Rock layers and Earth's history
Interpret cross-section diagrams of the Earth's interior, geological strata, and rock cycle; read and label layers (crust, mantle, outer core, inner core); understand that deeper layers in sedimentary sequences are older
What a learner can do afterwards
- Label the four layers of the Earth on a cross-section diagram using the correct terms
- Interpret a diagram of sedimentary rock layers and identify which layer was deposited first
- Read a rock cycle diagram and trace the pathway of a rock from igneous to sedimentary to metamorphic
1 · Read
Earth is built like a hard-boiled egg. The thin shell is the crust, the ground under your feet. Under that is the mantle, a thick layer of hot rock that flows very slowly, like thick honey. Deeper still is the outer core, made of melted metal. At the very center sits the inner core, a solid ball of metal, the hottest part of the whole planet.
A scientist cuts open a cliff and sees flat bands of rock stacked like a sandwich. The bottom band formed first, long before the top band. Each new layer of sand or mud settles on top of the layer before it, so in an undisturbed stack, the deepest layer is always the oldest.
In a stack that has never been disturbed, reading rock layers is like reading a diary from the bottom up. The oldest entry sits at the bottom, and every new page gets added on top.
Rocks change from one kind to another in a cycle. Melted rock cools and hardens into igneous rock. Wind and water break igneous rock into tiny pieces that pile up and press together into sedimentary rock. Heat and pressure deep underground squeeze sedimentary rock into metamorphic rock, which can melt again and start the cycle over.
Earth has four layers, crust to inner core, and in an undisturbed stack of rock layers the bottom layer is always the oldest.
The rewritten readings were written for this dataset.
More to read
Modeling Earth's inside
A model can help you explore Earth's hidden layers. We live on its thin, rocky crust. Beneath it is the thick mantle, made mostly of solid rock that moves very slowly. The outer core consists of liquid metal. The inner core forms a hot, solid ball. Material, temperature and pressure vary between layers. Add labels to make a model you can hold and study.
Clues in Earth's outer rock
The crust, Earth's thinnest layer, contains mountains, seafloor and fossils. Oceanic crust is thinner and denser than continental crust. The crust and uppermost mantle form plates that move a few centimeters yearly. Rock can form where plates separate, while collisions can force old rock downward. Studying the crust helps us understand Earth's past.
How we study the deep Earth
From space, Earth has blue oceans, rocky land and swirling clouds. Dense metals collected in its core, while lighter rock formed outer layers. Earthquake waves change speed or direction as they cross different materials, helping scientists map the interior. They show that the mantle is mostly solid. Other evidence shows that this rock moves slowly over very long times.
Learning Assessment - Maps & Structures
Sedimentary rock stacks up in flat layers called strata. The bottom layer settled first, so it is the oldest, and the top layer is the youngest. Sometimes the stack tilts, folds, or cracks, and reading the offsets tells which event came first and which came last. Geologists draw cross sections to show these orderings clearly. With strata and the rock cycle, a single cliff face can narrate millions of years.
Explore more
2 · Watch
En anglaisTake it off screen
Where it sits
Learn first
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
24 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.