Earth’s Materials and Processes-Part 8 Investigating Earth’s Interior

Evidence for Earth’s Interior Scientists have drilled rock samples that give insight into Earth’s interior. Volcanoes carry rocks to the surface from depths of more than 100 km. Some rocks in mountain ranges show evidence that they formed deep within Earth’s crust, and were elevated as mountains formed. In laboratories, scientists have used models to recreate rock conditions similar to those inside Earth to see how the conditions affect rock.

Evidence for Earth’s Interior Seismic waves from earthquakes can be used to make inferences about Earth’s interior. Geologists record and study seismic waves and how they travel through Earth when earthquakes occur. The paths of seismic waves reveal where the makeup or form of the rocks changes.

Earth’s Layers Scientists know that Earth’s interior is made up of three main layers: crust, mantle, and core. These layers vary in thickness, composition, temperature, and pressure. The temperature inside earth increases as the depth increases. The deeper inside Earth, the greater the pressure becomes.

The Crust The rock that forms Earth’s outer layer Includes dry land and ocean floor Main elements are Oxygen and Silicon Thinner than the layers beneath it-in most places, the crust is between 5 and 40 km thick. Oceanic crust is thinner than continental crust.

The Crust Continental crust forms the continents, oceanic crust forms the sea floor. Oceanic crust is much like basalt, or a small, fine-grained rock. Small amounts of ocean sediment can be found on top. Continental crust is much like granite-light in color with coarse grains.

The Mantle Located directly below the crust Contains more magnesium and iron than the rock above it. Has a solid component located right below the crust (Upper Mantle). Scientists have grouped the solid portion of Earth’s interior into a group called the Lithosphere (Crust and Upper Mantle)

The Mantle The lithosphere is about 100 km thick. Below the lithosphere, the material becomes increasingly hotter, causing it to be less rigid. This part of the mantle is called the asthenosphere. Beneath the asthenosphere is the lower mantle, which is hot, rigid, and under intense pressure.

The Core Below the mantle is Earth’s dense core The outer core is 2,260 kilometers thick. The inner core is a solid ball with a radius of about 1,220 kilometers. In total, the core has a total radius of 3,480 km.

The Core The outer core is a layer of molten metal surrounding the inner core. Despite enormous pressure, the outer core is liquid. The inner core is a dense ball of solid metal. In the inner core, extreme pressure squeezes iron and nickel so they cannot separate and become liquid, despite the temperatures.

The Core and Earth’s Magnetic Field Scientists believe this is caused by movements in the liquid outer core. This is the reason why a compass works. The compass aligns with Earth’s magnetic field.

Movements in the Mantle Transfer of heat in the mantle drives the process called convection. This process is how matter and energy are cycled through Earth’s interior and surface. Convection currents occur as the temperature of a substance rises, the heated substance expands, and its density decreases. It then flows up through denser (cooler) fluids.

Movements in the Mantle Heat from the core and from the mantle itself drive the convection currents. They carry hot, solid rock from the mantle outward, and cool solid rock inward. As the oceanic lithosphere cools and sinks, it drives a pattern of mantle convection.

Movements in the Mantle The cold lithosphere moves down into the mantle, where it is heated. An upward return flow of hot rock completes the cycle. Over and over, the cycle of sinking and rises takes place. One full cycle takes millions of years. Convection currents aid in the production of new rocks. Convection Currents are also found in the outer core.