2 (g.a.b.) Igneous Rocks
The time is 4.6 billion years ago. You are in a spacecraft orbiting Earth. Do you see the blue and green globe of Earth that astronauts today see from space? No—instead, Earth looks like a charred and bubbling marshmallow heated over hot coals.
Soon after Earth formed, the planet’s interior became so hot that magma formed. Lava repeatedly flowed over the surface. The lava quickly hardened, forming a rocky crust.
Soon after Earth formed, the planet’s interior became so hot that magma formed. Lava repeatedly flowed over the surface. The lava quickly hardened, forming a rocky crust.
Igneous rock: The first rocks to form on Earth probably looked like the igneous rocks that can be seen today. Igneous rock is any rock that forms from magma or lava. The name igneous comes from the Latin word ignis, meaning “fire.”
Igneous rock may form on or beneath Earth’s surface. Extrusive rock is igneous rock formed from lava that erupted onto Earth’s surface. Igneous rock that formed when magma hardened beneath Earth’s surface is called intrusive rock. The most abundant intrusive rock in continental crust is granite.
Sedimentary rock: Sedimentary rocks form when sediment is deposited by water and wind. Most sedimentary rocks are formed through a series of processes: erosion, deposition, compaction, and cementation. Erosion: In erosion, running water, wind, or ice loosen and carry away fragments of rock. Deposition:Eventually, the moving water, wind, or ice slows and deposits the sediment in layers. If water is carrying the sediment, rock fragments and other materials sink to the bottom of a lake or ocean. Deposition is the process by which sediment settles out of the water or wind carrying it.
Metamorphic Rock: Every metamorphic rock is a rock that has changed its form. In fact, the word metamorphic comes from the Greek words meta, meaning “change,” and morphosis, meaning “form.” But what causes a rock to change into metamorphic rock? Heat and pressure deep beneath Earth’s surface can change any rock into metamorphic rock. When rock changes into metamorphic rock, its appearance, texture, crystal structure, and mineral content change. Metamorphic rock can form out of igneous, sedimentary, or other metamorphic rock.
Collisions between Earth’s plates can push the rock down toward the heat of the mantle. Pockets of magma rising through the crust also provide heat that can produce metamorphic rocks. The deeper a rock is buried in the crust, the greater the pressure on that rock.
Collisions between Earth’s plates can push the rock down toward the heat of the mantle. Pockets of magma rising through the crust also provide heat that can produce metamorphic rocks. The deeper a rock is buried in the crust, the greater the pressure on that rock.