GEOLOGICALLY ANCIENT DNA: FACT OR ARTEFACT?

How long can nucleic acids and cells survive in Earth's geosphere? This fundamental question that is not easy to answer. Studies continue to report ancient DNA sequences and viable microbial cells that are many millions of years old. Theoretical considerations and empirical studies suggest maximal DNA survival of fifty thousand to one million years. However, a series of publications claim that genetic material from plants, animals and microbes – and even viable bacterial cells – can survive in amber, halite, soft tissue and sediments for up to several hundred million years. However, ancient DNA studies involve a high risk of false-positive results and therefore bear a heavy burden of proof. We evaluate the foundations on which the claims of geologically ancient DNA depend and conclude that, although exciting, the reports suffer from inadequate experimental setup and insufficient authentication of results. As a consequence, it remains doubtful whether amplifiable DNA sequences and viable bacteria can survive over geological timescales. To enhance the credibility of future studies and to assist in discarding false-positive results, we propose a rigorous set of authentication criteria for work with geologically ancient DNA.