The alterations that humans are implementing on the planet are occurring over a few centuries, which may seem fast in geological terms. This rapid rate lies at the core of one of the most concerning discussions in contemporary biology: the possibility that another mass extinction is already commencing.
However, this time, the trigger may not be an asteroid or another natural calamity. The suggestion is that the initiators are us.
*We do not claim to be biologists, paleontologists, or climate scientists, and nothing stated here constitutes a conclusive judgment. This represents an overview of an ongoing scientific discourse, and the researchers mentioned hold differing opinions on significant aspects. Estimates regarding extinction across the entirety of the living world remain estimates, not established facts.*
## Defining mass extinction and why five
The term “mass extinction” is often used casually, yet paleontologists have a rather precise definition in mind. A mass extinction refers to the loss of more than three-quarters of Earth’s species within a relatively brief span of geological time.
By this criteria, it has transpired only five times in approximately the last 540 million years. The first, known as the Late Ordovician extinction around 445 million years ago, was associated with intense glaciation. The most catastrophic, the end-Permian “Great Dying” roughly 252 million years ago, obliterated an estimated 96 percent of marine species.
The Big Five were driven by natural phenomena with global repercussions: rapid climate shifts, massive volcanic eruptions, significant modifications in oceanic conditions and, 66 million years ago, the Chicxulub asteroid strike.
## How the sixth differs: no asteroid, no supervolcano, solely us
The notion that human actions could be instigating a sixth mass extinction gained prominence through Richard Leakey and Roger Lewin’s 1995 publication and subsequently, Elizabeth Kolbert’s Pulitzer Prize-winning *The Sixth Extinction*.
What distinguishes the current crisis is its catalyst. Human enterprises are altering the atmosphere, oceans, and terrestrial environments through habitat degradation, excessive wildlife exploitation, climate change, and ocean acidification.
It is beneficial to distinguish between two inquiries. Firstly: is there a significant, human-induced biodiversity crisis unfolding presently? There is widespread consensus on that. Secondly: have enough species already vanished for this to be recognized as a genuine “mass extinction”? That is where researchers diverge.
## The rate issue, and why speed is the entire narrative
A crucial element of the debate concerns not just the number of species that are vanishing, but the swiftness of their disappearance.
In a 2023 examination of 5,400 vertebrate genera, excluding fish, Ceballos and Ehrlich identified that 73 genera had become extinct since 1500. Absent human impacts, they estimated that those identical losses would have required about 18,000 years to unfold naturally. They approximated that vertebrate genera are currently disappearing at around 35 times the natural background rate observed over the past million years.
The authors are unequivocal about their interpretation. They assert: “Beyond any doubt, the human-driven sixth mass extinction is more severe than previously assessed and is rapidly accelerating.” This is a definitive statement, yet it is their interpretation rather than a neutral scientific agreement.
## Areas of scientific disagreement
Robert Cowie from the University of Hawaii and his team contend that the sixth extinction is already in progress, particularly when incorporating less-studied creatures like insects and snails. Their 2022 review estimated that Earth may have lost between 7.5 and 13 percent of its approximately two million recognized species since 1500.
Conversely, John Wiens and Kristen Saban adopt a more cautious perspective. In 2025, they posited that fewer than 0.1 percent of Earth’s known species have documented extinctions over the past 500 years.
A subsequent analysis of flora and fauna discovered 102 genera that had gone extinct since 1500. It concluded that recent extinctions of entire genera were uncommon, especially amongst birds, mammals, and island-dwelling species, and had not rapidly accelerated towards the present.
This does not imply that the biodiversity crisis is not genuine. Wiens and Saban themselves recognize human-induced extinctions and serious threats to species. Their argument is more specific: the losses cataloged so far may not yet warrant labeling the current crisis a “mass extinction.”
## Final reflections
The speed of extinction is significant because species do not uniformly respond to environmental changes. Some can evolve rapidly or relocate to new habitats, while others cannot.
Challenges arise when the climate or habitat transforms faster than a species can evolve or migrate to a suitable area. Research on responses to climate change suggests that climate variability can exceed species’ adaptive abilities, raising the extinction risk.
Our assessment is that the sixth mass extinction is not yet an established fact. Ceballos, Ehrlich, and Cowie argue that it is already underway, while Wiens and Saban maintain that the losses documented thus far do not reach the threshold for mass extinction classification.
What permits this potential sixth