Billions of years ago, crushed quartz reacting with water could have created the conditions needed for the evolution of the photosynthetic microbes responsible for most of the oxygen now in Earths atmosphere
Earthquakes and other geological processes may have enabled oxygen-producing reactions that shaped the evolution of some of Earth’s earliest organisms.
Today, oxygen makes up around a fifth of Earth’s atmosphere, with most of it produced by plants and microbes. It didn’t start that way. There was very little oxygen in the atmosphere until levels spiked during the Great Oxidation Event between 2.4 billion and 2.3 billion years ago thanks to the rapid spread of microbes that release oxygen through photosynthesis.
|Quartz-lined cavity (Baker Ranch Agate Mine, Luna County, New Mexico, USA)|
Photo: James St. John
A team of geochemists from the Chinese Academy of Sciences, working with colleagues from the University of Hong Kong, Tianjin University and the University of California, has found evidence that suggests much of the oxygen in early Earth's early atmosphere may have come from rocks. In their study, reported in Proceedings of the National Academy of Sciences, the group conducted lab experiments involving crushing rocks, exposing the results to water and measuring reactive oxygen species that were emitted.
Prior research has shown that Earth experienced what has been called the Great Oxidation Event approximately 2.3 to 2.4 billion years ago. During this time, microbe numbers increased dramatically, as they released oxygen during photosynthesis.
But prior research has also suggested that a common life ancestor existed before the Great Oxidation Event, which further suggests that there was some amount of oxygen exposure. In this new effort, the researchers suggest that such oxygen could have come from rocks interacting with water.
The work involved crushing samples of quartz and then exposing them to water, which replicates some of the conditions that existed on early Earth prior to the rise of high levels of oxygen in the atmosphere. Adding water to freshly crushed quartz, the researchers found, led to reactions between the water and newly broken crystals.
This resulted it the formation of molecular oxygen along with other reactive oxygen species like hydrogen peroxide. Such species are also known as free radicals and they would have played an important role in the evolution of early life. This is because by damaging DNA and other cell components, the free radicals would have pressured early life to adapt.
The researchers suggest a variety of events could have led to the release of such materials, such as earthquakes, erosion or the movement of glaciers. They further suggest that similar processes could be happening on other planets right now—with Mars sandstorms, for example, or fluctuating tides on moons that have water. Such processes, they point out, could produce oxygen, which could be play a role in the development of life.
The above story is based on Materials provided by Proceedings of the National Academy of Sciences.