Ancient DNA Research Faces Reality Check: Limits to Recovering Cretaceous-Era Genetic material
Recent attempts to extract DNA from fossils dating back to the Cretaceous Period-between 145 and 66 million years ago-have yielded genetic material not from dinosaurs or their contemporaries, but from much younger bacteria. This discovery underscores the fundamental limitations of DNA preservation and dashes hopes of readily unlocking the genetic secrets of life from deep time.
While the popular creativity, fueled by fiction like Jurassic Park, envisions retrieving intact DNA from ancient organisms, scientific research reveals a far more constrained timeline for genetic survival. A 2012 study, co-authored by paleogeneticist Michael Gilbert, modeled the decay rate of DNA, finding its “half-life”-the time it takes for half of the DNA bonds to break-is approximately 521 years. This means even under ideal conditions, complete DNA degradation is certain over geological timescales.
Gilbert’s team analyzed mitochondrial DNA from 158 bones of extinct moa birds in New Zealand, previously dated using carbon dating methods, to determine this decay rate. Their model predicts a maximum survival of around 6.8 million years for DNA, far short of the tens of millions of years required for Cretaceous-era recovery.
“The best conditions for preserving ancient DNA are cool, dark, dry, and relatively recent,” explains Jennifer Raff, a biological anthropologist at the University of Kansas. “Permafrost is usually the best place to find well-preserved DNA.” The bacterial DNA recently found in Cretaceous fossils likely originated from more recent contamination, highlighting the challenges of distinguishing ancient genetic material from modern intrusions.
This research clarifies the boundaries of ancient DNA analysis, focusing future efforts on more recent fossils and refining techniques to minimize contamination and accurately interpret fragmented genetic data.