New research has dispelled fears that millions of animal and plant species will be extinct before they are actually discovered.
Scientists from Auckland University, Queensland's Griffith University and England's Oxford University have narrowed down the number of species on earth to between two million and eight million - of which 1.5 million have already been discovered and named.
Earlier estimates of the number of species have been as high as 100 million. In 2011 the PLoS Biology journal published an analysis suggesting there are 8.7 million species, give or take 1.3 million.
Now Associate Professor Mark Costello of Auckland University and his colleagues put the top figure at eight million, in research published on Friday (NZ time) by Science magazine.
Their new estimate - and a previous erroneous belief that the number of taxonomists (people who describe and identify species) is declining - give new hope that new species can be recorded and then protected from extinction.
Scientists' estimates of species extinction rates have ranged up to five percent per decade.
"Over-estimates of the number of species on earth are self-defeating because they can make attempts to discover and conserve biodiversity appear to be hopeless," Dr Costello said.
"Our work suggests that this is far from the case. We believe that with just a modest increase in effort in taxonomy and conservation, most species could be discovered and protected from extinction."