There are approximately 8.7 million species on Earth according to the International Union for Conservation of Nature (IUCN) and a widely cited 2011 scientific estimate. However, only about 1.2 million species have been scientifically described and cataloged so far, meaning that the vast majority of species are still undiscovered or undescribed. Some recent estimates range from about 5 million to over 100 million species, and some even hypothesize up to 1 trillion species including microscopic life. Nonetheless, the figure of around 8.7 million species is commonly referenced as a comprehensive estimate for eukaryotic life on Earth today.