Earth Had Oxygen Much Earlier Than Thought

[muriel_volestrangler]

2. It indicates some oxygen, but not necessarily anything approaching present-day amounts

Here's the abstract of the letter to Nature:

It is widely assumed that atmospheric oxygen concentrations remained persistently low (less than 10−5 times present levels) for about the first 2 billion years of Earth’s history1. The first long-term oxygenation of the atmosphere is thought to have taken place around 2.3 billion years ago, during the Great Oxidation Event2, 3. Geochemical indications of transient atmospheric oxygenation, however, date back to 2.6–2.7 billion years ago4, 5, 6. Here we examine the distribution of chromium isotopes and redox-sensitive metals in the approximately 3-billion-year-old Nsuze palaeosol and in the near-contemporaneous Ijzermyn iron formation from the Pongola Supergroup, South Africa. We find extensive mobilization of redox-sensitive elements through oxidative weathering. Furthermore, using our data we compute a best minimum estimate for atmospheric oxygen concentrations at that time of 3 × 10−4 times present levels. Overall, our findings suggest that there were appreciable levels of atmospheric oxygen about 3 billion years ago, more than 600 million years before the Great Oxidation Event and some 300–400 million years earlier than previous indications for Earth surface oxygenation.

http://www.nature.com/nature/journal/v501/n7468/full/nature12426.html

A minimum of 3x10-4 times present levels.