🔬 ScienceGrade 3Lesson 9
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Layers of the Earth

Lesson preview: the Mini Lesson and Vocabulary are open to everyone. Guided practice, exercises, the parent checklist and the printable PDF worksheet come with full access (free 7-day trial or membership).

Learning Objectives

  • 1Identify the four main layers of the Earth: crust, mantle, outer core, and inner core
  • 2Describe a key feature of each Earth layer
  • 3Order the four layers from the outermost to the innermost
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Mini Lesson

If you could slice the Earth in half like an apple, you would see four distinct layers inside. Each layer has a different thickness, temperature, and composition. Scientists have discovered these layers by studying earthquake waves that pass through the Earth.

The Four Layers

  • Crust — the thin, rocky outer shell we live on. It is divided into large pieces called tectonic plates. The oceanic crust (under oceans) is thinner than the continental crust (under land).
  • Mantle — the thick layer beneath the crust, made of hot semi-solid rock. It is the largest layer. Slow-moving currents in the mantle drive the movement of tectonic plates.
  • Outer Core — a layer of liquid iron and nickel. Its movement generates the Earth's magnetic field, which protects us from harmful solar radiation.
  • Inner Core — the solid center of the Earth, made mainly of iron and nickel. Despite being the hottest part, it stays solid due to the enormous pressure from all the layers above.

Key Facts

  • The crust is about 5–70 km thick — the thinnest layer.
  • The mantle is about 2,900 km thick — the thickest layer.
  • The outer core is about 2,260 km thick and is liquid.
  • The inner core has a radius of about 1,220 km and is solid.
Cutaway cross-section of the Earth showing four layersEarth shown as a circle in space with a wedge cut away. Four nested layers are visible: a thin brown crust, a thick orange-red mantle, a bright orange outer core, and a yellow inner core at the center.Layers of the EarthCrustMantleOuterCoreInnerCoreA wedge sliced out shows the four nested layers.
Earth Layers FactsFour colored rows, one for each Earth layer, showing the layer name and a key fact.Earth Layer FactsCrust:Thin rocky shell we live onMantle:Thickest layer — hot semi-solid rockOuter Core:Liquid iron — creates magnetic fieldInner Core:Solid iron — hottest part of Earth
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Remember the order from outside to inside: Crust, Mantle, Outer Core, Inner Core. You can use the initials C-M-O-I to help you recall them.

Vocabulary
Crust
The thin, solid outer layer of the Earthe.g. We build houses on the Earth's crust.
Mantle
The thick middle layer of semi-solid rock beneath the cruste.g. The mantle is the largest layer inside the Earth.
Outer Core
The liquid layer of iron and nickel surrounding the inner coree.g. Movement in the outer core creates Earth's magnetic field.
Inner Core
The solid center of the Earth made of iron and nickele.g. The inner core is the hottest part of the Earth.
Tectonic plates
Large sections of the Earth's crust that slowly movee.g. Earthquakes occur where tectonic plates meet.
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← Lesson 8: Observing Habitats Around UsLesson 10: Rocks and Minerals →