There are one trillion species on Earth – but how many of them do we know?

Humans are aiming to put a person on Mars. Probes are being designed to head to Alpha Centauri, our closest star. But new research shows that we know very little about the creatures that crawl around Earth. To be precise, humans only know about 1% of the one trillion species in existence.

The revelation comes from a team from Indiana University’s Bloomington College of Arts and Sciences. They took microbial, plant and animal datasets from government, academic and citizen science sources around the world and put them into one spreadsheet. Altogether, 5.6-million species from 35 000 places around the world were included.

They also used actual samples to get more complicated information about species. This included 20 000 bacteria and microscopic fungi samples, as well as 15 000 samples from trees, birds and mammals. Jay Lennon, an associate professor working on the project, said: “Our study combines the largest available datasets with ecological models and new ecological rules for how biodiversity relates to abundance.”

They then started applying scaling law to the data sets. This is a premise that the concentration of species in a known area can be multiplied by the total area of a place with unknown species to get a fairly accurate idea of how many species exist there. In this case, they looked at the whole planet.

Research two years ago found that one gram of soil can contain a billion organisms.

The team – publishing in the journal Proceedings of the National Academy of Sciences on May 2 – said their basic premise was that where there was space, there would be species. This led them to conclude that there are at least a trillion species alive on Earth today.

In the past scientists tended to count what they could see with the naked eye, or through microscopes. But microorganisms – or microbes – are invisible to the naked eye. Most of them are also single-celled. Given that they make up the majority of species, this means any previous count has been wildly undercounting life on Earth.

Genetic sequencing has started to fill the gaps in knowledge. This allows scientists to start estimating how many species are linked to the one they have sequenced. But even this cannot contend with the scale of uncatalogued species.

The Earth Microbiome Project – which is attempting to tally up all microorganisms – only counts species that it has physically documented. So far, it has 10-million species on its records. Of these, only 100 000 have had their genomes catalogues, and 10 000 have been grown in a lab.

Lennon said: “Our results show that this leaves 100-million [microbes] to be fully explored. Microbial diversity, it appears, is greater than ever imagined.”

The project is part of the National Science Foundation’s project to fill major gaps in humanity’s knowledge about the planet’s biodiversity. Simon Malcomber, director of the foundation’s Dimensions of Biodiversity programme, said: “This research highlights how much of that biodiversity still remains to be discovered and described.”