For nearly all of human history, fewer than a million people populated Earth at any one time. Today our population has grown beyond 7 billion people, shows just how recently and suddenly this monumental change has taken place. For every one person who used to exist more than 10,000 years ago, several thousand people exist today!

We rely on the ecosystem services that natural systems provide. For example, forested hillsides help people living below by purifying water and air, cycling nutrients, regulating water flow, preventing flooding, and reducing erosion, as well as by providing game, wildlife, timber, recreation, and aesthetic beauty. The global human population increased after the agricultural revolution and then skyrocketed as a result of the industrial revolution.

Note that the tear in the graph represents the passage of time and a change in x-axis values. Data compiled from U.S. Census Bureau, U.N. Population Division, and other sources. For every person alive in the year 1800, about how many people are alive today? Each DATA Q in this book asks you to examine the figure carefully so that you understand what it is showing. Once you take the time to understand what it shows, the rest is a breeze!


Because this is the first DATA Q of our book, let’s walk through it together.