Determining how many millions of years ago dinosaur fossils were preserved can often be challenging. Although layers of sedimentary rock symbolize distinct eras of geologic history, accurately dating these layers or the fossils entombed within has been a persistent issue.
Dating fossilized bones and teeth has seen sporadic success, often hinging on the condition of the specimens. Both the fossilization process and the transformation of sediment into rock can change bones in ways that affect dating accuracy. While uranium-lead dating ranks among the most popular methods for dating materials, its application to directly dating fossils remains in the early stages.
However, dinosaur eggshells might provide a breakthrough in dating both fossils and the rocks that surround them. A team led by paleontologist Ryan Tucker from Stellenbosch University has innovated a method for dating eggshells, showing when they were encased in what initially may have been sand, mud, or other sediments. This timeframe can determine the burial period of other fossils within the same rock layer.
“If validated, this approach could greatly expand the range of continental sedimentary successions amenable to radioisotopic dating,” Tucker stated in a research study recently published in Nature Communications Earth & Environment.
This Goes Way Back
Vertebrates have been laying hard-shelled eggs for hundreds of millions of years, though the earliest dinosaur eggs had soft shells. The distinctive microstructure of calcium carbonate in fossil eggshells is particularly helpful for deducing the age of other fossils. These microstructures register a record of the diagenetic changes, which are the physical and chemical shifts during fossilization. Such changes can include water damage, breaks, and fractures from compression between sediment layers. This makes it easier to identify these indicators when estimating their age.