Ancient rocks found in Western Australia provide evidence that suggests the presence of high levels of oxygen in Earth's atmosphere approximately two billion years ago. This discovery challenges previous assumptions about the timing of the Great Oxidation Event (GOE), a major shift in Earth's history when atmospheric oxygen levels significantly increased.

The research, led by a team from Curtin University in Perth, Australia, examined iron formations, which are sedimentary rocks formed from iron oxides and other minerals. These rocks are sensitive recorders of ancient environmental conditions, including the levels of oxygen in the atmosphere.

By analyzing the iron formations, the researchers found evidence of significant oxygen production by photosynthetic cyanobacteria, dating back to around 2.2 billion years ago. This indicates that oxygen levels were already substantial at that time, earlier than previously thought.

The study challenges the prevailing view that the GOE occurred around 2.4 billion years ago. Instead, it suggests that the rise of oxygen may have been a gradual process, beginning as early as 2.2 billion years ago and continuing over several hundred million years.

This has important implications for understanding the evolution of life on Earth. The availability of oxygen was crucial for the development of aerobic respiration, which allowed more complex and efficient forms of life to flourish. The earlier presence of oxygen could potentially push back the timeline for the emergence of complex life forms.

The research findings are published in the journal Nature Geoscience.