tectonic plates movement is slab pull. Not all plates have the same density or temperature; oceanic plates are usually denser and colder the continental ones. Slab pull occurs when these two plates come completely next to each other and the denser oceanic plate subducts the continental, which means that it starts sinking below it, towards the asthenosphere (upper mantle), so the correct answer is cooler, denser crust sinks into the mantle.
