Capitol News

A recent study led by Yale University and contributed to by Michigan State University researcher Dalton Hardisty has shed light on the delayed rise of plants and animals on land. The study suggests that a prolonged "battle" between iodine and oxygen in Earth's early atmosphere postponed the formation of a stable ozone layer, crucial for protecting complex life from ultraviolet radiation.

"This was a fun interdisciplinary team that really challenged what we thought we knew about the establishment of Earth’s atmospheric ozone layer, which has wide-ranging implications," said Hardisty, an assistant professor in MSU's Department of Earth and Environmental Sciences. He highlighted his group's work on marine iodine cycling as vital to understanding ancient ozone models.

The study addresses why land plants did not appear until 450 million years ago, despite cyanobacteria existing for 2.7 billion years. Similarly, no fossils of complex land animals or plants exist before the Cambrian era (541 to 485 million years ago). Jingjun Liu, a Yale doctoral student and lead author of the study, emphasized that "the origin and diversification of complex life on Earth remains one of the most profound and enduring questions in natural science."

Researchers propose that elevated marine iodine concentrations hindered the stabilization of Earth's ozone layer. This disruption occurred despite sufficient atmospheric oxygen levels necessary for ozone production.

"We challenge this paradigm by considering how Earth’s evolving iodine cycle may have influenced ozone abundance and stability," Liu explained.

Hardisty's team analyzed geological evidence and developed an ocean-atmosphere model to explore early Earth's iodine-ozone dynamics. Their findings indicate high marine iodide content throughout much of Earth's history could have disrupted ozone formation following oxygen's rise.

The mechanism resembles how chlorofluorocarbons (CFCs) once created an "ozone hole" over Antarctica through photolysis releasing reactive chlorine. On a global scale, unstable low ozone levels likely persisted from 2.4 billion years ago until around half a billion years ago.