As you read this page, a jaguar is on the hunt in the Amazon rainforest, a coral reef teems with life, and a bike messenger in New York City is riding with a bagel in hand. These all might seem like unrelated events, but in fact, all living things have more in common than you think. For starters, we all live on planet Earth. Together, plants, animals, and people spin through outer space, protected only by a thin layer of atmosphere. Second, everything on Earth (And I mean everything! Your dog, car, spaghetti dinner, and even you!) is made up of atoms. Last, all living things—no matter how small or big, whether it is a plant turning sunlight into sugar or a person eating a sandwich—build their bodies and get energy from their food. Every living thing is dependent on the earth’s limited resources, and each other, for survival. To see just how much we are connected, we need to understand the earth’s ecosystems.