Estimating the total number of different species in the biosphere is challenging due to the vast number of undiscovered organisms and the complexities of defining and classifying species. However, scientists estimate that there are approximately 8.7 million species on Earth, which includes both described and undocumented species. Of these, about 80% are believed to be still undescribed, particularly among microorganisms, fungi, and insects.
Currently, around 1.7 million species have been formally described and documented, primarily consisting of plants, animals, and fungi. The number is continually changing as new species are discovered and taxonomic classifications are revised.
It's important to note that biodiversity is not only about the number of species but also about the variety of ecosystems and genetic diversity within those species.