Are We in Earth’s Next Mass Extinction? What Scientists Say

In September 1914, a bird named Martha died at the Cincinnati Zoo. She was the last passenger pigeon. A century earlier, this species had numbered in the billions, and flocks reportedly darkened the sky for hours as they passed overhead. Within a few human lifetimes, hunting and forest clearing took the species from one of the most abundant birds on Earth to a single animal in a cage.

Martha’s story is often told as a tragedy about one species. Some scientists now ask a bigger question: is it an early chapter in a much larger story? Life on Earth has been through mass extinctions before, five of them, each wiping out a large share of all living species. Researchers disagree about whether we are in the opening stages of a sixth. Most agree the current loss of species is far faster than normal.

This article covers what mass extinctions are, what caused the earlier ones, what the evidence says about today, and where scientists disagree.

What Counts as a Mass Extinction?

Extinction is normal. Over Earth’s history, the vast majority of species that ever lived have died out. Under ordinary conditions, species disappear at a slow, steady “background rate,” while new ones evolve to replace them.

A mass extinction is different. In a widely cited 2011 paper in Nature, Anthony Barnosky and colleagues used a working definition: the loss of roughly three-quarters of all species within a geologically short time, which they put at under about two million years. Two million years sounds long to us, but in geological terms it is a blink.

By that standard, Earth has gone through five. Some researchers note that scientists chose the word “mass” loosely, and the threshold isn’t a hard line in nature. It is a yardstick that lets us compare events across hundreds of millions of years.

The Big Five

Paleontologists identify these five events from the fossil record, mostly using marine animals, which fossilize well.

The percentages are estimates, and they vary between studies. Fossil data is patchy, and nobody counted species back then. Still, the broad picture is consistent.

The Great Dying

The end-Permian event, about 252 million years ago, was the worst. Estimates suggest more than 90% of marine species and a large share of land species disappeared. The main suspect is the Siberian Traps, an enormous outpouring of lava across what is now Russia, which released vast quantities of carbon dioxide and other gases. The result was a hot, acidified, oxygen-starved ocean.

Dating work published in 2014 in the Proceedings of the National Academy of Sciences by Seth Burgess and colleagues suggested the main extinction pulse lasted roughly 60,000 years, give or take. That is fast for geology. It is very slow compared with a human lifetime.

The Asteroid

The most famous event is the last one. In 1980, a team led by physicist Luis Alvarez and geologist Walter Alvarez proposed that an asteroid struck Earth about 66 million years ago, based on an unusual layer of iridium in rock around the world. The impact site, the Chicxulub crater near Mexico’s Yucatán Peninsula, was later identified. A 2010 review of the evidence by a panel of scientists in Science concluded the impact was the main driver of the end-Cretaceous extinction, which ended the reign of the non-avian dinosaurs.

The takeaway is that earlier mass extinctions were driven by forces much larger than any one species: volcanoes, asteroids, and swings in climate and ocean chemistry.

What Is Happening Now?

This time, the cause is a single species, ours. Here is what the evidence shows.

Extinction rates are well above normal

A 2015 study in Science Advances by Gerardo Ceballos and colleagues, “Accelerated modern human-induced species losses”, compared recent vertebrate extinctions with the background rate. Even using conservative assumptions, they found the average rate of vertebrate loss over the past century was about 100 times higher than normal. At the background rate, the number of vertebrate species lost since 1900 would have taken somewhere between 800 and 10,000 years to disappear.

A million species at risk

In 2019, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) published a global assessment drawing on thousands of studies. It estimated about 8 million animal and plant species on Earth, with around 1 million threatened with extinction, many within decades unless the pressures on them ease. The IUCN Red List, which tracks the status of species worldwide, now lists tens of thousands of species as threatened, and its numbers rise with each update. Check the site for the latest count.

The IPBES report ranked the main causes. In order of global impact, they are changes in land and sea use (mostly farming and development), direct exploitation such as hunting and fishing, climate change, pollution, and invasive species.

Wild animal populations are shrinking

Extinction is the last step. Before it comes decline. The Living Planet Index, run by the Zoological Society of London and used in WWF’s reports, tracks monitored wildlife populations. The 2024 edition reported an average decline of 73% in monitored vertebrate populations since 1970. That doesn’t mean 73% of animals are gone. It’s an average of changes across thousands of tracked populations, and it is a measure of trend, not total numbers. But the direction is consistent and worrying.

The planet’s animal makeup has shifted

A 2018 study by Yinon Bar-On, Rob Phillips, and Ron Milo in PNAS estimated the biomass of life on Earth. Among mammals, livestock accounted for around 60% of the total mass, humans about 36%, and wild mammals only about 4%. It is an odd statistic to sit with. Most of the large mammal life on Earth is now something we raise for food.

Coral reefs are in trouble

Reefs hold a disproportionate share of marine biodiversity, and they are especially vulnerable to heat. Since 2023, the world has experienced a major global coral bleaching event, which NOAA’s Coral Reef Watch reported as affecting a large majority of the world’s reef area at some point. Bleaching doesn’t always kill coral, but repeated events give reefs little time to recover.

Recent, well-documented losses

Some individual cases are well documented:

• The golden toad of Costa Rica’s Monteverde cloud forest was last seen in 1989.
• The baiji, or Yangtze River dolphin, was declared functionally extinct after a 2006 survey found none.
• The Bramble Cay melomys, a small rodent on an island off Australia, was declared extinct in 2016, and is often cited as the first mammal lost mainly to human-caused climate change.
• In 2023, the U.S. Fish and Wildlife Service delisted 21 species because they had gone extinct, including the ivory-billed woodpecker.
• The last male northern white rhino, Sudan, died in 2018. Only two females remain, so the subspecies’ survival depends on assisted reproduction.

Are We in a Mass Extinction Yet? Scientists Disagree

This is where honesty matters. Researchers don’t all agree on the label.

The case that it has started. Ceballos, Paul Ehrlich, and Peter Raven argued in a 2020 PNAS paper that the loss of vertebrate populations and species represents a “biological annihilation” that signals a sixth mass extinction under way. In this view, waiting until three-quarters of species are gone before naming the problem means waiting until it’s too late to act.

The case for caution. Barnosky’s 2011 analysis took a more measured line. Looking at the fossil record, it concluded that we have not yet lost anything close to 75% of species. But it also found that if all species currently listed as threatened were lost, and current trends continued, a mass extinction could be reached in as little as a few centuries, or could take up to a couple of thousand years. Put another way, the loss has begun, but the “mass extinction” threshold hasn’t been crossed. Whether that distinction is comforting depends on your view.

The measurement problem. Counting extinctions is hard. Scientists have formally described only a fraction of the world’s species, so many could vanish before anyone knows they existed. Others argue some estimates of future loss are too high, because species can persist at tiny numbers for a long time. This “extinction debt,” where a species is doomed but hasn’t yet died, makes timing hard to pin down.

So the fairest summary: nearly everyone who studies this agrees that current extinction rates are far above normal and driven by humans. They differ on how to label it, and on how fast and how far it will go.

How Today Differs From the Past

Three differences stand out.

The cause. Earlier events came from volcanoes, an asteroid, and natural climate swings. Today’s pressures come from one species changing land, seas, and the atmosphere.

The speed. Some earlier events took tens of thousands of years or more. Researchers have estimated that carbon is being released into the atmosphere today at a rate roughly ten times faster than during the Paleocene-Eocene Thermal Maximum, a warming episode about 56 million years ago. That event caused big changes to ocean life, though it isn’t counted among the Big Five. The comparison is a reminder that pace matters, because species need time to move or adapt.

The fact that we can see it. No dinosaur ever read a Red List. We can measure what is happening, understand the causes, and act on them, which makes this unlike any previous extinction in Earth’s history.

What the Past Says About Recovery

Life has always bounced back. But “bounced back” is on a timescale that should give anyone pause.

After mass extinctions, biodiversity typically takes millions of years to rebuild, and the result is a different world. The end-Cretaceous event cleared the way for mammals to diversify, eventually leading to us. That is a remarkable outcome, but nobody alive would have been around to enjoy it. If current losses worsen into a true mass extinction, the planet would recover, in the sense that life would continue. It is the species we know and depend on that wouldn’t.

That is also why many scientists frame the issue around human wellbeing, not just wildlife. Pollinators, healthy soils, fisheries, forests, and clean water all depend on living systems that are losing diversity.

What Can Still Change

The picture isn’t hopeless, and the most responsible reading of the research includes the good news.

Conservation does work when it is funded and sustained. A 2021 analysis in Conservation Letters by Friederike Bolam and colleagues estimated that conservation efforts since the 1990s prevented roughly two to three dozen bird and mammal extinctions that would otherwise have happened. Species such as the California condor, humpback whale, and Mauritius kestrel have come back from very low numbers. Many countries have also agreed to the Kunming-Montreal Global Biodiversity Framework, adopted in 2022, which includes a target to protect 30% of land and sea by 2030. Whether those commitments are met is the real question.

The biggest drivers, habitat loss and climate change, are things societies can influence. The Montreal Protocol on ozone-depleting chemicals shows that coordinated global action on an environmental threat can work.

What Individuals Can Do

The scale of the problem is large, and individual choices won’t solve it alone. But some actions do matter, especially in aggregate:

• Support local habitat protection, whether through land trusts, wildlife groups, or voting on local land use.
• Reduce food waste and favor sustainably sourced seafood and farm products where you can.
• Plant native species and avoid pesticides in your own yard, which helps pollinators and birds.
• Take part in citizen science projects such as the Christmas Bird Count or iNaturalist, which supply real data to researchers.
• Stay skeptical of both doom and complacency. The honest picture is serious, but not settled.

The Bottom Line

So, are we living through the early stages of the sixth mass extinction? Some leading scientists say yes. Others say we are in a dangerous decline that could become one, but hasn’t yet. What both camps agree on is that species are disappearing much faster than they should be, that human activity is the cause, and that the next few decades will shape what comes after.

Martha the passenger pigeon couldn’t have changed her fate. We can still change ours.

Frequently Asked Questions

How many mass extinctions have there been?
Scientists recognize five major ones in the past 500 million years: the end-Ordovician, Late Devonian, end-Permian, end-Triassic, and end-Cretaceous events.

Are we in the sixth mass extinction right now?
Researchers disagree. Some say it has started. Others say current losses are alarming but haven’t yet reached the roughly 75% threshold used to define a mass extinction.

What is the biggest cause of species loss today?
According to the IPBES global assessment, changes in land and sea use, mainly agriculture, are the largest driver, followed by direct exploitation of species, climate change, pollution, and invasive species.

How long does it take life to recover from a mass extinction?
Typically millions of years.

Can extinction be reversed?
Not for species already gone. But conservation has pulled many species back from the brink, so the outcome for the ones still alive isn’t fixed.

Sources and Further Reading

• Barnosky et al., “Has the Earth’s sixth mass extinction already arrived?” Nature (2011)
• Ceballos et al., “Accelerated modern human-induced species losses,” Science Advances (2015)
• Ceballos, Ehrlich and Raven, “Vertebrates on the brink,” PNAS (2020)
• Bar-On, Phillips and Milo, “The biomass distribution on Earth,” PNAS (2018)
• IPBES Global Assessment on Biodiversity and Ecosystem Services (2019)
• IUCN Red List of Threatened Species
• Living Planet Index
• NOAA Coral Reef Watch
• Convention on Biological Diversity, Global Biodiversity Framework
• Extinction event, Wikipedia, a useful starting point for tracking original sources