Just when we humans thought we knew a thing or two about our home planet, Mother Earth made sure to remind us we've barely scratched the surface.
A new study has found that this magnificent blue ball may still be hiding up to a mind-blowing 1 trillion species -- roughly 135 species for every man, woman and child alive today.
If the findings are true, they mean we humans have yet to unearth 99.999 percent of all species.
"Microbial biodiversity, it appears, is greater than we ever imagined," Jay T. Lennon, an associate professor of biology at Indiana University Bloomington, said in a press release.
Lennon and his colleague Ken Locey combed through databases from numerous government, academic and citizen science sources for their study, published this week in the journal Proceedings of the National Academy of Sciences. They compiled a list of over 5.6 million species -- from the largest mammals to the smallest single-celled microbes -- from 35,000 locations around the globe.
According to the study, "tests of biodiversity theory rarely include both microbial and macrobial datasets." As a result, biodiversity understanding is typically limited to the more "conspicuous species of plants and animals."
But by including the microbial data, the team was able to uncover how rare or common host microbiomes are. They could then use "scaling laws," a common toolset in the scientific community, to predict diversity as biological traits scale up, eventually reaching an estimate of how many species exist on the entire planet.
The task, Lennon said, is "among the great challenges in biology"
(Story continues below.)
To put the team's findings in perspective, a 2011 study predicted that globally, there are 8.7 million eukaryotic species -- organisms with a complex cell or cells, including animals, plants and fungi -- while the Earth Microbiome Project has cataloged less than 10 million species of microbial life.
Which is all to say, we're still a long way from 1 trillion. But while identifying every microbial species on Earth would be an "almost unimaginably huge challenge," according to the authors, we have to start somewhere -- for life's sake.
“Just like mapping the Milky Way and other galaxies helps us understand and appreciate our place in the universe and its history, understanding the immense diversity of microbial life helps us understand and appreciate our place in the evolution of life on Earth,” Locey told IFLScience.
And sweet Mother Earth always has a few more tricks up her sleeve.