When we think about the five great extinctions that the Earth has suffered, we imagine catastrophes that wiped out a multitude of species almost at once. But researchers have used artificial intelligence to sort through millions of marine fossils and reconstruct how life changed over hundreds of millions of years.
The usual image of a mass extinction is that of a sudden disaster: something extraordinary happens and numerous living beings disappear. However, the fossil record does not function as a continuous movie. It preserves fragments of history, distributed among rocks of different ages and places. Furthermore, some species leave many traces, while others barely appear. Therefore, it is difficult to determine when exactly each decline began.
Let’s imagine that we only keep a few pages of a diary. If in the last one we have for a month a person is mentioned and in the first one for the following month they no longer appear, we lack data to know what happened between the two. With fossils, one of the challenges is to find out what part of this silence is due to the disappearance of the organisms and what part is due to the gaps in the collection.
The scale at which we observe changes also matters. On a graph spanning hundreds of millions of years, several successive dips can look like one. If we can better distinguish the ages of the finds, it is worth asking whether the declines occurred at the same time or if some preceded others.
The result is surprising: in three of those five crises, biodiversity appears to have declined for much longer periods.
This means that the loss of species could have spread over considerable intervals, rather than being concentrated in a single episode. To reconstruct these trends, we must compare the first and last known appearances of different organisms. But a last fossil appearance does not necessarily indicate the exact moment of their disappearance: perhaps they still lived in regions whose sediments we have not found.
Because? One possibility is that some species disappeared while others emerged, offsetting some of the losses.
For example, an ecosystem may lose certain organisms and gain others during a period of environmental change. The total number of species on a global scale may not plummet immediately, even if their composition is profoundly transformed. Thus, a prolonged crisis can hide stages of deterioration, replacement and recovery. It is also possible that different regions reacted at different times.
Let’s think of two seabeds with the same number of species. One can be populated by organisms very different from those of the other. If, over time, one ends up looking like the other, the count for each place can remain the same, even if some of the variety that existed between the two has been lost.
The question is whether the pattern holds when comparing regions and groups of organisms with different fossil records.
But be careful, that does not doubt that an asteroid caused a rapid extinction at the end of the Cretaceous. And there is an important caution: for now, these are preliminary results that need to be verified.
REFERENCES
James Dinneen. “Vast new fossil record challenges story of Earth’s «big five» mass extinctions”. NatureOctober 20, 2026.
Shuzhong Shen, Shuhan Zhang, Jiacheng Leng, Junxian Fan, and Douglas H. Erwin. “OneStrata: A foundation model for deep-time biodiversity and mass extinction reassessment.” Geological Society of America Abstracts with ProgramsOctober 12, 2026.
Jun-Xuan Fan, Shu-Zhong Shen, Douglas H. Erwin, Peter M. Sadler, Norman MacLeod et al. “A high-resolution summary of Cambrian to Early Triassic marine invertebrate biodiversity.” ScienceJanuary 17, 2020.
