Researchers at Texas A&M University have identified a mechanism by which thymine, a key building block of DNA, may have helped early life survive on Earth. The findings, published in the Proceedings of the National Academy of Sciences, offer new insights into the origins of molecular evolution and how biological systems persisted under the extreme conditions of primordial Earth.
Dr. Peter Rentzepis, a professor in the Department of Electrical and Computer Engineering, led the study alongside research assistants Keyvan Khosh Abady and Negar Karpourazar. The team investigated a long-standing scientific puzzle: why thymine replaced uracil in DNA despite being more prone to ultraviolet (UV) damage.
On early Earth, the lack of a protective ozone layer exposed life to intense solar radiation, making the choice of thymine seem counterintuitive.
Using biophotonics, an interdisciplinary field employing light-based spectroscopic methods, the researchers compared thymine and uracil under controlled UV conditions designed to mimic the radiation environment of early Earth. They discovered that thymine directs UV damage into a more reversible form. This suggests that early genetic molecules survived intense sunlight not by avoiding damage, but by controlling it and facilitating self-repair.
“Thymine may have acted as a molecular sunscreen, absorbing harmful UV energy and keeping the damage confined to the genetic bases rather than allowing it to harm more vulnerable parts of the molecule,” said Khosh Abady.
