Fossils tell of the end of an ice age 300 million years ago
Study global warming in the past to understand climate change in the present. Throughout its long history, the Earth has experienced very different climatic conditions, alternating between glacial periods and periods of global warming, which have shaped the planet and influenced the evolution of organisms. Even before the appearance of the dinosaurs, one of the most extensive glaciations took place during the late Palaeozoic (about 300 million years ago) and ended with a warming phase that led to the almost complete disappearance of glaciers and polar ice caps, with major consequences for biodiversity.
An international team of scientists, including researchers from the Università Statale di Milano, Sapienza University of Rome and the University of St. Andrews in Scotland, studied the late Palaeozoic glaciation and its retreat, followed by a significant rise in temperatures, to better understand the current climate emergency.
The results of this study, published in the international journal Nature Geoscience, reconstruct atmospheric CO2 levels over a time span of 80 million years for the first time.
The atmosphere of the past is often studied through the analysis of small air bubbles embedded in the polar ice caps, thanks to which we are able to reconstruct climatic variations up to about 800,000 years ago accurately. However, the challenge faced by this study was to develop methodologies capable of going back between 340 and 260 million years. The focus was thus on brachiopod fossils, marine invertebrates with a shell made of calcium carbonate, which were very abundant during the Palaeozoic and are still represented by some living species. Analyses showed how CO2 levels were intimately linked to the evolution of glaciation and its end. The researchers measured low levels of carbon dioxide concomitant with the formation of extensive polar ice caps. Conversely, the increase in CO2, which was the product of intense volcanic activity, was contemporaneous with a global reduction in glaciers and an increase in the average surface temperature of the oceans by up to 4 degrees Celsius. And today, just as happened 300 million years ago, the warming of the atmosphere, caused by the increase in CO2 and methane gas, has triggered a noticeable reduction in glaciers and polar ice caps.
"Fossils and the geochemical characteristics of their remains are a valuable source of information that allows us to reconstruct the climate and environment in which these organisms lived, even in the distant past, and to compare this data with the changes that are taking place today," says Lucia Angiolini, a lecturer at the Ardito Desio Department of Earth Sciences at the Università Statale di Milano.
"As the organism grows, its shell expands and incorporates numerous elements and chemical compounds that form a kind of archive throughout its life cycle. It is indeed well known how shells are linked to the composition of seawater and the variation of several parameters, including temperature and acidity (pH)," points out Claudio Garbelli, lecturer at Sapienza University of Rome.
"Some of the elements present in the calcium carbonate of shells are determined by the pH values of seawater, which in turn depends on the amount of atmospheric CO2," adds Hana Jurikova, a researcher at the University of St. Andrews in Scotland and first author of the study. "By measuring some of the elements contained in fossil shells (such as boron and strontium, for example) and with the help of sophisticated mathematical models, we were able to reconstruct with some accuracy the amount of CO2 present in the atmosphere over a time span of 80 million years, between 340 and 260 million years ago," Jurikova concludes.
Studies such as this not only highlight the importance of fossils as repositories of useful information for understanding the dynamics of past climate and environmental changes but also provide an indispensable source of data for developing predictive models of current phenomena and their impact on biodiversity.
References:
Jurikova, H., Garbelli, C., Whiteford, R. et al. Rapid rise in atmospheric CO2 marked the end of the Late Palaeozoic Ice Age. Nat. Geosci. (2025). https://doi.org/10.1038/
Further Information:
Claudio Garbelli
Department of Earth Sciences