When dinosaur fossils are uncovered at a location, it is often not possible to tell how many millions of years ago their bones were buried. While different layers of sedimentary rock represent periods of geologic history frozen in time, their precise determination or the fossils trapped within them has often proven frustrating.
Fossil bones and teeth have been dated before with some success, but that success is inconsistent and depends on the specimens. Both fossilization and the process of sediment turning into rock can alter the bone in ways that interfere with accuracy. While uranium-lead dating is one of the most widely used methods for dating material, it is an emerging technique applied directly to dating fossils.
Dinosaur eggshells have finally found a way to explore nearby rocks and fossils. Led by paleontologist Ryan Tucker of Stellenbosch University, a team of researchers has devised a method of dating eggshells to reveal how long ago they were covered by sand, clay or other sediment. That information will tell the time of burial of any other fossils embedded in the same layer of rock.
“If validated, this approach could significantly expand the range of continental sedimentary successions amenable to radioisotopic dating,” Tucker said in a study recently published in Nature Communications Earth & Environment.
it goes back a long way
Vertebrates have been laying calcified eggs for hundreds of millions of years (although earlier dinosaur eggs had soft shells). What makes fossil eggshells so useful for determining the age of other fossils is the unique microscopic structure of the calcium carbonate found in them. The way its crystals are arranged captures a record of diagenetic changes, or physical and chemical changes, that occurred during fossilization. These can include water damage as well as wear and cracks caused by sediment accumulation between layers. This makes it easier to examine these signs when trying to determine how old they are.
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