Mass extinction? Man may still have time to catalog Earth's species.

A trio of respected biologists and zoologists concludes that Earth's sixth mass extinction may be unfolding slower than feared, giving time for the valuable work of cataloging the planet's species.

For years, ecologists and biologists have warned that the planet is sliding into a mass extinction event comparable to the one that did in the dinosaurs 65 million years ago.

But Earth’s species may not be vanishing as fast as previously believed – providing a fresh opportunity to catalog and conserve more of them before global warming and habitat loss take a higher toll on the planet’s biodiversity.

That's the conclusion a trio of respected biologists and zoologists has reached after reviewing recent studies on extinction, the pace at which new species are being reported, estimates of undiscovered species, and the human and technological capital available for building the catalog.

When it comes to discovering and preserving biodiversity, "things aren't hopeless," says Mark Costello, a University of Auckland marine zoologist and the lead author of the analysis, which appeared in this week’s issue of Science.

Three years ago, another, larger team of biologists and zoologists estimated that if collectively countries devoted $500 million to $1 billion a year to the project of cataloging nonbacterial life on Earth, the project could be complete within 50 years.

Dr. Costello and colleagues renew that call. And their lower estimate of the number of species and a higher estimate of the people available than many thought implies the job could be done more quickly.

The stakes are high, many researchers say. Human population growth and activities – from altering landscapes and oceans to altering climate – are widely seen as the drivers behind the current mass-extinction event, the planet’s sixth.

"We are the asteroid," says Michael Novacek, provost and curator at the American Museum of Natural History in New York, referring to the event widely held to have triggered the demise of the dinosaurs 65 million years ago.

"This may be the most important century in our evolutionary history, where the environment is really transformed to a level where the nature of life on Earth is redefined," says Dr. Novacek, who was not part of the team performing the new analysis.

Getting a handle on the full range of nonbacterial species the planet hosts is important for a number of reasons, researchers say. A full listing of what lives where would provide important information for maintaining the health of ecosystems on which humans rely for food, clean water, and other so-called ecosystem services. And undiscovered species could represent new sources of compounds for pharmaceuticals or appear as novel structures human engineers could mimic for lighter, stronger materials.

At its broadest, the widespread loss of biodiversity before anyone has a chance to take the full measure of what's out there makes it difficult to fully grasp the ecological consequences of its loss.

Novacek and others say they are a bit surprised at the relatively low number of nonbacterial species the team estimates as living on the planet – about half the 10 million that others estimate as realistic. And the trio's estimate for a global extinction rate – less than 1 percent per decade – is far below the worst-case scenario of 5 percent per decade some have estimated.

Still, Costello and colleagues acknowledge that if extinction rates are on the high side, say 5 percent per decade, half the 5 million nonbacterial species he and his colleagues estimate as currently inhabiting Earth will have vanished within 150 years.

The analysis, co-written by Oxford University zoologist Robert May and Nigle Stork at Griffith University in Australia, draws on several recent studies to suggest that cataloging species before they vanish may be more tractable than many believe.

Better scientific housekeeping – settling on one scientific name for an organism (many creatures often had several) has helped lower the estimate of known species from about 1.9 million to 1.5 million, Costello says. Improvements in the methods for estimating Earth's biodiversity have narrowed the range of extant nonbacterial species from between 30 million and 100 million to perhaps 2 million to 8 million, with the team's best estimate at 5 million.

Meanwhile, the pace of discovery has been picking up. Over the past 10 years, an average of 17,500 new species have been described each year, a rate that has reached 18,000 a year since 2006.

It has been difficult to determine the overall global extinction rate for nonbacterial organisms. Some vertebrates have been disappearing at rates comparable to previous mass extinctions, the team notes. But conservation efforts, habitats that may be degraded or fragmented, but not destroyed, and the adaptability of some organisms to farmland or human-managed forests, could well be slowing the planet's overall pace of extinctions, the team suggests.

For all the efforts to improve estimates of the planet's overall species count, that number remains highly uncertain, cautions Andrew Hamilton, a biologist and executive director of academic innovation at the University of Houston.

"The fact of the matter is we don't know, even within an order of magnitude, how many species there are on the planet," he says.

In the end, however, the numbers may be less important than the analysis's overall message that while formidable, the cataloging task is attainable within a reasonable period of time, given money and creative ways to enlist more hands and eyes to the task, Dr. Hamilton says.

For instance, with the range of technologies available – from vast online data bases to smart phones that can take a high-resolution picture; stamp it with date, time, and a GPS location; then upload it to a central repository – the discovery effort can enlist dedicated amateurs for some aspects, researchers say.

One popular approach is known as a BioBlitz – a 24-hour assault on a particular patch of land by professionals and volunteers to record as many organisms as possible in that location.

The American Museum of Natural History's Novacek recalls a BioBlitz the museum and other groups sponsored in Central Park in 2003. More than 800 species were identified in the trees, on the ground, and in ponds, with participants discovering a new species of centipede, Novacek says.

The effort represents nothing less than planetary exploration, Hamilton suggests.

"If we organize our workforce efficiently and we treat this like a mission to a little-known planet," it's possible to assemble the catalog of nonbacterial organisms within a generation, Hamilton says.