An estimated 99.9% of all species that have ever lived on Earth are now extinct, according to the American Museum of Natural History. That means the millions of species alive today represent a tiny sliver of everything that has existed over the past 3.5 billion years of life on this planet. Extinction is, in the broadest sense, the norm rather than the exception.
Why 99.9% Have Disappeared
Life on Earth has been churning through species for billions of years. Most go extinct not in dramatic catastrophes but through a slow, steady process sometimes called background extinction. Under normal conditions, roughly 0.1 to 2 species per million go extinct each year. Over geological time, that quiet drumbeat adds up. Species evolve, thrive for a while, then get outcompeted, lose their food sources, or fail to adapt to shifting climates. The 99.9% figure reflects this deep accumulation of loss across all of Earth’s history.
Scientists can only estimate this number because the fossil record is incomplete. Most organisms never fossilize at all, especially soft-bodied creatures, insects, and deep-sea life. The true number of species that have ever existed is unknowable, but the proportion that survived to the present is vanishingly small no matter how you calculate it.
The Five Mass Extinctions
Layered on top of background extinction are five catastrophic events that wiped out enormous percentages of life in geologically short windows. The worst was the end-Permian extinction around 252 million years ago, sometimes called “the Great Dying.” Estimates of species-level losses range from 81% to as high as 96%, depending on the method used to extrapolate from the fossil record. At the genus level (the taxonomic rank above species), between 56% and 69% of all genera vanished.
The most famous mass extinction, the one that killed the non-avian dinosaurs 66 million years ago, was severe but not the largest. A recent reassessment suggests the end-Permian may be the only one of the Big Five that clearly crossed the 75% species-loss threshold, a benchmark sometimes used to define a mass extinction. The others were devastating in their own right but may fall slightly below that line when species-level losses are recalculated from genus-level data.
How Many Species Exist Today
One of the challenges in understanding modern extinction is that we don’t know how many species are alive right now. The most widely cited estimate puts the total at about 8.75 million living species, but roughly 80% of those are hypothetical. Only about 1.2 million have been formally described by science, including around 950,000 animals. Estimates for the true total range wildly, from 2 million to as high as 3 trillion when microorganisms are included.
This gap matters. Species can go extinct before they’re ever discovered. When scientists talk about modern extinction rates, they’re working with an incomplete picture, particularly for insects, fungi, and deep-ocean organisms that remain largely uncatalogued.
What’s Threatened Right Now
Of the species scientists have formally evaluated, 28% are currently threatened with extinction. That translates to more than 48,600 species on the IUCN Red List facing some level of extinction risk. But the threat isn’t distributed evenly across the tree of life.
- Cycads (ancient palm-like plants): 71% threatened
- Reef-forming corals: 44% threatened
- Amphibians: 41% threatened
- Sharks, rays, and chimeras: 38% threatened
- Trees: 38% threatened
- Mammals: 27% threatened
- Reptiles: 21% threatened
- Birds: 11.5% threatened
Amphibians stand out as especially vulnerable because they breathe through their skin, making them acutely sensitive to pollution, habitat changes, and a devastating fungal disease that has spread across continents. Corals face a similarly dire outlook as ocean temperatures rise and acidification intensifies.
Modern Extinction Rates Compared to the Past
The rate at which species are disappearing today is up to 100 times higher than the natural background rate, even using conservative assumptions designed to minimize the apparent severity. A study published in Science Advances calculated that the vertebrate species lost in the last century alone would have taken between 800 and 10,000 years to disappear under normal background conditions, depending on the group.
That comparison uses a background rate of 2 mammal extinctions per 10,000 species per 100 years, which is already twice as high as previous standard estimates. In other words, researchers deliberately set a high bar for “normal” extinction and still found modern losses far exceeding it.
Marine vs. Land Species
Recorded extinctions in the ocean are about 9 times lower than on land, with only 19 to 24 documented marine extinctions out of more than 850 total. But this gap is partly an artifact of how little we’ve studied ocean life. Only about 3% of marine species have been formally assessed for extinction risk, compared to 4% of land species. When researchers look at the best-studied groups in both realms, the picture converges: between 20% and 25% of species are threatened regardless of whether they live on land or in the sea.
What’s Driving Modern Extinctions
Habitat loss is the primary driver. When forests are cleared, wetlands drained, or grasslands converted to agriculture, the species that depend on those ecosystems lose their ability to survive. This single factor outweighs all others in pushing species toward extinction.
Beyond habitat loss, the major threats include overexploitation of wildlife for commercial purposes (hunting, fishing, and the wildlife trade), the introduction of invasive species that outcompete or prey on native ones, pollution, and the spread of diseases. Climate change acts as a threat multiplier, reshaping habitats faster than many species can adapt or migrate.
Projections for the Coming Decades
Climate models suggest the extinction picture will worsen considerably depending on how much the planet warms. Under current international emissions commitments, which project roughly a 4.9°F (2.7°C) rise in global temperature, about 1 in 20 species worldwide would face extinction risk. If emissions continue at current trends and temperatures rise by 9.7°F (5.4°C), close to one-third of all species, roughly 30%, could be at risk by the end of this century.
Those numbers represent risk of extinction, not guaranteed loss. Some species at risk will survive through conservation efforts, range shifts, or adaptation. But the projections underscore that the percentage of extinct species, already 99.9% of everything that has ever lived, is set to grow measurably within a single human lifetime.