New find pushes earth's oxygenation by 300mn yrs
American researchers have unearthed microscopic air bubbles trapped in rock salt, which they claim predates Earth's oxygenation by 300 million years. At that time, the average oxygen content was found to be 10.9%, half of today's concentration. Till now, two major oxygenation events have reportedly occurred in the earth's 4.5-billion-year history, the first being around 2.4 billion years ago​.