Billion years ago, the amount of free oxygen present in the atmosphere was minimal. It increased at an unprecedented rate of 10,000 times over 200 million years during the period called the Great Oxidation Event. During this stage, the chemical reactions and composition on Earth’s surface also changed completely.
How these two changes are linked to each other is the focus of investigation conducted by the University of British Columbia researchers Matthijs Smit and Klaus Mezger. They reviewed the geochemistry of more than 48,000 rocks dating back billions of years, consisting of various shales and igneous rock types from around the world.
“It turned out that a staggering change occurred in the composition of continents at the same time free oxygen was starting to accumulate in the oceans,” Smit said. The continents were initially composed of rocks rich in magnesium and low in silica, and more importantly, they contained a mineral called olivine. The olivine reacts with water by consuming the water’s oxygen.
The amount of olivine present significantly declined with the evolution of earth’s crust. Consequently, the water became saturated with oxygen, and free oxygen was able to escape and accumulate in the atmosphere.
“It really appears to have been the starting point for life diversification as we know it. After that change, the Earth became much more habitable and suitable for the evolution of complex life, but that needed some trigger mechanism, and that’s what we may have found,” Smit explained.
What triggered the evolution of earth’s crust is still a work in progress, although Smit hints that modern plate tectonics began at around the same period as the Great Oxidation event.