Once upon a time, our atmosphere was a little thin on oxygen. Like, there wasn't any. Then, about three billion years ago, a handful of bacteria figured out how to harvest the energy from sunlight to make themselves some food. In the process, they consumed carbon dioxide, and gave off oxygen. So the air filled with oxygen, and all was right with the world. If you've ever taken an intro biology course, you've no doubt heard the tale. Photosynthetic bacteria are the heroes who brought oxygen to our planet. But maybe there's more to the story than that. Because in the online issue of Nature Geoscience, researchers from Australia say: the bacteria didn't act alone. The scientists looked at atmosphere oxygen levels throughout Earth's history. And they found that the amount of oxygen in the air spiked each time smaller land masses collided to form a supercontinent, like Pangea. These massive pile-ups generated mountain chains, and as the mountains eroded, they released nutrients into the oceans, feeding the photosynthetic bacteria. So the young Earth and its inhabitants worked together.