radioactive dating

Dinosaur eggshells can reveal the age of other fossils

Biology, dinosaurs, evolution, paleontology, radioactive dating, Science / Shannon Garcia / February 21, 2026

When dinosaur fossils surface at a site, it is often not possible to tell how many millions of years ago their bones were buried. While the different strata of sedimentary rock represent periods of geologic history frozen in time, accurately dating them or the fossils trapped within them has frequently proven to be frustrating.

Fossilized bones and teeth have been dated with some success before, but that success is inconsistent and depends on the specimens. Both fossilization and the process of sediment turning to rock can alter the bone in ways that interfere with accuracy. While uranium-lead dating is among the most widely used methods for dating materials, it is just an emerging technology when applied to directly dating fossils.

Dinosaur eggshells might have finally cracked a way to date surrounding rocks and fossils. Led by paleontologist Ryan Tucker of Stellenbosch University, a team of researchers has devised a method of dating eggshells that reveals how long ago they were covered in what was once sand, mud, or other sediments. That information will give the burial time of any other fossils embedded in the same layer of rock.

“If validated, this approach could greatly expand the range of continental sedimentary successions amenable to radioisotopic dating,” Tucker said in a study recently published in Nature Communications Earth & Environment.

This goes way back

Vertebrates have been laying calcified eggs for hundreds of millions of years (although the first dinosaur eggs had soft shells). What makes fossil eggshells so useful for figuring out the age of other fossils is the unique microstructure of calcium carbonate found in them. The way its crystals are arranged capture a record of diagenetic changes, or physical and chemical changes that occurred during fossilization. These can include water damage, along with breaks and fissures caused by being compacted between layers of sediment. This makes it easier to screen for these signs when trying to determine how old they are.

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What did the snowball Earth look like?

All of which raises questions about what the snowball Earth might have looked like in the continental interiors. A team of US-based geologists think they’ve found some glacial deposits in the form of what are called the Tavakaiv sandstones in Colorado. These sandstones are found along the Front Range of the Rockies, including areas just west of Colorado Springs. And, if the authors’ interpretations are correct, they formed underneath a massive sheet of glacial ice.

There are lots of ways to form sandstone deposits, and they can be difficult to date because they’re aggregates of the remains of much older rocks. But in this case, the Tavakaiv sandstone is interrupted by intrusions of dark colored rock that contains quartz and large amounts of hematite, a form of iron oxide.

These intrusions tell us a remarkable number of things. For one, some process must have exerted enough force to drive material into small faults in the sandstone. Hematite only gets deposited under fairly specific conditions, which tells us a bit more. And, most critically, hematite can trap uranium and the lead it decays into, providing a way of dating when the deposits formed.

Under the snowball

Depending on which site was being sampled, the hematite produced a range of dates, from as recent as 660 million years ago to as old as 700 million years. That means all of them were formed during what’s termed the Sturtian glaciation, which ran from 715 million to 660 million years ago. At the time, the core of what is now North America was in the equatorial region. So, the Tavakaiv sandstones can provide a window into what at least one continent experienced during the most severe global glaciation of the Cryogenian Period.