Final answer:
New crust is formed when tectonic plates move apart, allowing magma to rise and solidify. This process, as well as mantle plume activity, contributes to the dynamic reshaping of the Earth's surface, including mountain building and the closure of fissures in the crust.
Step-by-step explanation:
New crust is formed primarily through the process of tectonic plates moving apart at divergent boundaries, such as those found in the mid-ocean ridges. When these plates move apart, they allow magma from the mantle to rise up. This magma, upon reaching the surface, cools and solidifies to create new crust. Over time, this activity can lead to the formation of extensive mountain ranges, as well as the transformation of other geological features.
Fissures in the Earth's crust are a result of tectonic activity. When the crust breaks, it can lead to the release of water from the interior, which can flood the landscape, including craters. At convergent plate boundaries, one plate may subduct beneath another, leading to volcanic activity and the formation of new crust through processes like flux melting.
Mantle plumes also contribute to crust formation at hotspots, where increased temperatures lead to melting of the lithosphere above the plume, regardless of plate boundaries. These diverse mechanisms are continuously reshaping the Earth's surface.