A joint team of Professor Yusuke Yokoyama of the Atmosphere and Ocean Research Institute of the University of Tokyo (others, Rice University and Yale University in the United States) reveals a close causal relationship between the growth of the continental crust and the gradual rise in atmospheric oxygen concentration. Announced that it was done.He made full use of the integrated interpretation of geoscientific information and the carbon cycle model for the Earth's surface sphere.
Unlike other planets, the surface of the earth today is rich in free oxygen.The ultimate cause is the production of oxygen by photosynthetic organisms, but that alone cannot explain it.There are two major periods of rising oxygen concentration in Earth's history.The Great Oxidation Event (GOE) about 2 to 25 billion years ago and the Neoproterozoic Oxidation Event (NOE) about 20 to 7 million years ago.However, the reason why these two rising periods occurred and the mechanism were unknown.
The research team reinterpreted the uranium-lead dating results of a mineral called zircon (ZrSiO4) and carried out petrological considerations.As a result of the large amount of water supplied to the inside of the earth due to the subduction of the plate, it was found that the composition of the continental crust changed from mafic to felsic about 27 to 25 billion years ago.Mafic rocks rich in iron and magnesium have a stronger effect of removing oxygen from the atmosphere than felsic rocks rich in silicic acid. The occurrence of GOE is attributed to the drastic decrease in atmospheric oxygen consumption due to the formation of the felsic continental crust.
In addition, after the establishment of plate tectonics, carbon in the Earth's surface layer was deposited on the continental crust as carbonates and organic matter.As a result, it was clarified by a mathematical model that the second increase in oxygen concentration (NOE) occurred. NOE is said to be associated with the emergence of diverse fauna (the emergence of the Ediacaran fauna and the Cambrian explosion).
This research is said to be a presentation of a new view of the earth.The planetary-scale ultra-long-term biogeochemical cycle that accompanies plate tectonics has created a planet rich in oxygen and harbors higher organisms.
