WHERE DID OUR CELLS COME FROM?
One of the biggest events in the history of evolution was the development of mitochondria, the energy factories of all complex cells. Scientists think that they only evolved once, an event that completely changed the course of evolution. For billions of years, life was just single cells. It was impossible to make enough energy to form multicellular organisms like plants and animals. When oxygen appeared in the atmosphere, some cells learned how to use the new gas. In a chance event, one of these oxygen-breathing cells got inside a larger cell and started dividing. The two types of cell started to work together to make more energy than ever before. Over time, their relationship became permanent, and the oxygen-breathing cells became the mitochondria.