GEOLOGY

Detailed explanation-1: -Tectonic plates, large slabs of rock that divide Earth’s crust, move constantly to reshape the Earth’s landscape. The system of ideas behind plate tectonics theory suggests that Earth’s outer shell (lithosphere) is divided into several plates that glide over the Earth’s rocky inner layer above the soft core (mantle).

Detailed explanation-2: -Earth’s crust is divided into two types: oceanic crust and continental crust. The transition zone between these two types of crust is sometimes called the Conrad discontinuity. Silicates (mostly compounds made of silicon and oxygen) are the most abundant rocks and minerals in both oceanic and continental crust.

Detailed explanation-3: -The earth’s crust is broken into separate pieces called tectonic plates (Fig. 7.14). Recall that the crust is the solid, rocky, outer shell of the planet. It is composed of two distinctly different types of material: the less-dense continental crust and the more-dense oceanic crust.

Detailed explanation-4: -Starting roughly 4 billion years ago, cooler parts of Earth’s crust were pulled downwards into the warmer upper mantle, damaging and weakening the surrounding crust. The process happened again and again, the authors say, until the weak areas formed plate boundaries.