Scientists found a hidden clock inside dinosaur eggshells

The research was led by Dr. Ryan Tucker of Stellenbosch University's Department of Earth Sciences and published in the journal Communications Earth & Environment.

Why Fossil Dating Has Been So Difficult

Many fossil sites around the world lack precise age estimates. When scientists do not know exactly when fossils formed, it becomes much harder to understand how ancient species and ecosystems evolved and interacted over time. Traditional dating methods usually rely on minerals like zircon or apatite found near fossils, but these minerals are not consistently available at every site. Efforts to directly date fossil remains such as bones or teeth have often resulted in unreliable or inconsistent ages.

Instead of focusing on surrounding minerals or skeletal remains, Dr. Tucker and his colleagues turned their attention to fossilized dinosaur eggshells. Using advanced uranium-lead (U-Pb) dating combined with detailed elemental mapping, the team measured extremely small amounts of uranium and lead locked inside the calcite structure of the eggshells. These radioactive elements decay at known rates, effectively acting as a built-in clock that reveals when the eggs were buried.

Testing the Method in Utah and Mongolia

The researchers tested their approach on dinosaur eggshells from Utah (USA) and the Gobi Desert (Mongolia). The results showed that the eggshells could be dated with an accuracy of about five percent when compared with ages determined from volcanic ash layers. In Mongolia, the team achieved a major milestone by establishing the first direct age for a famous site containing dinosaur eggs and nests, placing it at roughly 75 million years old.

"Eggshell calcite is remarkably versatile," says Dr. Tucker. "It gives us a new way to date fossil sites where volcanic layers are missing, a challenge that has limited paleontology for decades."

The project brought together scientists from the North Carolina Museum of Natural Sciences, North Carolina State University, Colorado School of Mines, the Mongolian Academy of Sciences' Institute of Paleontology, and Universidade Federal de Ouro Preto (Brazil). Fieldwork in Mongolia was conducted through the Mongolian Alliance for Dinosaur Exploration (MADEx), with support from the National Geographic Society and the National Science Foundation.

A Powerful Tool for Understanding Dinosaur Evolution

By demonstrating that dinosaur eggshells can reliably record geologic time, the study creates a new connection between biology and Earth science and provides researchers with a valuable tool for dating fossil sites worldwide.

"Direct dating of fossils is a paleontologist's dream," says study co-author Lindsay Zanno, associate research professor at North Carolina State University and head of paleontology at the North Carolina Museum of Natural Sciences. "Armed with this new technique, we can unravel mysteries about dinosaur evolution that used to be insurmountable."

The article "U-Pb calcite age dating of fossil eggshell as an accurate deep time geochronometer" was published in Communications Earth & Environment.