Unit E Lesson E1 Structure of the Earth
Completion requirements
Lesson E1: Structure of the Earth
Video Lesson
Earthquakes, volcanoes, landslides, and many other acts of nature can be awesome, scary, and unpredictable. However, what occurs on the surface is only part of the story. We are not much different than ants on a beach ball: we see only the part on which
we are walking. Many of the mysteries we see on Earth’s surface can be understood better by learning about what is inside our planet.
Lesson E1: Structure of the Earth
Structure of the Earth
Earth is always changing. Sometimes it changes suddenly, but sometimes changes occur over long periods – even millions of years. The first step in understanding Earth is to learn about the materials of which it is made. That means we need a way to study the rocks, minerals, and stuff below our feet.
Earth is always changing. Sometimes it changes suddenly, but sometimes changes occur over long periods – even millions of years. The first step in understanding Earth is to learn about the materials of which it is made. That means we need a way to study the rocks, minerals, and stuff below our feet.
Reading and Materials for This Lesson
Science in Action 7
Reading: Pages 352-356
Materials:
Science in Action 7
Reading: Pages 352-356
Materials:
cardboard, scissors, white glue, masking tape, ruler, some hardcover books
Figure E.1.1.1 – In Norse mythology, earthquakes were caused by poison dripping onto Loki’s face.
Figure E.1.1.2 – Pele, the Hawaiian goddess of volcanoes. (Prayitno)
The Mystery of Earth’s Structure
Early civilizations must have been very curious about Earth’s structure. They could explore caves, dig holes, hike through canyons, and dig wells, but they could never get to the bottom. Everything would have seemed to be rocks, dirt, and sometimes water. Then, suddenly, an earthquake would destroy the village, or a nearby mountain would explode and molten lava would flow through the countryside. An island might appear suddenly in the sea, or a skeleton might be found at the bottom of a trench. Whatever was going on down there was not just rocks and dirt and sometimes water!
Without the ability to investigate further for answers, early peoples used myth and legend to explain sudden Earth events. Through their stories, people warned others that Earth could be dangerous and damaging. They knew the surface of the Earth was usually quiet, but it had to be treated with respect because they never knew what was going to happen next!
A Model of Earth’s Structure
One of the best ways to understand something is to learn where it came from. This is true when you are studying something difficult or impossible to see, such as with the structure of Earth.
One widely-accepted theory about Earth’s origin goes to the beginnings of our solar system about 4.6 billion years ago. The theory is that a huge explosion occurred, sending matter and energy throughout space. Swirling clouds of particles and gases joined slowly to form huge clumps of matter. These clumps were so massive that they had enough gravity to squish the matter in the clumps very tightly. The largest of these clumps became stars with gravity so strong that matter could become energy at their core. Smaller clumps became planets, moons, asteroids, and meteors. These had large amounts of energy at their centres, but not enough energy to become stars.
We need a model of Earth’s formation to better understand what happened. The accepted scientific model takes into account the behaviour of the stars and planets, the force of gravity, the strength of the magnetic fields, and the densities of Earth’s layers. This model of Earth’s formation is accepted by most scientists as the way all stars and planets form.
One of the best ways to understand something is to learn where it came from. This is true when you are studying something difficult or impossible to see, such as with the structure of Earth.
One widely-accepted theory about Earth’s origin goes to the beginnings of our solar system about 4.6 billion years ago. The theory is that a huge explosion occurred, sending matter and energy throughout space. Swirling clouds of particles and gases joined slowly to form huge clumps of matter. These clumps were so massive that they had enough gravity to squish the matter in the clumps very tightly. The largest of these clumps became stars with gravity so strong that matter could become energy at their core. Smaller clumps became planets, moons, asteroids, and meteors. These had large amounts of energy at their centres, but not enough energy to become stars.
We need a model of Earth’s formation to better understand what happened. The accepted scientific model takes into account the behaviour of the stars and planets, the force of gravity, the strength of the magnetic fields, and the densities of Earth’s layers. This model of Earth’s formation is accepted by most scientists as the way all stars and planets form.
Figure E.1.1.3 – Even the deepest drilling rigs cannot reach near the centre of Earth.
Figure E.1.1.4 – Swirling clouds of dust and gases join slowly to form early Earth.
Figure E.1.1.5 – A newly-formed Earth, about 4.5 billion years ago.
Learning About Earth’s Structure From It’s Origin
If you try to explore Earth’s structure, the deepest you can go is a few thousand metres, and you might send some instruments down rather than go yourself! The deepest cave we have explored is about 2 km below the surface, our deepest mine is 2.4 km to the bottom, and the deepest ever drilled is slightly more than 12 km. That sounds very deep until you realize the centre of Earth is more than 6 300 km away from where you are, and straight down!
Geologists have overcome our limited ability to dig deep by building a model of the Earth’s structure using important information from earthquake waves. Did you know that three types of earthquake waves occur? Geologists can measure all three waves quite accurately to find the location of the earthquake. They know the waves speed up, slow down, or disappear completely when they go through various kinds of material. These changes in speed reveal changes in the various layers of materials in Earth’s structure.
If you try to explore Earth’s structure, the deepest you can go is a few thousand metres, and you might send some instruments down rather than go yourself! The deepest cave we have explored is about 2 km below the surface, our deepest mine is 2.4 km to the bottom, and the deepest ever drilled is slightly more than 12 km. That sounds very deep until you realize the centre of Earth is more than 6 300 km away from where you are, and straight down!
Geologists have overcome our limited ability to dig deep by building a model of the Earth’s structure using important information from earthquake waves. Did you know that three types of earthquake waves occur? Geologists can measure all three waves quite accurately to find the location of the earthquake. They know the waves speed up, slow down, or disappear completely when they go through various kinds of material. These changes in speed reveal changes in the various layers of materials in Earth’s structure.
Figure E.1.1.6 – Earth’s layers and their approximately thickness.
Watch More
In this video, you can see how these ideas have come together to reveal a model of Earth’s structure.
Earth’s Core
At the very centre of the Earth is the core made of two parts. The inner core has a radius of about 1200 km, and it is extremely hot, perhaps as hot as the surface of the Sun! The heat and the pressure of all the matter above the inner core keeps this layer in the form of a solid. It is likely pure nickel, iron, and other heavy elements.
The outer core, approximately 2000 km thick, consists of materials similar to those of the inner core but at slightly lower temperatures and pressures. As a result, it is liquid instead of solid. This flowing liquid mass of metals produces Earth’s magnetic field, which is a very important bonus to humanity. Earth’s magnetic field protects all life on the surface from harmful solar radiation.
At the very centre of the Earth is the core made of two parts. The inner core has a radius of about 1200 km, and it is extremely hot, perhaps as hot as the surface of the Sun! The heat and the pressure of all the matter above the inner core keeps this layer in the form of a solid. It is likely pure nickel, iron, and other heavy elements.
The outer core, approximately 2000 km thick, consists of materials similar to those of the inner core but at slightly lower temperatures and pressures. As a result, it is liquid instead of solid. This flowing liquid mass of metals produces Earth’s magnetic field, which is a very important bonus to humanity. Earth’s magnetic field protects all life on the surface from harmful solar radiation.
Earth’s Mantle
The mantle is the thickest layer of the Earth, approximately 2500 km thick. Similar to the core, the mantle has two layers. The upper mantle is a solid, just as the crust above it is. The lower mantle is partly melted by the heat from the core below. It flows, moving in circular convection currents. This forms a layer of moving, melted rock similar to the slowest conveyor belt you can imagine. The sections of crust resting on the upper mantle are pushed and pulled slowly on this conveyor belt.
The combination of upper mantle and crust are given the special name of the lithosphere. A helpful way to think of the lithosphere is to think of a peanut butter and banana sandwich. Earth’s crust is the top slice of bread, the upper mantle is the banana, and the lower mantle is the gooey peanut butter that allows the bread and banana pieces to slide around.
The mantle is the thickest layer of the Earth, approximately 2500 km thick. Similar to the core, the mantle has two layers. The upper mantle is a solid, just as the crust above it is. The lower mantle is partly melted by the heat from the core below. It flows, moving in circular convection currents. This forms a layer of moving, melted rock similar to the slowest conveyor belt you can imagine. The sections of crust resting on the upper mantle are pushed and pulled slowly on this conveyor belt.
The combination of upper mantle and crust are given the special name of the lithosphere. A helpful way to think of the lithosphere is to think of a peanut butter and banana sandwich. Earth’s crust is the top slice of bread, the upper mantle is the banana, and the lower mantle is the gooey peanut butter that allows the bread and banana pieces to slide around.
Figure E.1.1.7 – Earth’s layers are similar to those of a peanut butter and banana sandwich.
Earth’s Crust
If Earth was an onion, the crust is the thin skin on the outside. This is the solid outer rock layer of Earth, but it is by far the thinnest of Earth’s layers. The crust is thinner (a few kilometres) on the bottom of the oceans, and much thicker (50 to 90 km) below mountain ranges on the continents. The crust has many minerals and fossil fuel deposits that we dig and drill for our manufacturing and energy needs.
If Earth was an onion, the crust is the thin skin on the outside. This is the solid outer rock layer of Earth, but it is by far the thinnest of Earth’s layers. The crust is thinner (a few kilometres) on the bottom of the oceans, and much thicker (50 to 90 km) below mountain ranges on the continents. The crust has many minerals and fossil fuel deposits that we dig and drill for our manufacturing and energy needs.
Try It!
Make Your Own Earth Layers
Here is a way to use density to construct a model of Earth layers.
Materials:
Here is a way to use density to construct a model of Earth layers.
Materials:
- glass or clear plastic cup
- liquid honey
- concentrated dish soap
- water
- vegetable oil
- turkey baster
Instructions:
- Pour enough honey into the cup to make a layer about 1 cm deep. Make all following layers about the same depth.
- Add dish soap, pouring very slowly.
- Add water very slowly and carefully. Tilt the cup slightly and pour along the edge or use the turkey baster.
- Add the last layer of vegetable oil very slowly and carefully.
- Observe the model of Earth layers you have made, and think about the following questions.
Questions:
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
The model has four layers, similar to Earth. However, the model has all liquid layers, which is unlike Earth that has some solid and some semi-solid layers.
You could say that the bottom layer in the model, honey, is the deepest layer of the earth – the inner core. Then, working your way up, dish soap would be the outer core, water would be the mantle, and oil would be the crust. Thinking of the water as
the lower mantle and the oil as the upper mantle also is reasonable.
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 1 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!
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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.
Scientists construct a model when the idea they are trying to explain is too big, too small, too far away, or is hidden or dangerous or does not exist anymore.
People are curious about the world, and they want to feel they understand why things are the way they seem to be. Myths and legends help explain things that cannot be seen or understood easily, and they help to pass important information to
future generations.
The theory is that stars and planets form from swirling clouds of dust, particles, and gases that are left after a huge explosion. All these pieces clump together slowly to form huge stars and planets.
The main method scientists use to determine Earth’s structure is the behaviour of earthquake waves as they pass through the Earth. Also, scientists use the force of gravity between the Earth and Moon, the strength of Earth’s magnetic field,
and the densities of various materials and how they behave with each other.
Both the outer core and the lower mantle are liquid rock that moves and flows in convection currents. However, the outer core is much hotter than the lower mantle is, and it has much more iron and nickel. The movement of these particles in the
outer core is the reason Earth has a strong magnetic field. The magnetic field helps to block much of the harmful solar radiation from the Sun that would otherwise destroy life on Earth. Thus, if the outer core became solid and non-moving,
life might soon perish because of harmful radiation. (... and Boy Scouts would be lost in the woods because their compasses wouldn’t work!)