Our planet is inhabited by nearly 10 million animal species. But what about life forms that are invisible to us? How many species of bacteria, archaea, protists, or other fungi inhabit the Earth? The answer: a lot. More than stars in our entire Galaxy.
Our galaxy is home to about 200 billion, but this number, as big as it is, it is nothing next to the 1000 billion species of microorganisms on earth. This is at least what suggests estimates made in 2016 by biologists from Indiana University (USA). If this is the case, we would only know one thousandth of 1% of all the species on the planet, despite all our efforts to document the catalog of life. While the understanding of microbial biodiversity has changed over the last decade (thanks to high-throughput sequencing and bioinformatics), there is still some way to go.
“Estimating the number of species on Earth is one of the biggest challenges in biology,” said Jay T. Lennon of Indiana University a few months ago and the lead author of the study. Researchers say they have identified as many as 5.6 million species from 35,000 different locations around the world. Models for predicting the development of biodiversity then made it possible to estimate the number of species at more than one trillion. We are not talking here about the number of micro-organisms, but about the number of species. The total number of living organisms on Earth – a nonillion (10 to the power of 30) would far exceed the total number of stars in the Universe.
To know the number of microbial species on Earth – besides satisfying our intrinsic curiosity – could indeed have beneficial implications for our species. The prospect of biodiversity still to be exploited could indeed stimulate the development of alternative fuels or drug treatments. Such discoveries may allow the development of new crops to feed our rapidly growing population, for example, in spite of land poverty.