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Earth Science
Grade 6-8
Earth's Layers & Internal Structure Cheat Sheet
A printable reference covering Earth's layers, crust, mantle, core, lithosphere, asthenosphere, density, pressure, and seismic evidence for grades 6-8.
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Earth's internal structure explains what our planet is made of beneath the surface and how scientists study places humans cannot directly visit. This cheat sheet helps students compare the crust, mantle, outer core, and inner core by composition, state, density, and temperature. It also connects Earth's layers to earthquakes, volcanoes, plate motion, and magnetic fields.
Key Facts
- Earth has four main compositional layers: crust, mantle, outer core, and inner core.
- Density is calculated with density = mass / volume, and Earth's layers generally become denser with depth.
- The lithosphere includes the crust and the rigid uppermost mantle, and it is broken into moving tectonic plates.
- The asthenosphere is a softer, slowly flowing part of the upper mantle beneath the lithosphere.
- The outer core is liquid iron and nickel, while the inner core is solid iron and nickel because pressure is extremely high.
- Temperature, pressure, and density all increase as depth below Earth's surface increases.
- Seismic wave speed can be described with speed = distance / time, and changes in wave paths help reveal Earth's layers.
- S-waves cannot travel through liquids, so the S-wave shadow zone provides evidence that the outer core is liquid.
Vocabulary
- Crust
- The thin, solid outer layer of Earth made of rock, including continental crust and oceanic crust.
- Mantle
- The thick layer of hot rock between the crust and core that can slowly flow over long periods of time.
- Core
- Earth's central region made mostly of iron and nickel, divided into a liquid outer core and solid inner core.
- Lithosphere
- The rigid outer shell of Earth that includes the crust and uppermost mantle and is divided into tectonic plates.
- Asthenosphere
- The softer, hotter layer of the upper mantle that allows tectonic plates to move above it.
- Seismic Waves
- Energy waves produced by earthquakes that travel through Earth and help scientists study its internal structure.
Common Mistakes to Avoid
- Calling the mantle a liquid: the mantle is mostly solid rock that flows very slowly because it is hot and under pressure.
- Mixing up lithosphere and asthenosphere: the lithosphere is rigid and broken into plates, while the asthenosphere is softer and flows slowly.
- Saying the inner core is liquid because it is hotter: the inner core is solid because the pressure is so great that iron and nickel cannot melt easily.
- Assuming density stays the same inside Earth: density increases with depth because deeper materials are compressed by the weight above them.
- Thinking scientists have drilled to the core: humans have only drilled a small distance into the crust, so most evidence comes from seismic waves, gravity, magnetism, and rock samples.
Practice Questions
- 1 A rock sample has a mass of 180 g and a volume of 60 cm3. What is its density using density = mass / volume?
- 2 A seismic wave travels 3,000 km in 500 seconds. What is its speed using speed = distance / time?
- 3 List Earth's main compositional layers in order from the surface to the center.
- 4 Explain why S-waves disappearing on the far side of Earth is evidence for a liquid outer core.