Mass extinctions can make the present feel like a replay of deep time. The comparison is useful only when it is precise. The crisis at the Cretaceous–Paleogene boundary followed a sudden extraterrestrial impact, while the current decline of biodiversity is driven by multiple human activities. Both can disrupt food webs and remove species, but they are not the same kind of event.
What happened at the end of the Cretaceous?
About 66 million years ago, an asteroid struck the shallow sea near what is now the Yucatán Peninsula. The Chicxulub crater, shocked minerals, impact glass and a globally distributed boundary layer connect the impact to the extinction. The immediate effects varied by distance: thermal radiation, ejecta and seismic disturbance were followed by atmospheric dust and aerosols that reduced sunlight and disrupted photosynthesis. The collapse of primary production then travelled through marine and terrestrial food webs.
The event eliminated all non-avian dinosaurs, ammonites, pterosaurs and several marine reptile groups, among many other organisms. Birds are dinosaurs and a surviving branch of the group. The ecological losses were severe, but not every organism disappeared, and recovery unfolded unevenly among environments and lineages. The timing and contribution of Deccan Traps volcanism remain active research questions; volcanic emissions affected climate and ocean chemistry, but the impact is the clearest trigger at the boundary.
What is driving biodiversity change now?
Today’s pressures are cumulative rather than a single instantaneous blow. Global assessments identify changes in land and sea use, direct exploitation of organisms, climate change, pollution and invasive species among the leading direct drivers. Their relative importance differs by ecosystem and region, and they interact. Habitat conversion can isolate populations; harvesting can reduce them directly; warming can shift suitable conditions while pollution or invasive species add further stress.
The word Anthropocene is often used to describe human influence on Earth systems, but it has not been ratified as a formal epoch on the Geological Time Scale. That decision does not deny human impact. It distinguishes a widely used descriptive term from a formally defined chronostratigraphic unit.
Useful parallels, important differences
In both cases, losses in one part of a food web can affect organisms that depend on it. Fossils show that extinction reshapes communities rather than simply removing a list of species. Modern ecology likewise tracks changes in abundance, range, timing and interactions. These similarities help explain why biodiversity and ecosystem function matter.
The scale of time is different. Chicxulub produced a geologically abrupt shock, with its most destructive effects concentrated around the boundary. Current pressures are developing across decades and centuries, vary among regions, and arise from identifiable human decisions and systems. There is no sound basis for saying that nature is simply repeating the end-Cretaceous event, or that the same outcome is inevitable.
That difference changes what comparison is for. The fossil record shows that ecosystems can be transformed and that recovery does not restore the former community. It cannot predict an exact modern future. Present evidence can, however, identify pressures that people can reduce, habitats that can be protected and populations that need time and space to recover. Deep time supplies context; it does not replace current ecological evidence.
For the fossil sequence and biological turnover at the boundary, see the end of the Mesozoic and the overview of mass extinctions.
Frequently asked questions
Was the end-Cretaceous extinction caused by the same things affecting biodiversity today?
No. The boundary crisis is most strongly linked to the Chicxulub impact, while current biodiversity change has several human-driven causes, including habitat change, exploitation, climate change, pollution and invasive species.
Did Deccan Traps volcanism contribute to the end-Cretaceous crisis?
Volcanism preceded and overlapped the boundary and could have stressed climate and ecosystems. Researchers continue to evaluate its timing and relative contribution; it does not make the impact evidence disappear.
Is the Anthropocene an official geological epoch?
No. The proposal was rejected as a formal unit of the Geological Time Scale, although scientists and others continue to use the word to describe the extensive human influence on Earth.
Can the end-Cretaceous extinction predict what will happen now?
It documents how ecosystems respond to severe disruption, but it cannot provide a direct forecast. The causes and timescales today differ, and current human pressures can be changed.