We are in what scientists call the sixth mass extinction, a wave of species loss driven not by asteroids or volcanic eruptions but by human activity. The term has been used in scientific literature since the mid-1990s, and the current rate of species extinction is estimated to be 1,000 times higher than the natural background rate. Some projections suggest future rates could reach 10,000 times higher.
The Big Five Extinctions Before Ours
Earth has experienced five previous mass extinctions over the last half-billion years, each wiping out a significant portion of life. They set the baseline for what “mass extinction” means: at minimum, 75% or more of species lost within a geologically short window of about 2 million years.
The End Ordovician extinction, roughly 444 million years ago, was triggered by rapid glaciation on the southern supercontinent Gondwana. The Late Devonian extinction, about 372 million years ago, has no single confirmed cause, though suspects include global cooling, volcanic activity, and ocean oxygen depletion from algal blooms. The End Permian extinction, approximately 252 million years ago, was the worst of all. Massive volcanic eruptions in Siberia are thought to have set it off, killing an estimated 90% of marine species and roughly 70% of land vertebrates.
The End Triassic extinction, about 200 million years ago, coincided with the breakup of the supercontinent Pangaea and the opening of the Atlantic Ocean. And the End Cretaceous extinction, 66 million years ago, is the most famous: an asteroid impact in what is now Mexico’s Yucatán Peninsula plunged Earth into darkness and ended the reign of non-bird dinosaurs.
Every one of those events was driven by a massive physical disruption, whether ice sheets, volcanoes, tectonic shifts, or an asteroid. What makes the current extinction fundamentally different is its cause: us.
Why This One Is Called the Sixth
The term “sixth mass extinction” places today’s biodiversity crisis in direct lineage with those five catastrophic events. Not all scientists agree the label fits perfectly. One common definition of mass extinction requires that 75% of species disappear within 2 million years, and we haven’t reached that threshold yet. Some researchers prefer the term “diversity crisis” or “biological annihilation” to describe what’s happening, arguing that the word “extinction” alone doesn’t capture the scale of population collapse occurring even among species that haven’t vanished entirely.
Still, the core facts are not in serious dispute. Earth is experiencing a human-driven ecological crisis with extinction rates far above anything that would occur naturally. Whether we’ve technically crossed the formal threshold of a “mass extinction” or are accelerating toward it is partly a question of definitions, but the trajectory is clear.
How Fast Species Are Disappearing
The natural background rate of extinction, the pace at which species would disappear without any unusual disruption, is relatively slow. Current extinction rates are roughly 1,000 times that baseline. More than 48,600 species are now threatened with extinction according to the IUCN Red List, representing 28% of all species that have been formally assessed.
Population declines paint an even starker picture than outright extinction counts. The Living Planet Index, tracked by the World Wildlife Fund, found a 73% average decline in monitored vertebrate wildlife populations (mammals, birds, amphibians, reptiles, and fish) between 1970 and 2020. That’s not 73% of species gone. It means that among the populations scientists track, the average group has shrunk by nearly three-quarters in just 50 years.
Which Groups Are Hit Hardest
Amphibians are among the most vulnerable animals on the planet right now. About 41% of all amphibian species are globally threatened, up from roughly 38% in 1980. The Neotropics, home to 48% of the world’s amphibians, has seen the steepest declines. Frogs, salamanders, and their relatives face a combination of habitat destruction, climate change, and a devastating fungal disease that has spread across continents.
On land, extinction is currently outpacing what’s happening in the ocean. Terrestrial vertebrates appear to have a lower tolerance for global warming events than marine animals. That said, marine species are not safe. Ocean creatures show higher sensitivity to temperature changes within their habitats, and threats like pollution, overfishing, and ocean acidification continue to intensify. The difference is that land-based species are currently losing habitat faster, largely because of agriculture and urban expansion.
What’s Driving It
Five major forces are behind the current crisis, and they all trace back to human activity.
- Land and sea use change: This is the single biggest driver. Converting forests, wetlands, and other natural habitats into farmland and cities destroys the ecosystems species depend on. Agricultural expansion remains the leading cause of deforestation worldwide.
- Overexploitation: The unsustainable harvest of wild plants and animals for food, fuel, and income threatens roughly one million species globally and undermines the livelihoods of billions of people who depend on those resources.
- Climate change: Greenhouse gas emissions have doubled since 1980, raising average global temperatures by at least 0.7°C. As many as one in six species could be threatened by climate-driven temperature increases alone.
- Pollution: Chemical and waste pollution has especially devastating effects on freshwater and marine habitats, poisoning ecosystems from the inside.
- Invasive species: Non-native species introduced by human activity have contributed to nearly 40% of all known animal extinctions since the 1600s.
These drivers don’t operate in isolation. A forest fragment surrounded by farmland becomes more vulnerable to invasive species, pollution runoff, and rising temperatures all at once. The compounding effect is what makes the current crisis so difficult to reverse with any single intervention.
How It Compares to Past Extinctions
The previous five mass extinctions unfolded over tens of thousands to millions of years. The current crisis is happening on a timescale of centuries, possibly decades, for certain groups. That speed is unusual even by mass extinction standards.
There’s another important distinction. Past extinctions were caused by physical processes, volcanic eruptions, ice ages, asteroid impacts, that organisms had no way to anticipate or prevent. The sixth extinction is caused by choices, which means it could theoretically be slowed or partially reversed through deliberate action. Initiatives like the “30 by 30” conservation target, which aims to protect 30% of land and coastal waters by 2030, represent one approach. California, for example, has already conserved about 22% of its coastal waters under this framework.
Whether the current crisis ultimately reaches the severity of events like the End Permian extinction depends largely on what happens in the next several decades. Predictions based solely on temperature trends are unreliable because the causes of today’s extinction, habitat destruction, pollution, overexploitation, differ fundamentally from the geological forces behind ancient events. The variables are more numerous and, at least in theory, more controllable.