Geological time, generally considered as a system of eras, periods and epochs materialized in rock strata, might actually follow a simple and unifying model. Indeed, a new study led by physicist Shaun Lovejoy from McGill University shows that the divisions marking the most important historical events, such as mass extinctions and major climate changes, follow a fractal pattern - meaning self-similar and statistically consistent across scales ranging from millions to hundreds of millions of years.
This discovery could have major implications for how scientists reconstruct the distant past and anticipate Earth's future.
"These divisions are the steps we use to calculate the time scale of virtually all the data we have about the ancient past," explains the physicist. "However, if we don't account for how these divisions cluster in time, we introduce biases into our understanding of past climate, ecosystems, and planetary changes."
The study, published in Earth and Planetary Science Letters, presents an analysis of regional and global geological time scales, including the internationally recognized Geological Time Scale (GTS2020). The team quantified the chronology of events marking the most recent 541 million years, known as the Phanerozoic eon. They found that their distribution was not only hierarchical in a qualitative sense, but also fractal in a quantitative sense, meaning that no single characteristic time scale alone defines the intervals between these major events.
"There are these numerous eras, epochs, periods and eons, but in reality, there is no characteristic time," explains Shaun Lovejoy. "We discovered that these major geological divisions can be explained by a kind of symmetry: scale symmetry in time."
"The most exciting aspect of this model is that geological time divisions, despite having different proximal causes, obey the same scaling law," explains Andrej Spiridonov, co-author of the study and professor at the Department of Geology and Mineralogy at Vilnius University.
A new conception of climate events and historical extinctions The team built a statistical model to simulate how these landmark events accumulate over time. The model shows that although events don't appear to follow any particular rule, they follow a more general hierarchical clustering pattern. This observation helps explain why certain intervals in geological sections show high event density, while others contain long periods of inactivity.
The results also highlight two distinct phenomena that researchers call "Sadler" effects. The first, already known, is the resolution effect: sections are less complete at finer time scales. The second, uncovered by the present study, is the length effect: at longer time intervals, sections become distorted. In other words, not only do older rock strata have more "missing pieces," but the way we divide time can introduce systematic biases.
"If you don't account for the fractal structure, your interpretation of changes over time will be biased," emphasizes Shaun Lovejoy. "This is particularly important for analyzing climate changes, biodiversity patterns, and extinction episodes from core samples."
The research team aims to improve dating methods and interpretation of paleoclimate and paleoenvironment from sections through better understanding of deep time structure. Next steps will involve refining the model and developing correction techniques that can be applied to large-scale geological datasets.
"There are keys in the knowledge of the past that can enable us to predict the future," he concludes.