New research suggests oxygen was being produced on Earth hundreds of millions of years before any traces of it appeared in our atmosphere, U.S. scientists say. Studies at Massachusetts Institute of Technology indicate that early oxygen kept a low profile in \"oxygen oases\" in the oceans where tiny aerobic organisms may have evolved to survive on extremely low levels of the gas in these undersea pockets. It wasn\'t until the \"Great Oxidation Event\" nearly 2.3 billion years ago that oxygen appeared in any measurable quantity in the atmosphere, stimulating the evolution of air-breathing organisms and, ultimately, the complex life of the Earth today, an MIT release said Tuesday. \"The time at which oxygen became an integral factor in cellular metabolism was a pivotal point in Earth history,\" MIT geobiology professor Roger Summons says. \"The fact that you could have oxygen-dependent biosynthesis very early on in the Earth\'s history has significant implications.\" The research suggests oxygen may have been present on Earth 300 million years before it appeared in the atmosphere, just at extremely low concentrations that wouldn\'t have left much of a trace in the rock or fossil record.