Unit E Lesson E9 The Rock Cycle
Completion requirements
Lesson E9: The Rock Cycle
Video Lesson
This may be difficult to comprehend: Every rock on Earth has always been here. Even more interesting is that every rock on Earth has changed at some time in the past. Rocks are always changing in what are usually slow, continual cycles that can take millions
or even billions of years.
Lesson E9: The Rock Cycle
Recycling Rocks
Rocks are classified as igneous, sedimentary, or metamorphic based on how they were formed. Igneous rocks form when molten magma and lava cool into solid rock. Sedimentary rocks form from weathering, erosion, and sedimentation of other rocks. Metamorphic rocks form when heat and pressure cause other rocks to transform into a new type of rock. All these changes and processes can be represented in a clever recycling diagram called the rock cycle. The rock cycle is a never-ending recycling of rocks that are changing from one class into another.
Rocks are classified as igneous, sedimentary, or metamorphic based on how they were formed. Igneous rocks form when molten magma and lava cool into solid rock. Sedimentary rocks form from weathering, erosion, and sedimentation of other rocks. Metamorphic rocks form when heat and pressure cause other rocks to transform into a new type of rock. All these changes and processes can be represented in a clever recycling diagram called the rock cycle. The rock cycle is a never-ending recycling of rocks that are changing from one class into another.
Reading for This Lesson
Science in Action 7
Materials:
Science in Action 7
Reading: Pages 385–390
Materials:
No other materials are required for this lesson.
Figure E.2.9.1 – Sediments gather where a river empties into a shallow sea.
Figure E.2.9.2 – Heat from magma and lava can cause nearby rock to become metamorphic.
Recycling Rocks
Rocks are classified as igneous, sedimentary, or metamorphic based on how they were formed. Igneous rocks form when molten magma and lava cool into solid rock. Sedimentary rocks form from weathering, erosion, and sedimentation of other rocks. Metamorphic rocks form when heat and pressure cause other rocks to transform into a new type of rock. All these changes and processes can be represented in a clever recycling diagram called the rock cycle. The rock cycle is a never-ending recycling of rocks that are changing from one class into another.
Figure E.2.9.3 – A simple version of the rock cycle
Figure E.2.9.4 – Ammolite is a gemstone found only in Alberta.
Figure E.2.9.5 – Great accomplishment, dude, but that’s not the “rock cycle” we want!
Figure E.2.9.6
– The Rock Cycle.
The Rock Cycle: Igneous Rocks
The rock cycle has no real beginning or ending. On the diagram, arrows represent changes between the types of rocks, but look closely at Figure E.2.9.6. Some of the arrows point in both directions. The changes in the rock cycle can take place at different speeds, but most often the changes are very slow.
The rock cycle has no real beginning or ending. On the diagram, arrows represent changes between the types of rocks, but look closely at Figure E.2.9.6. Some of the arrows point in both directions. The changes in the rock cycle can take place at different speeds, but most often the changes are very slow.
Figure E.2.9.7 – Lava that was once flowing across the land has become igneous rock.
Find “Igneous rock” on the rock cycle diagram. Igneous rocks form as lava and magma cool. The lava and magma form from melting metamorphic rock. We know this because, even if sedimentary rock suddenly plunges into a magma chamber, it changes into metamorphic
rock briefly before melting into liquid rock.
Igneous rocks can change as well. Look at the two arrows on the rock cycle diagram that point away from “Igneous rock”. Intense heat and pressure can change igneous rock into metamorphic rock. Or, weathering and erosion can change igneous rock into sediments that can eventually form sedimentary rock. Of course, the igneous rock can re-melt back into a liquid until it cools again into another igneous rock.
Igneous rocks can change as well. Look at the two arrows on the rock cycle diagram that point away from “Igneous rock”. Intense heat and pressure can change igneous rock into metamorphic rock. Or, weathering and erosion can change igneous rock into sediments that can eventually form sedimentary rock. Of course, the igneous rock can re-melt back into a liquid until it cools again into another igneous rock.
The Rock Cycle: Sedimentary Rocks
Using the diagram (Figure E.2.9.6), we can follow the fate of a sedimentary rock easily.
Erosion can break a sedimentary rock into sediments again. Another fate of sedimentary rock is being heated and pressed into metamorphic rock. For sedimentary rock, the rock cycle is a simple two-way street!
Figure E.2.9.8 – Sedimentary rocks can form in layers that are thick or thin and that contain a wide variety of materials deposited within them.
Figure E.2.9.9 – Metamorphic rocks such as marble can have twisting and turning lines of minerals that form under intense heat and pressure.
The Rock Cycle: Metamorphic Rocks
Metamorphic rocks have the most interesting possibilities in the rock cycle. They can break into sediments, melt into magma, or repeatedly be reformed by heat and pressure into various types of metamorphic rock (Figure E.2.9.6).
Scientists can obtain excellent clues about Earth’s crust from metamorphic rocks. The way the minerals organize in a metamorphic rock reveal the temperatures and pressures it must have been experienced.
Metamorphic rocks have the most interesting possibilities in the rock cycle. They can break into sediments, melt into magma, or repeatedly be reformed by heat and pressure into various types of metamorphic rock (Figure E.2.9.6).
Scientists can obtain excellent clues about Earth’s crust from metamorphic rocks. The way the minerals organize in a metamorphic rock reveal the temperatures and pressures it must have been experienced.
Try It!
Rock Cycle Activities
These activities are an excellent way to learn more about the rock cycle.
Instructions:
Click on the following two links to be taken to rock cycle activities. Follow the instructions at each activity. These activities may ask you to activate Flash on your computer – if you can't get them to work, that's OK, this practice activities are optional.
These activities are an excellent way to learn more about the rock cycle.
Instructions:
Click on the following two links to be taken to rock cycle activities. Follow the instructions at each activity. These activities may ask you to activate Flash on your computer – if you can't get them to work, that's OK, this practice activities are optional.
Figure E.2.9.10 – Most of the rocks in Alberta are sedimentary.
Figure E.2.9.11 – The huge Okotoks erratic is a metamorphic boulder made of quartzite.
The Rock Cycle in Alberta
If we could dig a trench 6000 metres deep, we would see that most of Alberta is covered in layers of thick sedimentary rock. In most parts of the province, the very top layers (the top 50 metres) are probably a jumble of dirt, sand, and various rocks called overburden. This is left over from the glaciers scraping and plowing their way across the landscape.
Below the overburden are the layers of sedimentary rock that formed millions of years ago, including layers of coal and areas of oil sands. What is under all that sedimentary rock? Deep below is same rock that makes up the Canadian Shield – huge sections of igneous and metamorphic bedrock. This rock is billions of years old and is the huge continental tectonic plate on which North America sits.
If we could dig a trench 6000 metres deep, we would see that most of Alberta is covered in layers of thick sedimentary rock. In most parts of the province, the very top layers (the top 50 metres) are probably a jumble of dirt, sand, and various rocks called overburden. This is left over from the glaciers scraping and plowing their way across the landscape.
Below the overburden are the layers of sedimentary rock that formed millions of years ago, including layers of coal and areas of oil sands. What is under all that sedimentary rock? Deep below is same rock that makes up the Canadian Shield – huge sections of igneous and metamorphic bedrock. This rock is billions of years old and is the huge continental tectonic plate on which North America sits.
Figure E.2.9.12 – Igneous rocks are rare in Alberta. The band of pillowy rock you see here is igneous.
Figure E.2.9.13 – Ammonites were ancient sea creatures with spiral shells.
Figure E.2.9.14 – Most ammonite fossils are shells, which are hard and do not decay.
Where does ammolite fit? Ammolite is a very special sedimentary rock that began to form about 75 million years ago when the Rocky Mountains were being formed. At that time, Alberta was submerged completely under a sea.
Figure E.2.9.15 – Ammolite is a rare gemstone that formed when ammonite shells became buried in layers of mud sediments in southern Alberta. Photo by
Jessa and Mark Anderson.
The Alberta part of the sea had very good conditions for sea life, including huge shelled creatures called ammonites that grew up to a metre in diameter! When the ammonites died, they sank to the bottom of this sea. Their soft body parts decayed quickly,
but their hard shells did not.
In the meantime, rains fell on the slopes of the growing Rocky Mountains. Weathering and erosion washed many sediments from the mountains into the nearby sea, covering the ammonite shells with mineral-rich mud and clay. The combination of the minerals of the ammonite shells, the minerals in the sediments, and the conditions they were buried in allowed a chemical process to occur. The result was the beautiful, flat sections of ammolite gemstone where the sections of shells used to be. For this reason, ammolite is Alberta’s official gemstone.
In the meantime, rains fell on the slopes of the growing Rocky Mountains. Weathering and erosion washed many sediments from the mountains into the nearby sea, covering the ammonite shells with mineral-rich mud and clay. The combination of the minerals of the ammonite shells, the minerals in the sediments, and the conditions they were buried in allowed a chemical process to occur. The result was the beautiful, flat sections of ammolite gemstone where the sections of shells used to be. For this reason, ammolite is Alberta’s official gemstone.
Think • Interpret • Decide
Candy Rock Cycle
To model the three types of rocks – sedimentary, metamorphic, and igneous – as well as some of their changes, observe what happens to candy when it is exposed to heat and pressure.
The video shows an experiment using candies to model these rocks and their changes. You might try the experiment yourself, using a hot water bath for the heat source. Be very careful not to use water that is too hot; you do not want to burn yourself! (Perhaps an older person with cooking experience should be in the kitchen to assist you.)
To model the three types of rocks – sedimentary, metamorphic, and igneous – as well as some of their changes, observe what happens to candy when it is exposed to heat and pressure.
The video shows an experiment using candies to model these rocks and their changes. You might try the experiment yourself, using a hot water bath for the heat source. Be very careful not to use water that is too hot; you do not want to burn yourself! (Perhaps an older person with cooking experience should be in the kitchen to assist you.)
After you have watched the video and tried the experiment yourself, do the following.
Sedimentary rock is shown as the three candies gently squeezed together. Metamorphic is shown as the candies warmed and squeezed harder. Igneous is shown as melted candy that has cooled into a new type of solid rock.
The sedimentary rocks do not form; they just appear at the start of the experiment. The igneous rock includes only the three original candies; real igneous rocks would cool from magma that includes materials from surrounding “candies” as well.
The candies would be grated or ground down into small pieces that would resemble sediment. The particles of each candy colour could be sprinkled into a layer, or gently deposited in a glass of water. Once all of the particles had been deposited, the glass
would be left to dry and the layers of coloured particles would form an example of a sedimentary rock.
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to
guide your learning.
Unit E Lesson 9 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
- DOWNLOAD the self-check quiz by clicking here.
- ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
- COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
-
REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
- SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
- CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Self-Check Time!
|
|
Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
The rock cycle is a description of the processes that occur as rocks change. Minerals and other materials make up rocks. The rock cycle reuses the same materials every time a rock changes -- over and over.
Igneous rocks form from cooling magma and lava. Because magma and lava are mixtures of various melted rocks, there is no way to know what type of rocks are in an igneous rock.
The pressure that forms sedimentary rock from loose sediments comes from the weight of the materials above the sediments. This can be the weight of other materials (usually other layers of sediments and other sedimentary rocks) above the compressed sediments, but it can include the weight of the water above the sediments in a lake or ocean, too.
Diamonds form from high heat and pressure, so they are metamorphic. You are correct to say that diamonds are metamorphic rocks and/or minerals. They are minerals (the hardest mineral, a 10 on Moh’s hardness scale) because they are pure carbon.
Both ammolite and fossil fuels form from processes that involve former living things. However, that is where the similarities end. Ammolite is a gemstone that forms in the place of ancient seashells. It did not form from actual organic matter but from the shell of the organic matter. Fossil fuels contain the carbon of all that dead life; ammolite is made of the minerals that replaced the ammonite shells.