For over 2 billion years, the Earth’s atmosphere was unable to form a stable ozone layer that shields complex life from harmful ultraviolet radiation. New research by Yale University and Michigan State University suggests that high levels of iodine in the oceans played a key role in delaying this process.
The study, published in PNAS, proposes a new theory on why the ozone layer didn’t develop until around 450 million years ago. Iodine, an essential nutrient for life, reacts with oxygen to form a molecule that destroys ozone in the atmosphere. This reaction would have prevented complex life from thriving on land, as the ozone layer is crucial for protecting it from UV radiation.
The research team analyzed geological evidence and developed an ocean-atmosphere model to reconstruct the iodine-ozone dynamics of early Earth. They found that elevated marine iodide content prevailed throughout most of Earth’s history, leading to significant inorganic iodine emissions into the atmosphere after oxygen levels rose. This would have disrupted ozone formation and potentially led to unstable and low ozone levels for half a billion years.
The study’s findings challenge the widely accepted theory that the establishment of a substantial concentration of atmospheric oxygen was the primary driver behind the creation of an ozone layer. Instead, the researchers suggest that the delayed stabilization of Earth’s ozone layer was caused by the battle between iodine and oxygen.
Source: https://astrobiology.com/2025/01/explaining-the-delayed-rise-of-plants-and-animals-on-land-iodine-and-oxygen.html