Earth's Layers — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. The outer core is the only layer of Earth that is completely liquid.
The outer core is entirely molten iron and nickel because the temperature is high enough to melt metal, but the pressure is not yet strong enough to squeeze it solid like the inner core.
2. Earth's crust is made mostly of rock and minerals, not metal.
Unlike the iron-rich core layers, the crust is composed of lighter rock and minerals such as granite and basalt.
3. The mantle contains a soft, slowly flowing zone called the asthenosphere.
The asthenosphere is a partially melted, plasticky layer in the upper mantle that allows the rigid tectonic plates above it to slide and drift.
4. Iron and nickel are the two main metals found in both the outer core and inner core.
Scientists know the core contains iron and nickel because meteorites -- leftover building blocks of our solar system -- are made of the same metals, and seismic wave data matches this composition.
5. The rigid top part of the mantle and the crust together form the lithosphere.
The lithosphere includes both the crust and the uppermost solid mantle, forming the stiff "shell" that is broken into tectonic plates.
6. Continental crust is mainly composed of a lighter rock called granite.
Granite is a light-colored, low-density rock, which is why continental crust "floats" higher than the denser basalt of oceanic crust, forming our landmasses.
7. The inner core reaches temperatures of about 5,000 degrees Celsius.
The inner core is nearly as hot as the surface of the Sun, reaching about 5,000 degrees Celsius due to leftover heat from Earth's formation and radioactive decay.
8. The mantle makes up roughly 84 percent of Earth's total volume.
At about 2,900 km thick, the mantle is by far Earth's largest layer, taking up roughly 84 percent of the planet's total volume.
9. Oceanic crust is thinner but denser than continental crust because basalt is heavier than granite.
Oceanic crust is denser because it is made of basalt, a heavier rock than granite, which is why oceanic plates sink beneath continental plates during subduction.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Crust
→ Thin outer shell of rock where all living things exist
Liquid layer of molten iron that generates Earth's magnetic field
Mantle
→ Thickest layer made of hot rock that flows very slowly
Thickest layer made of hot rock that flows very slowly
Outer core
→ Liquid layer of molten iron that generates Earth's magnetic field
Solid ball of iron and nickel at Earth's center under extreme pressure
Inner core
→ Solid ball of iron and nickel at Earth's center under extreme pressure
Thin outer shell of rock where all living things exist
Correct matches: Crust → Thin outer shell of rock where all living things exist; Mantle → Thickest layer made of hot rock that flows very slowly; Outer core → Liquid layer of molten iron that generates Earth's magnetic field; Inner core → Solid ball of iron and nickel at Earth's center under extreme pressure.