Select the correct answer. What is the primary way that metamorphic rocks form? A. Lava erupts from Earth and cools. B. Water, wind, and gravity move particles from one place to another. C. Rock fragments break apart and collect as sediment. D. Existing rocks join together under high heat and pressure

Existing rocks join together under high heat and pressure.

Explanation:

There are three major groups of rocks, igneous rocks, metamorphic rocks, and sedimentary rocks. Each of them has their own unique way in which they form. The igneous rocks are the basis for the formation of the other two, and they form from magma/lava that has cooled off. The metamorphic rocks form from preexisting rocks, where deep into the crust they experience high pressure and temperatures and change their properties. Sedimentary rocks form from the breaking apart from the previous two types of rocks, and later merging together under the right conditions.

The metamorphic rocks can have igneous, sedimentary, or mixed origin. In order for these rocks to form they need to be deep into the crust where the pressure and temperatures are much higher. The high pressure and temperatures lead to the merging of different types of rcoks, change their properties, and create a new type of rock. This is one of the reasons why the metamorphic rocks often have multiple colors and they are alligned like layers.