Date of Publication: 10 October 2023

One-Line Summary: The climate during the time of the dinosaurs* was not as warm as we thought it was.

Who did it: A team of researchers from Spain and the United Kingdom.

What did they study: They mapped and described sedimentary rocks from a lacustrine* environment that existed 130 million years ago, located in what is now Spain.

What they found: The researchers identified large rocks called “dropstones” in the layers of the sediments. Geologists believe that dropstones fall out of melting icebergs that have calved* from large glaciers. The researchers envisioned these large rocks settling into the sediment, as evidence of large ice-sheets on earth 130 million years ago.

Why does this matter: The Cretaceous* has long been thought to be a very warm period of Earth history, and devoid of polar ice caps. Because dropstones are made by large bodies of ice, they suggest that the Cretaceous was not always warm. This means that climate during the time of the dinosaurs was more complicated than we thought.

What next: Next steps are to see how widespread these glaciers were by searching for dropstones in the sedimentary rocks of the same age, but in other places on the globe.

Our take: We know that today, Earth’s climate has regions of both extreme cold as well as warmth. It’s not surprising that the Cretaceous climate, which represents nearly 80 million years of time, could have been geographically patchy in the same way. We need to start thinking about past climate as variable and dynamic.

*The basics: The time of the dinosaurs lasted for almost 200 million years: the sediments studied by the authors were near the halfway point of the dinosaurs’ time on Earth, in terms of age. Calving is what it’s called when huge pieces of ice split off from an ice sheet. Lacustrine refers to a lake, that is, the rocks that the authors analyzed were made from debris that had collected at the bottom of a lake. The Cretaceous is a period of Earth history extending from 145 to 66 million years ago; the age of the sediments investigated in this study (130 million years old) falls within this time period.

Who to talk to: Dr. Carlos L. Liesa, Departamento de Ciencias de la Tierra, Universidad de Zaragoza, Spain: carluis@unizar.es

The paper: Rodríguez-López, J.P., et al., 2023, Ice-rafted dropstones at midlatitudes in the Cretaceous of continental Iberia: Geology, https://doi.org/10.1130/G51725.1.

Journal page: https://watermark.silverchair.com/g51725.pdf

Keywords: Cretaceous, Spain, climate change, dropstones, glaciers, dinosaurs