Of all the species that have populated Earth at some time over the past 3.5 billion years, more than 95% have vanished — many of them in spectacular die-offs called mass extinctions. On that much, researchers can generally agree. Yet when it comes to taking stock of how much life exists today — and how quickly it will vanish in the future — uncertainty prevails.
Studies that try to tally the number of species of animals, plants and fungi alive right now produce estimates that swing from less than 2 million to more than 50 million. The problem is that researchers have so far sampled only a sliver of Earth’s biodiversity, and most of the unknown groups inhabit small regions of the world, often in habitats that are rapidly being destroyed.