Chapter 4 – Planet Earth

CHAPTER INTRODUCTION

A day in the life of our home planet. This video shows a repeating loop of Earth rotating over a single day, as viewed from the Deep Space Climate Observatory (DSCOVR). Credit: NASA/NOAA.


Take a look at the mesmerizing video loop of our planet above, in which we see it rotating in the deep, black void of space. It is an amazing sight, particularly when you remember that in all of the vast universe, it is the only known place where we can survive outdoors without a spacesuit.

We’ll spend the rest of this book focusing on our relationship with Earth, exploring some of the many ways in which it affects every single aspect of our lives. As you will learn, even this planet has not always been a place where humans could survive, and it comes with no guarantees for the future. The future is up to us, and if we want that future to be a good one, we must understand the world on which we depend.

In this chapter, we’ll begin to build this understanding. We’ll start with a “big picture” overview of planet Earth. We’ll then see how we can think of our world as a set of interacting systems, driven by energy from the Sun and from Earth’s interior heat. Finally, we’ll explore how and why Earth is so different from any other world that we know of. In essence, we’ll use this chapter to create a general context for thinking about our planet, so that in the later chapters we can look in more detail at the processes that shape our world and the steps we must take to ensure our future survival.

Activity

How We Depend on Earth

Work in small groups of 3 to 5 students. Each group should spend about 5 minutes making a written list of at least 5 ways in which we depend on Earth. Then your teacher will help you combine all your lists together into a class list of the ways we depend on our planet. After you have the class list, spend a few minutes discussing the importance of our planet to our survival.

Show Teachers Notes

The goal of this activity is to come up with a class list of ways in which we depend on Earth. There are almost innumerable possible items that students could list, so we offer just a few examples here:

  • We depend on the oxygen in Earth’s atmosphere to fuel our metabolism.
  • We depend on fresh water to drink.
  • We depend on food grown in soil.
  • We depend on Earth’s gravity to avoid floating away into space.
  • We depend on the ozone layer to protect us from solar ultraviolet radiation.
  • We depend on natural resources to provide material things we use in our lives.

Given the many possibilities, we suggest proceeding as the activity indicates, by having students work in small groups to make lists of 5 or more items. We suggest limiting this to 5 minutes so that the lists do not get too long. Then you will help the students combine the lists into a single list at the front of the classroom. There are many ways to do this, but one suggestion is to have a representative from one group come write down their items. Then have the second group add any new items that are not on the first list, and put a checkmark for any items that are the same (or close enough to count as the same). Continue until you have consolidated all the lists, then engage in a bit of class discussion.

Note: Be sure to save your class list (e.g., by typing it into a Word file), as we will use it again in a later activity.

Journal Entry

Earth’s Nicknames

As you watch the video of our rotating Earth that opens this chapter, think about some of the nicknames you’ve heard for our planet, such as the Blue Marble, the Blue Planet, Spaceship Earth, a Pale Blue Dot. Which nickname is your favorite? Write a paragraph or two explaining your choice and why you think the nickname makes sense.

Show Teachers Notes

This journal entry will work best if you have students write it after doing the activity above, so that they have some context for choosing the nickname that they think best applies to our planet as viewed from space.

Activity

The Deep Space Climate Observatory

The rotating Earth video that opens this chapter is from a satellite called The Deep Space Climate Observatory (DSCOVR). This satellite was launched (in 2015) into a special orbit around the Sun, in which the satellite orbits at a position where the Sun’s gravity and Earth’s gravity balance out. This allows the satellite to remain in a position where it can always observe the daylight side of Earth from a distance of about 1.5 million kilometers away. Learn more about the satellite and its observations by doing the following and answering the accompanying questions:

  1. Watch the chapter opening video again. Explain how it shows the two different ways in which we’ve described Earth’s rotation in earlier chapters: (1) Earth rotates counterclockwise as viewed from above the North Pole. (2) Earth rotates from west to east.
  2. As you watch the video, which part of Earth is experiencing noon time? Which side of the Earth is experiencing dawn, and which side is experiencing sunset?
  3. Watch this video from DSCOVR that describes the mission and shows a time lapse of a full year on Earth.
    a. Freeze the video in December. How can you tell that it is winter for the Northern Hemisphere and summer for the Southern Hemisphere?
    b. Deserts are regions that have very little cloud cover. Can you identify any major desert regions of Earth?
  4. Visit this web page and watch the video in which the Moon passed in front of Earth as viewed by the DSCOVR satellite.
    a. Which side of the Moon are we seeing – the side that faces Earth or the side that faces away from Earth?
    b. What phase of the Moon (as viewed by people on Earth) was it when this video was taken, and how do you know?
  5. Visit this page, where you will find DSCOVR’s most recent views (as recently as 12 hours ago) of Earth. Find your location in these views, and comment on how what you see corresponds to the weather you have been experiencing.
Show Teachers Notes

This activity should be considered optional based on your available time. Its goals are two-fold: (1) to help students understand the video they’ve watched above; and (2) to get them thinking about the technology we use to study Earth, which is an important topic that we will return to many times throughout the rest of the book. Answers to the questions:

  1. (1) The counterclockwise rotation should be clear (assuming students understand the meaning of clockwise and counterclockwise). (2) The west to east rotation is easiest to see if you pick a point on the western side of a continent, then notice that it moves to the right – which is to the east – over the course of a day.
  2. Noon is along the line going vertically through the middle of the picture. It is dawn along the left, since that is where we see locations that are just emerging into daylight, and sunset along the right, since that is where we see locations that are just moving out of daylight and into night.
    • a. You can tell it is summer for the Southern Hemisphere because Antarctica is in continuous daylight.
    • b. The most obvious desert is over the wide band of northern Africa (the Sahara) and the Saudi peninsula. Students may also be able to notice the desert area of Australia fairly easily.
    • a. We are seeing the Moon’s far side, which is the side of the Moon that faces away from Earth; that is why it does not like the familiar full face of the Moon that we see from Earth.
    • b. It is new moon. One way to know this is from the fact that the far side is in daylight, which means the side facing Earth is entirely in night – which only occurs at new moon. Another way to know it is new moon is that the lighting tells you that the Moon is between the Sun and Earth, which the Moon’s position at new moon.
  5. Assuming the satellite is currently operating, the given page will provide a view of Earth from 12 to 36 hours earlier. Students should be able to find their approximate location and zoom in to see clouds in the area, and thereby connect the space view to the weather from the observed time period.

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