Nonliving describes anything that isn't alive. Rocks, water, air, and sunlight are all nonliving things. They don't grow, breathe, eat, or reproduce like living things do.

Scientists use this word to distinguish between the living and nonliving parts of an ecosystem. In a forest, the trees, birds, and mushrooms are living things, while the soil, streams, and boulders are nonliving. Both types of things matter: plants need nonliving sunlight and water to survive, and animals need nonliving air to breathe.

Sometimes the line seems blurry. A wooden desk was once part of a living tree, but now it's nonliving because it can't grow or respond to its environment. A virus puzzles scientists because it has some characteristics of living things but can't reproduce on its own, leading some to consider it nonliving.

Understanding what makes something living or nonliving helps scientists study how different parts of nature work together. When you examine a drop of pond water under a microscope, you're discovering which tiny specks are living organisms and which are nonliving particles drifting in the water.