Earth Materials

Earth Materials

Middle School

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Learning Objectives

• Differentiate between the three main types of rocks: igneous, sedimentary, and metamorphic.

• Describe the rock cycle and the processes that transform one type of rock into another.

• Explain the formation and characteristics of intrusive and extrusive igneous rocks.

• Describe how heat and pressure alter existing rocks to form metamorphic rocks.

Key Vocabulary

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Rock Cycle

The series of processes that create and change rocks in Earth's crust over long periods of time.

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Igneous Rock

A type of rock formed when hot, molten magma or lava cools down and becomes solid.

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Sedimentary Rock

Rock formed from sediments, which are then compacted and cemented together over a long period of time.

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Metamorphic Rock

Rock that has changed from one form to another due to intense heat and immense pressure.

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Magma

Hot, semi-fluid material found beneath the Earth's crust from which lava and igneous rocks are formed.

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Lava

Hot molten rock that has erupted from a volcano or fissure onto the Earth’s surface.

Key Vocabulary

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Weathering

The process where rock is worn away or broken down into much smaller pieces.

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Erosion

The process where earthen materials are worn away and moved by forces like wind or water.

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Foliation

The repetitive layering in metamorphic rocks, creating bands of different colored crystals from pressure.

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Cementation

The process where dissolved minerals crystallize and glue sediment particles together into a single mass.

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What Are Rocks and the Rock Cycle?

• Rocks are classified by how they form as igneous, sedimentary, or metamorphic.

• The rock cycle is the process of one rock type changing into another.

• Energy from the Sun and Earth's interior drives the rock cycle's changes.

• Earth’s systems like the geosphere and hydrosphere interact to transform these rocks.

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Multiple Choice

What is the rock cycle?

• The way rocks are sorted by size.

• The process by which one type of rock changes into another.

• A list of all the minerals found on Earth.

• The study of the Earth's layers.

Multiple Choice

What provides the energy that drives the changes in the rock cycle?

• Energy from the Moon's gravity and ocean tides.

• Energy from plants and animals.

• Energy from the Sun and the Earth's interior.

• Energy from wind and lightning storms.

Multiple Choice

Based on the processes described, what is the best explanation for how different types of rocks like igneous, sedimentary, and metamorphic are formed?

• The interaction between Earth's systems, like the geosphere and hydrosphere.

• The process of rocks becoming harder over time.

• The classification of rocks into three main types.

• The amount of energy available from the Sun.

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Igneous Rocks: Formed from Fire

Intrusive Rocks

• Forms when magma gets trapped and cools slowly beneath Earth's surface.

• Slow cooling allows large mineral crystals to form, creating a coarse-grained texture.

• A common example of this type of rock is granite.

Extrusive Rocks

• Forms when lava erupts onto the surface and cools down very quickly.

• Rapid cooling results in very small crystals, leading to a fine-grained texture.

• Examples include basalt, pumice, and obsidian, which can have a glassy texture.

Multiple Choice

What is the primary difference between intrusive and extrusive igneous rocks?

• The location where they cool and form.

• The color of their mineral crystals.

• The continent where they are found.

• The age of the rocks.

Multiple Choice

Why do intrusive rocks like granite typically have a coarse-grained texture?

• Slow cooling allows for the growth of large mineral crystals.

• Rapid cooling traps gases, which creates large crystals.

• Slow cooling results in a fine-grained, glassy texture.

• Rapid cooling on the surface leads to coarse-grained rocks.

Multiple Choice

A geologist finds a piece of obsidian, which has a smooth, glassy texture. What is the most likely conclusion about how this rock formed?

• It formed from lava that cooled very quickly on the Earth's surface.

• It formed from magma that cooled slowly deep within the Earth.

• It has a coarse-grained texture because it cooled slowly.

• It is a type of intrusive rock with large mineral crystals.

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Sedimentary Rocks: A Story in Layers

Formation Process

• Weathering breaks down rocks into small pieces, and erosion carries them away.

• These pieces, called sediments, are deposited and settle into many different layers.

• Compaction and cementation press and glue these layers together into solid rock.

Other Formation Types

• Chemical rocks form when minerals that are dissolved in water crystallize.

• Organic rocks are made from the built-up remains of once-living things.

• Limestone is an organic rock, while rock salt is a chemical rock.

Multiple Choice

What are the final two steps that press and glue sediments together to form solid rock?

• Compaction and cementation

• Weathering and erosion

• Deposition and layering

• Crystallization and dissolving

Multiple Choice

What is the main difference in the formation of limestone and rock salt?

• Limestone is made from the remains of living things, while rock salt is formed from crystallized minerals.

• Limestone is formed by pressure, while rock salt is formed by heat.

• Limestone is made of sand, while rock salt is made of shells.

• Limestone is carried by erosion, while rock salt is formed by weathering.

Multiple Choice

Compaction and cementation press and glue the sedimented layers together into solid rock.

• The statement is correct for only Sedimentary rocks.

• The statement is correct for only Metamorphic rocks.

• The statement is correct for only Igneous rocks.

• All are true.

Metamorphic Rocks: Changed by Heat and Pressure

• Existing rocks are changed by intense heat and pressure deep within the Earth.

• Extreme pressure can create parallel bands or layers, a feature called foliation.

• For example, shale turns into slate, and limestone changes into marble.

Multiple Choice

What two conditions are responsible for changing existing rocks into metamorphic rocks?

• Heat and pressure

• Wind and water

• Melting and cooling

• Erosion and weathering

Multiple Choice

How does extreme pressure affect a rock to cause the feature known as foliation?

• It creates parallel bands or layers within the rock.

• It causes the rock to melt completely into magma.

• It breaks the rock into smaller pieces called sediment.

• It makes the rock less dense and lighter in color.

Multiple Choice

A geologist finds a metamorphic rock that has distinct, parallel layers. What can be concluded about the conditions under which this rock formed?

• The rock was likely formed under extreme pressure.

• The rock must be a type of marble.

• The rock was formed from cooled lava.

• The rock is a form of unchanged shale.

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Common Misconceptions

Misconception	Correction
Rocks are permanent and do not change.	The rock cycle shows that rocks are constantly being transformed.
The rock cycle follows a single, one-way path.	Any type of rock can change into any other type.
All sedimentary rocks are formed from pieces of other rocks.	Some are formed from minerals in water or remains of living things.

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Summary

• The three main rock types are igneous, sedimentary, and metamorphic.

• The rock cycle illustrates the continuous transformation of rocks over time.

• Igneous, sedimentary, and metamorphic rocks have unique formation processes.

• Rocks provide important clues about Earth’s geological history.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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