Pop Quiz! How many species exist on Earth? Thousands? Millions? And what would you guess if we told you, 99.9% of the species on Earth haven't been discovered yet? Most of those species are microbial species such as bacteria, which are too small for us to see with the naked eye.

Have an answer now? Scientists think that Earth is home to nearly one trillion different species. This is, of course, an estimate.

Estimation Process

Scientists came up with it by pulling together data from sources such as the National Institutes of Health's Human Microbiome Project and the Earth Microbiome Project. These projects began when researchers realized they were probably dramatically underestimating biodiversity. After compiling all that data, scientists applied ecological models and new ecological rules for how biodiversity relates to abundance of organisms in a given area.

Scientists have catalogued fewer than ten million of these microbial species. And of those ten million, only about 10,000 have ever been grown in a lab, and fewer than 100,000 have had their genetic sequences classified.

Learn More

"Earth May Be Home to One Trillion Species," Science Daily

"Scaling laws predict global microbial diversity," Kenneth J. Loceya, and Jay T. Lennona. PNAS, 2016