Earth's Layers and Plate Tectonics
Grade 5 · Science · Study Guide
Journey to the center of the Earth and discover how moving tectonic plates shape our planet's surface.
Earth is not a solid ball of rock — it is made of distinct layers, each with different temperatures, pressures, and compositions. Think of it like a hard-boiled egg: the thin shell is like Earth's crust, the egg white is like the mantle, and the yolk is like the core. Understanding these layers explains earthquakes, volcanoes, and why the continents look the way they do.
The crust is Earth's outermost layer — thin and rocky. Continental crust (under the continents) is about 25-70 km thick and made mostly of granite. Oceanic crust (under the ocean floors) is thinner (5-10 km) but denser, made mostly of basalt. Beneath the crust is the mantle, a thick layer of hot, solid rock that can flow very slowly like toothpaste over millions of years. Below the mantle is the core, divided into a liquid outer core (mostly iron and nickel) and a solid inner core. The outer core's movement generates Earth's magnetic field, which protects us from harmful solar radiation.
Earth's crust and upper mantle are broken into about 15 large pieces called tectonic plates that slowly move on top of the partially molten asthenosphere. At convergent boundaries, plates collide — oceanic plate diving beneath continental plate can cause volcanoes; two continental plates colliding can form mountain ranges like the Himalayas. At divergent boundaries, plates pull apart — this is happening right now under the Atlantic Ocean, creating new seafloor. At transform boundaries, plates slide past each other, causing earthquakes like those along the San Andreas Fault in California.
The continents were once a single supercontinent called Pangaea about 250 million years ago. Evidence includes matching rock layers on opposite sides of the Atlantic and identical fossils found in South America and Africa — continents that are now 5,000 miles apart.
| Layer | Depth | State | Composition |
|---|---|---|---|
| Crust | 0-70 km | Solid | Granite (continental), Basalt (oceanic) |
| Mantle | 70-2,900 km | Solid but flows slowly | Iron, magnesium silicate rock |
| Outer Core | 2,900-5,150 km | Liquid | Molten iron and nickel |
| Inner Core | 5,150-6,371 km | Solid | Iron and nickel under extreme pressure |
Key terms
- Crust
- Earth's thin outermost layer of rock; includes continental and oceanic crust.
- Mantle
- The thick layer of hot, semi-solid rock between the crust and core.
- Core
- Earth's innermost layer; liquid outer core and solid inner core, both mostly iron and nickel.
- Tectonic plates
- Large pieces of Earth's crust and upper mantle that slowly move on the asthenosphere.
- Convergent boundary
- Where two tectonic plates move toward each other, causing mountains or volcanoes.
- Divergent boundary
- Where two tectonic plates move apart, creating new crust and ocean ridges.
- Pangaea
- The ancient supercontinent that broke apart about 250 million years ago to form today's continents.
Flashcards
- Crust
- Earth's outermost rocky layer — thin (5-70 km) and the surface we live on.
- Mantle
- The thick middle layer of Earth; hot solid rock that flows slowly over millions of years.
- Core
- Earth's innermost layer; liquid outer core and solid inner core, made of iron and nickel.
- Tectonic plates
- Large sections of Earth's crust and upper mantle that move on the asthenosphere.
- Pangaea
- The supercontinent that existed ~250 million years ago and split into today's continents.
- Convergent boundary
- Where plates collide, forming mountains (two continental plates) or volcanoes (oceanic meets continental).
Practice questions
What are the layers of Earth in order from the surface to the center?
- Core, Mantle, Crust
- Crust, Mantle, Core
- Mantle, Crust, Core
- Core, Crust, Mantle
Show answer
Answer: Crust, Mantle, Core
From surface to center: crust (thinnest) → mantle (thickest) → outer core (liquid) → inner core (solid).
Tectonic plates move several feet per second.
Show answer
Answer: False
Tectonic plates move incredibly slowly — typically 1 to 10 centimeters per year, about as fast as your fingernails grow.
The ancient supercontinent that eventually split into today's continents is called ___.
Show answer
Answer: Pangaea
Pangaea (meaning 'all land' in Greek) began breaking apart about 175-200 million years ago. Evidence includes matching fossils and rock formations on separated continents.
At which type of boundary do two plates pull apart, creating new ocean floor?
- Convergent boundary
- Transform boundary
- Divergent boundary
- Subduction zone
Show answer
Answer: Divergent boundary
At divergent boundaries, plates move apart and magma wells up to create new oceanic crust — the Mid-Atlantic Ridge is a famous example, growing the Atlantic Ocean wider each year.
Earth's magnetic field is generated by movement in the liquid outer core.
Show answer
Answer: True
The movement of molten iron in the outer core creates electrical currents that generate Earth's magnetic field — the magnetosphere that shields us from the Sun's harmful charged particles.
Fun facts
- The temperature at Earth's inner core is about 10,000°F — as hot as the surface of the Sun — but it stays solid because the pressure squeezing it is so immense.
- The Himalayas, home to Mount Everest, are still growing about 5 millimeters per year as the Indian Plate continues to push into the Eurasian Plate.
Get a personalized course on Earth's Layers and Plate Tectonics built around your child.