How Earth's atmosphere transformed from oxygen-poor to oxygen-rich over a span of about two billion years has been revealed by an international team of researchers.
Dr Matthew Dodd, from The University of Western Australia's School of Earth Sciences, collaborated on the study, led by Chengdu University of Technology and published in Nature.
"Scientists suspected oxygen levels increased on Earth in stages but the precise timing and connections with ocean chemistry and biological evolution are contentious," Dr Dodd said.
"The rise of oxygen in Earth's atmosphere is fundamental to the emergence of oxygen-breathing complex life, planetary habitability and the creation of vital natural resources."
Researchers analysed high-resolution oxygen isotope records preserved in ancient sulphate minerals to reconstruct the rise of atmospheric oxygen and its dynamic interplay with the oceans.
"By systematically sampling the oxygen isotope record across billions of years and integrating previously published data, we built the most complete oxygen isotope-based reconstruction of oxygen evolution spanning the past three billion years," Dr Dodd said.
The results revealed three major episodes of atmospheric oxygen increase – during the Paleoproterozoic (2,500 to 1,600 million years ago), Neoproterozoic (1 billion to 538.8 million years ago), and Paleozoic (538.8 million years ago to 252 years ago) eras – culminating in stable, modern-like levels about 410 million years ago.
Importantly, following the Neoproterozoic oxygen rise, Earth's oceans, which were largely lacking in oxygen, but underwent periodic oxidation pulses.
The events resulted in synchronised carbon, sulphur and oxygen isotope shifts over hundreds of millions of years, which suggests that increasing atmospheric oxygen repeatedly triggered transient ocean oxidation.
"The findings provide an environmental framework for understanding the origin and evolution of life on Earth, as well as the formation of mineral deposits and petroleum resources," Dr Dodd said.
