Key Idea 1
Which Atmospheric Gases Support Life?
Concept Question: Which atmospheric gases support life directly? Which gases support life by regulating the energy balance of our planet?

AtmosphereBegin this lesson by doing something that you do all the time—take a breath. Think for a moment. What did you just breathe into your lungs? What molecules were present in that breath of air? When you exhaled, were the same molecules still present? Or did the chemical content of the air change?

The molecules in your breath of air are representative of the gases present in Earth’s atmosphere. Atmospheric gases play many important roles on Earth and they are essential to your survival. For example, they allow you to obtain energy from food, they protect you from harmful radiation from the Sun and they regulate Earth's energy balance, providing a suitable climate for life.