Final answer:
New Earth's crust is formed through the process of decompression melting at mid-ocean ridges, where magma rises, cools, and solidifies to create new oceanic crust. Old crust is recycled at subduction zones where it is melted back into the mantle. This balance between creation and recycling of crust prevents holes from forming down to the mantle.
Step-by-step explanation:
The formation and recycling of Earth's crust are essential processes that relate to the theory of plate tectonics. The crust is created and destroyed in a cyclical manner as part of Earth's dynamic geological activity, driven by convection currents in the mantle. Answering the question posted, option C correctly explains how new crust is formed.
At locations such as the mid-ocean ridges, like the one in the Atlantic Ocean, the movement of tectonic plates apart allows magma to rise from the mantle in a process known as decompression melting. Upon reaching the surface, this magma cools and solidifies to form new oceanic crust, primarily composed of mafic rocks like basalt and gabbro.
In contrast, the destruction of crust takes place at subduction zones, where one tectonic plate is forced beneath another, descending into the mantle where it eventually melts. A well-known example of such a zone is the Japan trench. This process contributes to the recycling of crustal materials and ensures a balance between crust creation and destruction.
Continental crust, unlike oceanic crust, is made up of various igneous, metamorphic, and sedimentary rocks, with an average composition similar to granite. Due to its thickness and lower density, continental crust does not subduct easily and is often elevated above the oceanic crust, forming continents and mountain ranges. Meanwhile, oceanic crust is more prone to subduction due to its higher density and thinner structure.