The rise of Earth's continents may have tuned ancient oceans to just the right boron concentration for life to emerge, according to a new research study.
Earth's earliest continents may have set the chemical stage for life by regulating boron levels in ancient oceans, a new study in Terra Nova suggests.
Scientists have long proposed that boron helps stabilize the fragile sugars needed to build RNA-the molecule thought to have preceded DNA in early life-making it an essential ingredient in life's origins.
But boron operates within a narrow window: too much, and it becomes toxic to biological systems; too little, and it may never have contributed to life getting started.
"What we're talking about is a geological control system for Earth's surface chemistry," said Dr. Brendan Dyck, Associate Professor of Earth and Environmental Sciences in UBC Okanagan's Irving K. Barber Faculty of Science . "The growth of continents didn't just reshape the surface of the Earth-it may have helped set the chemical conditions that made life possible in the first place."
Dr. Dyck and collaborator Dr. Jon Wade from the University of Oxford found that before significant landmasses emerged more than 3.7 billion years ago, boron concentrations in Earth's early oceans were likely dangerously high. The rise of granite-rich continental crust, they argue, changed that.
The key was a boron-containing mineral called tourmaline, popularly known as a semi-precious stone that's also abundant in continental rock.
Tourmaline forms readily within granite-rich crust, locking boron away over geological time. As Earth's crust grew and weathered, boron was slowly and steadily released into surface waters, eventually stabilizing at concentrations close to those found in modern seawater.
This was within the range that, according to current scientific thinking, life can use.
That stabilization, the researchers suggest, may have been especially important on the early Earth, where without it, the fragile chemical building blocks of life would have broken down before they could combine into more complex structures.
The findings also raise questions about the search for life on other planets. Rocky planets lacking granite-rich continental crust, such as Mars, are unlikely to have surface waters with boron in a form life can use, suggesting that the geological evolution of a planet may be as important to habitability as its distance from the sun.
"This work reveals that the slow geological evolution of a planet's interior can meaningfully shape the surface environment in ways that may be critical for life."
