How many species are there on Earth and in the Ocean? Short title: On the number of species on Earth and in the ocean

The diversity of life is one of the most striking aspects of our planet; hence knowing how many species inhabit Earth is among the most fundamental questions in science. Yet the answer to this question remains enigmatic because the limited sampling of the world’s biodiversity has precluded direct quantification, and because indirect estimations rely on assumptions that have proven highly controversial. Here we quantify the total number of species on Earth using a new described pattern. We show that the higher taxonomy of species (i.e. assignment of species to kingdom, class, order, family and genus) follows a consistent pattern from which the total number of species in any taxonomic group can be extrapolated. The approach was validated with well-known taxa and when applied to all domains of life it predicts ~8.9 million eukaryotic species globally of which ~2.2 million are marine. In spite of 250 years of taxonomic classification and over 1.2 million species already cataloged in a central database, our results suggest that some 86% of the species on Earth, and 91% in the ocean, still await description. With current rates of extinction now reaching 100 to 1000 times natural background rates, our slow advance in the description of species suggest that many species are likely to become extinct without us ever knowing they existed. Renewed interest in further exploration and taxonomy is critically required if this significant gap in our knowledge of life on Earth is to be breached.