Chapter 13

Earth’s Fresh Water

13.1 Water on Earth

Lesson Objectives

• Describe how water is distributed on Earth.


• Describe what powers the water cycle and how water moves through this cycle.

Introduction

Water is a simple compound, made of two atoms of hydrogen and one atom of oxygen
bonded together. More than any other substance on the Earth, water is important to life
and has remarkable properties. Without water, life could probably not even exist on Earth.
When looking at Earth from space, the abundance of water on Earth becomes obvious —
seeFigure13.1. On land, water is also common: it swirls and meanders through streams,
falls from the sky, freezes into snow flakes, and even makes up most of you and me. In this
chapter, we’ll look at the distribution of water on Earth, and also examine some of its unique
properties.

Distribution of Earth’s Water

AsFigure13.1makes clear, water is the most abundant substance on the Earth’s surface.
About 71% of the Earth’s surface is covered with water, most of which is found in the oceans.
In fact, 97% of Earth’s water, nearly all of it, is in the Earth’s oceans. This means that just
3% of Earth’s water isfresh water, water with low concentrations of salts (Figure13.2).
Most freshwater is found as ice in the vast glaciers of Greenland and the immense ice sheets
of Antarctica. That leaves just 0.6% of Earth’s water that is freshwater that humans can