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Earth Rocks! Check out five extraordinary rock formations.

Take a trip around the planet and you'll come across incredible landscapes, from towering stone arches to massive canyons. These amazing rock formations exist because Earth is constantly changing. The shifting of tectonic plates, giant slabs of rock that form Earth's surface, can make mountains. Wind and water can sculpt stones into unusual shapes.

All types of rock formations have something in common. They formed over very long periods of time. "Rocks are fascinating because they tell the story of Earth's history," says Michele Koppes, an earth scientist at the University of British Columbia.

Here's what five unusual rock formations around the world reveal about our planet's past.

Caption: Stone arches like this one are formed by erosion

Volcanic Columns

Legend says this group of dark rock columns in Northern Ireland, known as Giant's Causeway, was made by a giant named Finn McCool. But scientists know the real creator: volcanoes. The columns are made of an igneous rock called basalt.

Between 60 million and 55 million years ago, multiple eruptions covered the area with more than 600 meters (1,970 feet) of lava. When lava cools, it contracts. If it cools very slowly, the rock can crack, forming six-sided columns. "Mud in a puddle drying out on a hot day will form very similar patterns," says park ranger Cliff Henry. "It all has to do with physics."

Over time, erosion by ice and seawater exposed the columns. The landscape often surprises visitors. "Some people don't believe it's natural; they think it's human-made," says Henry.

The largest columns are 49 feet tall

Amazing Arches

The arch to the left soars 14 meters (46 feet) above ground. It's one of more than 2,000 rock arches at Arches National Park in Utah. The arches are made of sandstone, a type of sedimentary rock.

Between 220 million and 165 million years ago, the area was covered with giant sand dunes. Over time, the sand grains were pressed together. Minerals glued the grains into stone. The arches formed when water dissolved the minerals inside the softer sandstone. That caused the rock to crumble, carving the harder sandstone into bridge-like shapes.

Erosion is ongoing, says park ranger Lee Ferguson. New arches form--and collapse--all the time. Since the 1980s, the park has lost about 50 arches. "The rocks are constantly changing," Ferguson says.

Miles of Salt

This huge expanse of white is the world's largest salt flat. The deposit of salt in Bolivia, known as the Uyuni Salt Flat, spans 10,582 square kilometers (4,086 square miles)! That's twice as large as the state of Delaware.

More than 15,000 years ago, the area was a lake. The lake was formed by rainwater and snowmelt coming off the nearby Andes Mountains. The flowing water carried salt and other minerals from the mountains. Overtime, the lake dried up. The minerals sank to the lake bed, forming a salt flat up to 10 meters (33 feet) thick.

When it rains, a thin layer of water pools at the surface. The water reflects the sunlight, turning the salt flat into a giant mirror.

Folded Rocks

Crunch! These rocks on the Greek island of Crete look like they've been smashed together. But more than 45 million years ago, they lay flat at the bottom of the sea. The rocks are made of layers of limestone and silica, types of sedimentary rock made of shells from tiny marine animals.

As tectonic plates pressed against each other, the rock layers were slowly squeezed. Over millions of years, those tectonic forces created the folds and pushed the rocks out of the sea, says Charalampos Fassoulas, a geologist at the University of Crete.

You can find folded rocks in many places around the world. Keep an eye out for them when you're hiking!

The folded rocks are made of tiny pieces of shells.

Underwater Cave

Looking at the photo to the left, you might wonder: Did someone poke a hole in the middle of the seafloor? This round hole off the coast of Belize is known as the Great Blue Hole. It's a sinkhole leading to a deep underwater cave!

The cave started forming about 150,000 years ago, when the area was above water. Rain seeped through soil into the underground limestone. The water dissolved the limestone, creating a cave about 122 meters (400 feet) deep, says John Pohlman at the U.S. Geological Survey.

In the thousands of years since, the sea level has risen. The cave eventually filled with water. Its roof collapsed, forming a sinkhole. That's the large circular opening you can see today!

words to know

tectonic plates--slabs of rock that make up Earth's crust, or rocky outer layer

igneous rock--a type of rock that forms when rock melts deep underground, then cools and hardens

erosion--the process by which wind, water, and ice gradually wear away soil or rock

sedimentary rock--a type of rock that forms when layers of sediment, like dirt and sand, get pressed together

minerals--solid substances that form in rocks

sinkhole--a hole that forms when underground rock is worn away by water

READING LEVELS: Lexile 870 / Guided Reading Level U

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Explain how the three main types of rocks form over time.



Core Idea: ESS2.A: Earth materials and systems

Practice: Obtaining, evaluating, and communicating information Crosscutting Concept: Stability and change

COMMON CORE: Reading Informational Text:

1. Ask and answer questions to demonstrate understanding of a text. TEKS:

Science: 4.7B, 5.7A, 6.10B ELA: 3.6B, 4.6B, 5.6B, 6.5B

Lesson Plan

(1) Pre-assess students' knowledge about rocks.

Distribute the skills sheet "What Do You Know?," available at / superscience. Ask: What do you know about rocks? What do you want to know?

Tell students to complete the first two sections in their KWLS charts.

(2) Read the article and record information about rock types.

Have students read the article in small groups. Then students should write what they learned in the third section in their KWLS charts and record questions they still have in the last section.

(3) Analyze data from a map.

Distribute the skills sheet "Rock Country" (T7). Have students examine the map. Ask: Which type of rock wasn't mentioned in the article? Then read the introduction and review the definition of metamorphic rock. Have students work independently to examine where the three main types of rocks are found in the U.S. Then students should write down additional information that they learned and what they still want to know in their KWLS charts.

(4) Model the formation of rocks.

Gather materials a day before this modeling activity. Each group needs 2 squares of wax paper, scissors, 10 pieces of Starburst candies of different colors, and a microwave-safe bowl. You will need access to a hair dryer and a microwave.

Have students work in groups to unwrap and cut their candy into small, unequal pieces. Then have students press the pieces together to form a ball. This models the formation of sedimentary rocks.

Students will then place the ball onto one wax-paper square. Use a hair dryer to soften each group's ball of candy. Tell students to put the second wax-paper square over the softened candy blob and put pressure on it using heavy books. This models the formation of metamorphic rocks.

To show how igneous rocks form, students should roll their candy back into a ball and place it in the bowl. Help students completely melt the candy in the microwave for about 15 seconds. Allow it to cool.

Then ask: How did this activity model how rocks form? In what ways was this activity different from what happens in the real world?


available at

Skills sheets:

Rock Country (T7): Use a map to answer questions about where types of rocks are found in the U.S.

No-Sweat Bubble Test (TIO): Answer multiple-choice questions about the article.

What Do You Know? (online only): Use a graphic organizer to ask and answer questions about the article.


Rock Country

In "Earth Rocks!" (pp. 10-13), you learned that some rock formations are made from igneous and sedimentary rocks. Metamorphic rocks are another type of rock. These rocks form when igneous or sedimentary rocks have been changed by extreme heat and pressure. The map below shows where rocks are found on the surface in the continental U.S. Study the map, then answer the questions.


1. In the U.S., which type of rock is most commonly found on the surface? __________

2. Which of these state's surfaces contain igneous, metamorphic, and sedimentary rocks?

(A) IA (Iowa)

(B) NY (New York)

(C) TX (Texas)

(D WY (Wyoming)

3. Circle the area on the map where you live. What surface rock type(s) are found in your state? ________________

4. Use the compass to describe where most of the igneous rocks in the U.S. are located. _______________

5. Where are volcanoes located in the continental U.S.? Use evidence from the map to support your answer. ___________


* Rock Country (Reproducible, T7)

1. sedimentary 2. d 3. Answers will vary. 4. Igneous rocks are mainly found in the northwestern, western, and southwestern U.S. 5. Igneous rocks form from the cooling of volcanic lava. These rocks are found throughout the western U.S., indicating that volcanoes are found there.


No-Sweat Bubble Test

Read each question below, then use the article "Earth Rocks!" (pp. 10-13) to determine the best answer. Completely fill in the bubble next to the best answer.

1. Which Earth process can create mountains?

(A) shifting tectonic plates

(B) erosion from wind

(C) erosion from water

(D) none of the above

2. The author states, "When lava cools, it contracts." Which of the following is the best definition for contract?

(A) to die

(B) to hire

(C) to grow

(D) to shrink

3. Why might visitors be surprised by the volcanic columns at Giant's Causeway in Northern Ireland?

(A) They look like they were made by people.

(B) A giant made them.

(C) They are made of shells.

(D) They contain metals.

4. What type of rock is sandstone?

(A) igneous

(B) sedimentary

(C) volcanic

(D) all of the above

5. How does sandstone form over time?

(A) Minerals glue compressed sand grains together, turning sand to stone.

(B) Tectonic plates push against each other.

(C) Water erodes bits of rock over time.

(D Lava from a volcano cools and hardens.

6. What precious metal is found in the Uyuni Salt Flat?

(A) copper

(B) gold

(C) lithium

(D) silver

7. How did the Great Blue Hole off the coast of Belize form?

(A) Fragments of shells piled up.

(B) A lake dried up.

(C) Rock layers were squeezed together.

(D) An underwater cave's roof collapsed.

8. Which sentence from the article best supports the claim that rocks tell the story of Earth's history?

(A) "[The arch is] one of more than 2,000 rock arches at Arches National Park in Utah."

(B) "The water reflects the sunlight, turning the salt flat into a giant mirror."

(C) "But more than 45 million years ago, [these rocks] lay flat at the bottom of the sea."

(D) "You can find folded rocks in many places around the world."

9. Which detail is most important to include in a summary of the article?

(A) Utah was once covered with giant sand dunes.

(B) These rock formations exist because Earth is constantly changing.

(C) Rocks lay at the bottom of lakes.

(D) You can find folded rocks in many places.

10. How does the author present information about how each rock formation in the article came to be?

(A) by comparing and contrasting each rock formation

(B) by explaining a series of events in order

(C) by stating a problem and discussing a solution

(D) by describing several examples of each rock formation


* No-Sweat Bubble Test (Reproducible, T10)

1. a 2. d 3. a 4. b 5. a 6. c 7. d 8. c 9. b 10. b

Caption: Rain transforms the salt flat into a giant mirror!

Caption: The salt is rich in Lithium, a metal used to make lightweight batteries.

Caption: The Great Blue Hole is about 1,000 feet across and 400 feet deep.
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Title Annotation:earth science
Author:Potenza, Alessandra
Date:Apr 1, 2019
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