This is a question that has not been answered, and it may never be known. There are estimates of the total number of species that reach as high as 100 million. What biologists do know is there are a lot more species we do not know about than the ones we have found and named. So far scientists have only discovered and named around two million species. This is why there are so many scientists exploring our world looking for undiscovered life.
You Can Be Part of the Adventure
The job is not a small one as you can see from the graphs below. There are millions of living things that need to be found and given a name. There are places where biologists are in a race against time and disappearing habitat. Even places like city parks and possibly your back yard could be home to a new species.
Taking a closer look you can see how the search is going for Chordates.
There is even more work to be done with the invertebrates which include the world of insecta.
One of the best ways to learn about how to become a species hunter is to find a local group hosting a BioBlitz. These are 24 - 48 hour events where scientists and volunteers try to find and list all the living things in a given area. There are also special days each year when biologists and volunteers try to count all the birds, or butterflies they see in one day. These events are a perfect way to learn about living things and meet some of the people that are looking for new life every day.
Graph data from: Biodiversity: Australian Biological Resources Study. 2nd Edition. September 2009. Retrieved May 22, 2010 from https://www.environment.gov.au/science/abrs/publications/other/numbers-l....
Ruth Kearns. (2010, May 21). How Many Species Are There?. ASU - Ask A Biologist. Retrieved from https://askabiologist.asu.edu/species-graphs
Ruth Kearns. "How Many Species Are There?". ASU - Ask A Biologist. 21 May, 2010. https://askabiologist.asu.edu/species-graphs
Ruth Kearns. "How Many Species Are There?". ASU - Ask A Biologist. 21 May 2010. ASU - Ask A Biologist, Web. . https://askabiologist.asu.edu/species-graphs
The amazing X-ray fish, or X-ray tetra (Pristella maxillaris). This chordate has a see-through body so you can look at its backbone.