Scientists have discovered over a million different species of living things on Earth, but they estimate there could be as many as nine million in total. That means there are millions of species still to be discovered. All over the world, even in the most difficult and extreme environments, we find life. The life on Earth is hugely varied, from the mold growing on your food, to human beings, to mushrooms in the woods. Scientists have devised a way of classifying these organisms, not only to organize them, but also to highlight similarities and differences.