The U.S. has spent several billion dollars looking for life on other planets. Shouldn't we spend at least that much finding and identifying life on Earth?

That is the argument behind a taxonomy analysis by a trio of scientists in Science, published on January 25. They argue just $500 million to $1 billion a year could ensure that all species were described and catalogued within 50 years. New tools will help too: the genetic "barcode of life" ensures that a species description is appropriate while expert-driven Catalogue of Life and an ambitious effort to inventory more than 200,000 marine species are succeeding. The Internet and smartphones are also aiding the cause.

Since the turn of the century, 17,500 species have been officially described per year—and the rate is increasing (largely because more people are looking from different parts of the world than previously).

There's a lot of duplication, however. By the researchers own count, at least 20 percent of the 1.9 million species known to science are in fact not species at all, but "synonyms"—in other words, some species are named more than once. That brings the number down to 1.5 million identified species.

So what's left? It’s hard to know how many species have gone unidentified. Based on an average of expert guesses, surveys and the like, these researchers suggest there are somewhere between 2 and 8 million species of animals, plants, microbes and fungi on the planet (some previous estimates went as high as 100 million.) That means if present trends of identification continue, the job of surveying all life could be done as soon as 2040.

The authors also argue for opening the field even wider to amateurs, as has been done for birds, butterflies, flowers, fish and mammals. For example, a one-month survey in New Caledonia gathered 127,652 specimens encompassing 2,738 species of mollusk—eight out of 10 of which were previously unknown. And that's just mollusks. Think of the insects or, for that matter, archaea—the newest and possibly oldest domain of life. Of course, engaging the citizen scientist in searching for, say, nematodes, a microscopic worm, among other uncharismatic microfauna, will be challenging to say the least.

The catalog of known species is already tilted in favor of popular species. Although species are "as fundamental to biology as elements are to chemistry," the search for species is uniquely susceptible to popularity. There are a lot more bird species than nematodes at present and, as a result, there are probably 10 times more vertebrate zoologists, say, than botanists or scientists specializing in the diverse array of invertebrates. That's the exact opposite of how the numbers work for the planet's biodiversity. Of course, with the challenges of climate change, habitat loss and other human impacts in the Anthropocene, the real goal may not be to know all species but to ensure that as many of them as possible survive.