UNLIKE OTHER PLANETS in the solar system, Earth is a lush, beautiful world where all sorts of living things are able to thrive. More than 70 percent of the surface is covered with water—sparkling blue oceans and thousands of rivers, lakes, and streams. There are forests with vast canopies of green that stretch for miles, and millions of acres of fertile land. Beneath Earth's crust lie huge reserves of fossil fuels, including coal, crude oil, and natural gas, all of which formed millions of years ago. Also buried within the earth are generous stores of gold, silver, platinum, and diamonds, as well as numerous other valuable minerals.

Because Earth has existed for billions of years, some people think of it as a robust planet whose resources are infinite—a planet that has the ability to heal itself, no matter what humans do. But astronaut Michael Collins...