Do we know all species that exist on earth? No, but perhaps we can make an estimation on the ammount of species that may possibly exist using taxonomy. From The Ladder of Nature via bestiaries to Linneas to understand worldwide biodiversity. How many organisms are out there? Estimations ranging between 3.000.000 and 100.000.000 species. Species discovery rates may help to make more accurate estimations. So far 1.200.000 species have been described. This may be as little as 10 percent of all existing species.
Video 4: How much biodiversity do we really know?