The Asteroid Darkness Had a Size Limit
A new ocean model reconstructs the first century after Chicxulub. In the dark, survival may have depended on how little energy a body needed.
The Extinction Filter
The asteroid that ended the Cretaceous did not erase ocean life evenly. Some plankton groups collapsed while smaller, flexible organisms crossed the boundary. The fossil pattern has been clear; the mechanism selecting survivors has not.
A 2026 Nature study modelled the first 100 years after the Chicxulub impact. Its result turns impact winter into a biological filter: prolonged darkness cut the ocean's energy supply, while body size helped determine which populations fell below a survivable threshold.
When sunlight vanished, every extra unit of body became a bill.
What the Model Did
The researchers used the EcoGENIE ecosystem model, coupling ocean circulation and chemistry to a plankton community divided by size and feeding strategy. Unlike models that allow a population to rebound from an arbitrarily tiny remnant, this one imposed extinction when biomass fell below the equivalent of a single individual in a size class.
- The simulated community included phytoplankton, zooplankton, mixotrophs and foraminifera.
- Larger organisms carried higher energy demands and higher extinction thresholds.
- Impact forcing reduced light and cooled the planet.
- The model reproduced several broad patterns observed in the marine fossil record.
Large zooplankton and planktic foraminifera were especially vulnerable. Small phytoplankton and mixotrophs — organisms able to combine photosynthesis with feeding — survived more readily, and high-latitude settings sometimes lost less diversity.
What's the Timeline?
The lethal transition began on ecological rather than geological time. Dust, soot and sulfur aerosols blocked sunlight after impact, cutting photosynthesis and cascading through food webs during the model's opening century. Recovery over later millennia does not soften that first bottleneck: extinction happens when a population reaches zero, not when the climate eventually improves.
This is a reconstruction of an event 66 million years ago, not a countdown to a modern impact. NASA currently reports no known asteroid posing a significant impact risk over the next century.
The Boundary of the Evidence
EcoGENIE deals in functional plankton types, not a perfect digital copy of every Cretaceous species. Extinction thresholds are model choices constrained by biological scaling, and the Northern Hemisphere high-latitude fossil record remains limited.
Still, the model connected three pieces that previously sat apart: atmospheric darkness, organism energy demands and the selective losses written in marine fossils. The asteroid struck once. Extinction arrived as a sequence of budgets that no longer balanced.