The Mesoproterozoic Oxygenation Event

The accumulation of oxygen is one of the most important characteristics that distinguish Earth from other planets in the solar system,which is also considered to be the key factor influencing the birth and evolution of complex life forms.The oxygenation process of the Earth surface has long been viewed to be episodic with two critical intervals occurring in the early Paleoproterozoic(2.45-2.10 Ga)and the late Neoproterozoic(0.80-0.54 Ga),with a 1.3-billion-year-long low oxygen period in between.Recently,increasing independent works carried out by different scientific teams in the Yanliao Basin,North China are demonstrating that the atmospheric oxygen concentrations had reached>4%PAL(present atmospheric levels)at least during 1.59-1.56,1.44-1.43,and 1.40-1.36 Ga.These estimated values are higher than the previously recommended values of<0.1-1%PAL.Such a scenario discovered in the Yanliao Basin is consistent with the synchronously deposited strata in Australia and Siberia,pointing to a Mesoproterozoic oxygenation event(1.59-1.36 Ga)between the two major oxygenation intervals during the Proterozoic.This Mesoproterozoic oxygenation event is coupled with the break-up of the Columbia(Nuna)supercontinent,the formation of organic-rich shales and Fe-Mn deposits,and the early innovation of eukaryotic algae,indicating that the geological and biological co-evolutionary processes control the Earth surface system.