When could life on Earth have emerged at all? An international research team addressed this fundamental question in a new study. The project was directed by Prof. Dr. Stephen Mojzsis from the Bavarian Research Institute of Experimental Geochemistry and Geophysics (BGI) at the University of Bayreuth.
The study focuses on the so-called RNA World hypothesis. According to this idea, RNA molecules were capable of both storing genetic information and replicating themselves long before the emergence of modern DNA. Using a three-dimensional computer model, the researchers were able to narrow down the period during which conditions on the early Earth first became favourable for long-lasting prebiotic processes, namely chemical processes that occurred before the emergence of the first life forms. In the study, the research team simulated the thermal evolution of the Earth's crust between 4.5 and 3.5 billion years ago. In addition to RNA, the team also considered other molecules relevant to life.
The calculations show that, until around 4.4 billion years ago, regular asteroid and meteorite impacts shaped the Earth during its early development. Such impacts repeatedly caused extreme heating of the Earth's surface and upper crust, potentially preventing the formation of complex organic molecules. Only afterwards did conditions gradually become more stable. The study's findings suggest that a particularly favourable window (a temporal „Sweet Spot“) for the development of RNA opened around 4.33 billion years ago.
At the same time, as so-called global sterilisation events caused by asteroid and meteorite impacts became less frequent, energy-rich hydrothermal systems may have become more widespread. These are environments in which hot water circulates through rock, providing large amounts of chemical energy. Such hydrothermal systems are regarded as possible cradles of early biochemical processes.
“Our study also suggests that life may have developed relatively rapidly once environmental conditions allowed it to do so,” says Professor Mojzsis. “The identified window is only around 130 million years earlier than the estimated emergence of the last universal common ancestor of all living organisms today.”
However, the researchers stress that their model cannot determine when life actually emerged. Rather, it identifies the period during which the thermal conditions required for long-term stable prebiotic chemistry on Earth were most likely present.
