Every breath that every animal and person around the world takes may seem like a simple task, but it is actually a quiet collaboration with the planet that has been in existence for billions of years. The oxygen we inhale—this colorless, odorless gas—is the very life force of the planet.
And, yet, oxygen is not the most abundant gas on the planet. In fact, nitrogen comprises about 78% of the Earth’s atmosphere. So why do almost all lifeforms need oxygen to live? The answer has to do with our biological history, and how our planet evolved over an incredibly long time.
Oxygen is the fuel to our cells and the key element that sustains entire ecosystems around the globe. Click through this gallery to see how it became such an important part of life on Earth.