Human: In the new Planet Earth II Documentary film, how many species of animals are there on Earth? Assistant: 
The number of species on Earth is estimated to be between 5 and 30 million. It is hard to estimate the exact number of species on Earth because it is difficult to determine whether two different species are the same or different. For example, two different species of birds can look very similar to each other, but if we examine their DNA, we might find that they are not the same species. The number of species on Earth is constantly changing as new species are discovered, and some species go extinct.