Structure of Earth Practice Questions

Correct answer: Crust

The crust is the outermost solid shell of Earth, ranging from about 5 to 70 kilometers in thickness. Compared to the massive mantle and core, it represents only a tiny fraction of Earth's total mass and volume.

Correct answer: The Earth's crust and mantle

The Moho is the boundary surface between the Earth's crust and the mantle. It is characterized by a significant increase in the velocity of seismic waves as they pass into the denser rocks of the mantle.

Correct answer: Outer Core

The outer core is composed of liquid iron and nickel. The movement of these conductive fluids through convection and Earth's rotation creates electric currents, which in turn generate the geomagnetic field through the dynamo effect.

Correct answer: Solid

Despite temperatures estimated to be as hot as the surface of the sun, the inner core is solid. The immense pressure at Earth's center prevents the iron and nickel from melting, forcing the atoms into a solid crystalline structure.

Correct answer: Upper Mantle

The asthenosphere is the highly viscous, mechanically weak, and ductile region of the upper mantle. It lies just below the lithosphere and allows for the movement of tectonic plates.

Correct answer: S-waves (Secondary)

S-waves are transverse waves that can only move through solid materials because liquids do not support shear stress. The 'S-wave shadow zone' provided the primary evidence that Earth's outer core is liquid.

Correct answer: Oxygen

Oxygen makes up nearly 47% of the Earth's crust by weight, primarily existing in combination with other elements as silicate minerals. Silicon is the second most abundant element.

Correct answer: Mantle

The mantle is Earth's thickest layer, extending to a depth of nearly 2,900 kilometers. It is composed of silicate rocks rich in magnesium and iron and dominates the planet's internal volume.

Correct answer: The crust and rigid upper mantle

The lithosphere is the rigid, outermost shell of Earth. It includes the crust and the brittle upper portion of the mantle, which move together as the tectonic plates.

Correct answer: Granite

Continental crust is mostly made of granitic rocks, which have a lower density (about 2.7 g/cm³) compared to the basaltic rocks of the oceanic crust. This density difference allows continents to 'float' higher on the mantle.

Correct answer: Both temperature and pressure increase

Both temperature and pressure increase steadily with depth. The heat is generated by residual energy from Earth's formation and radioactive decay, while pressure is caused by the weight of the overlying rock layers.

Correct answer: Asthenosphere

The asthenosphere is solid but behaves plastically due to high temperatures. This slow, convection-like flow is a driving force behind the movement of the rigid lithospheric plates above it.

Correct answer: Mantle and Outer Core

The Gutenberg Discontinuity occurs at a depth of roughly 2,900 km. It marks the transition from the solid silicate mantle to the liquid iron-nickel outer core.

Correct answer: Crust, Mantle, Outer Core, Inner Core

Earth is organized into chemically distinct layers based on density. The lightest materials (crust) are at the surface, followed by the mantle, and finally the densest materials (core) at the center.

Correct answer: By analyzing seismic wave behavior

Since we cannot drill deep enough to reach the mantle or core, we use seismology. By measuring how P-waves and S-waves reflect and refract as they travel through the planet, scientists can map the internal layers.

Correct answer: Thinner and more dense

Oceanic crust is generally only 5-10 km thick and made of basalt, which is denser than granitic continental crust. Its higher density is why oceanic crust sits lower in the mantle, forming ocean basins.

Correct answer: 6,000°C

The inner core is estimated to be approximately 5,500°C to 6,000°C. This is roughly the same as the surface temperature of the sun.

Correct answer: Solid silicate rock

The mantle is composed of solid, ultramafic rock, primarily peridotite. While it can flow over geological timescales, it is not a liquid; it is a solid that exhibits plastic behavior.

Correct answer: Lehmann Discontinuity

The Lehmann Discontinuity is the boundary where seismic wave velocities increase, signaling the transition from the liquid outer core to the solid inner core.

Correct answer: A zone at the base of the mantle

The D" layer is a complex 200-300 km thick region located at the very bottom of the mantle, just above the core-mantle boundary. It is characterized by unusual seismic properties and may be where some mantle plumes originate.