Earth could be home to nearly 1 trillion species, with only one-thousandth of 1 percent now identified, a U.S. study said Monday.
The estimate, published in the U.S. journal Proceedings of the National Academy of Sciences, was based on data representing more than 5.6 million microscopic and nonmicroscopic species from 35,000 locations across all the world's oceans and continents, except Antarctica.
"Estimating the number of species on Earth is among the great challenges in biology," lead author Jay Lennon, associate professor at the Indiana University, said in a statement. "Our study combines the largest available datasets with ecological models and new ecological rules for how biodiversity relates to abundance. This gave us a new and rigorous estimate for the number of microbial species on Earth."
Many earlier attempts, said Lennon, simply ignored microorganisms or were informed by older datasets that were based on biased techniques or questionable extrapolations.
The realization that microorganisms were significantly under-sampled caused an explosion in new microbial sampling efforts over the past several years, he said.
These efforts included the collection of human-related microorganisms by the U.S. National Institutes of Health's Human Microbiome Project; marine microorganisms by the Tara Oceans Expedition; and aquatic, terrestrial and host-related microorganisms by the Earth Microbiome Project.
These data sources and many others were compiled to create the inventory in the new study, which pulled together 20,376 sampling efforts on bacteria, archaea and microscopic fungi and 14,862 sampling efforts on communities of trees, birds and mammals.
The study's results also suggested that actually identifying every microbial species on Earth is an almost unimaginably huge challenge.
For example, the Earth Microbiome Project -- a global multidisciplinary project to identify microscope organisms -- has so far cataloged less than 10 million species.
"Of those cataloged species, only about 10,000 have ever been grown in a lab, and fewer than 100,000 have classified sequences," Lennon said. "Our results show that this leaves 100,000 times more microorganisms awaiting discovery -- and 100 million to be fully explored. Microbial biodiversity, it appears, is greater than ever imagined."
