Instructions:
Read the text below. This is obviously a terrible way to present this text for a reader. With a
small group you will decide what text features should be added to make this text easier to
understand. You must give this text a title – and 2 subheadings. Decide what words you would
put in boldface. What pictures, diagrams, charts, graphs, and sidebars/textboxes would you
use? On a larger piece of paper you will set up a rough design for your text, that shows were all
text features will be located.
You saw in Chapter 5 that early scholars imagined a universe made of four basic
“elements”: air, water, earth, and fire. We now know that fire refers only to the
energy given off by burning, so it is not made of matter. Air, water and earth are
made of matter, but they are not elements in the scientific sense. In this section,
you will look more closely at these three substances to see what chemical
elements each contains.
The term atmosphere usually refers to a gaseous envelope surrounding a planet.
Nitrogen, oxygen, argon, and carbon dioxide are part of the composition that
makes up Earth’s atmosphere.
Three of these gases go through interesting cycles that are essential to life on
our planet. A cycle is a “return trip” for a substance. It goes through a sequence
of steps or processes and then comes back to its starting point. You may also
remember these cycles from your earlier science studies.
Oxygen is so reactive that it cannot exist for more than a fleeting instant as an
uncombined atom. The oxygen in the atmosphere is therefore in the form of
diatomic O2 molecules. Nearly all living cells depend on oxygen to release
energy through cell respiration.
The nitrogen gas in the atmosphere consists of N2 molecules. This element is
vital to life. Every protein in your body contains nitrogen atoms that cycled
through the atmosphere at some time.
Gaseous argon consists of single, uncombined Ar atoms. Argon is unreactive
and is not involved in a cycle.
The carbon in our atmosphere is present in carbon dioxide (CO2) molecules,
which also contain the element oxygen. Plants and plant-like organisms use CO2
to make the food we depend on and then release O2 back to the atmosphere.
Dry air does not contain any hydrogen at all. However, air is seldom truly dry. It
contains a variable percentage of water vapour – more on a hot humid day above
a lake, less above a desert. Thus air does contain the element hydrogen in H 2O
molecules. These molecules are cycled back and forth between the atmosphere
and Earth.
Earth is sometimes called “the big blue marble” because water dominates its
surface. Even land that seems dry may have water lying or flowing beneath it.
Much of what appears to be land in Canada’s North is actually “sea ice”: solid
water floating on the Arctic Ocean. Together, all of this water makes up the
hydrosphere, a nearly continuous layer of water lying on or just under Earth’s
crust.