Australia: The Land Where Time Began

A biography of the Australian continent 

Continent Growth Linked to 2-step Rise of Atmospheric Oxygen

The presence of life on Earth has been allowed to evolve by the oxygen in the atmosphere, but it remains to be resolved how the presence of oxygen in the atmosphere evolved from an initially oxygen-free state. According to Lee et al. the rise of atmospheric oxygen occurred in 2 stages: during the Great Oxygenation Event between 2.5-2.0 Ga, and about 2.0 Gyr later during the Neoproterozoic Oxygenation Event. In this paper Lee et al. propose that the initiation of plate tectonics when the continents formed about 2.7-2.5 Ga may have led to oxygenation by the following mechanism. The first stage was the composition change of the Earth’s crust from mafic rocks, which are rich in iron and magnesium, to felsic rocks, that are rich in feldspar and quartz, that could have caused a decrease in the oxidative efficiency of the surface of the Earth thereby allowing atmospheric oxygen to rise. Over the next billion years carbon accumulated steadily on the continents, metamorphic and magmatic reactions within the growing continental carbon reservoir facilitated a gradual increase in total long-term input of CO₂ to the ocean-atmosphere system. As O₂ is produced during the burial of organic carbon, a second rise in O₂ may have been triggered by the increase in CO₂ input. Lee et al. suggest that a 2-step rise in atmospheric O₂ may therefore be a natural consequence of plate tectonics, the formation of continents and the growth of the crustal carbon reservoir.

Sources & Further reading

Lee, C.-T. A., L. Y. Yeung, N. R. McKenzie, Y. Yokoyama, K. Ozaki and A. Lenardic (2016). "Two-step rise of atmospheric oxygen linked to the growth of continents." Nature Geosci 9(6): 417-424.