The Rock Cycle

Free sample questions, a clear explanation, and 5 practice skills with an AI tutor that guides without giving the answer away.

Concept Review

The Rock Cycle: Earth's Ultimate Recycling System

What if you discovered that the sidewalk beneath your feet was once part of an ancient mountain, and that mountain was once mud at the bottom of an ocean? Welcome to the rock cycle — Earth's incredible recycling program that has been running for 4.6 billion years!

Every rock on Earth belongs to one of three families, and each family tells the story of how it formed. Think of rocks as Earth's diary pages, recording different chapters of our planet's history.

The Three Rock Families

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Igneous Rocks

Born from fire! Formed when melted rock (magma) cools and hardens.

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Sedimentary Rocks

Built layer by layer! Formed when bits of rock, sand, or shells get pressed together.

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Metamorphic Rocks

Transformed by pressure! Existing rocks changed by heat and squeezing deep underground.

Here's where it gets amazing: these rock families don't stay the same forever. The Mount Rushmore monument in South Dakota is carved from granite, an igneous rock that formed 1.7 billion years ago when magma cooled deep underground. But even that ancient granite could someday become sediment in a river or transform into a metamorphic rock under pressure!

🔑 Mind-Blowing Insight

Rocks don't follow a set path through the cycle. An igneous rock doesn't have to become sedimentary, then metamorphic, then back to igneous. It can skip steps! A sedimentary rock could melt and become igneous directly, or an igneous rock could get squeezed into metamorphic without ever being sedimentary. Every pathway is possible!

The Cycle Never Stops

Right now, this cycle is happening all around us. Ocean waves are breaking down coastal cliffs into tiny pieces that will become tomorrow's sedimentary rocks. Deep underground, intense heat and pressure are transforming yesterday's rocks into new metamorphic ones. And in places like Hawaii, volcanic activity is creating brand new igneous rock from melted material.

You can model this process in your classroom using clay, sand, and heat lamps to see how pressure, temperature, and time work together to transform materials — just like Earth transforms rocks over millions of years.

Key Takeaway

That sidewalk you're standing on? It really could have been part of an ancient mountain! The rock cycle proves that Earth is constantly recycling its materials, and every rock has an epic journey through time. Nothing on Earth stays the same forever — everything is part of this incredible, never-ending transformation.

Sample questions

1. Maria finds a rock that formed when melted material from deep inside the Earth cooled and hardened. What type of rock did Maria find?

○ Sedimentary rock

○ Metamorphic rock

○ Weathered rock

✓ Igneous rock

Answer: Igneous rock — Igneous rocks form when melted rock material (magma or lava) cools and hardens. The word 'igneous' comes from the Latin word for fire, which helps us remember that these rocks form from hot, melted material.

2. True or False: A rock that forms from layers of sand and mud pressed together over millions of years is a metamorphic rock. Explain your reasoning.

○ True, because pressure was involved in making the rock

✓ False, because this describes how sedimentary rocks form from layers of materials

○ True, because it took millions of years to form

○ False, because metamorphic rocks only form from igneous rocks

Answer: False, because this describes how sedimentary rocks form from layers of materials — Sedimentary rocks form when layers of sediments (like sand, mud, or pieces of other rocks) are pressed and cemented together over time. While pressure is involved, the key feature is that they form from layers of materials, not from existing rocks being changed by heat and pressure.

3. Jake's teacher shows the class four rock formation scenarios. Which scenario describes the formation of a metamorphic rock?

○ Volcanic lava cools quickly on Earth's surface

○ Tiny shells pile up on the ocean floor and get pressed into layers

✓ An existing rock is heated and squeezed until its minerals change

○ Magma cools slowly deep underground

Answer: An existing rock is heated and squeezed until its minerals change — Metamorphic rocks form when existing rocks (igneous, sedimentary, or other metamorphic rocks) are changed by heat and pressure deep in the Earth. The original rock's minerals transform into new minerals, but the rock doesn't melt completely.

Skills in this topic

Classify rocks as igneous, sedimentary, or metamorphic based on formation
Describe the processes that form each type of rock
Trace pathways rocks can take through the rock cycle
Identify examples of each rock type in local geological formations
Model the rock cycle using classroom materials to demonstrate transformations

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