Researchers say the Earth had much more oxygennearly a billion years ago than scientific experts thought.That claim could change theories about how life developed on our planet.The claim came from researchers at Brock University in Canada.They wanted to measure the levels of oxygenin the Earth's atmosphere nearly a billion years ago.To do this, the researchers developed a wayto study small air bubbles trapped in ancient salt crystals."There was a lot of debate as to what the oxygen content was800 million or more years ago,"said Nigel Blamey of Brock University's Department of Earth Sciences.He said the trapped gasses showed that the oxygen levelwas about half of what it is today.In fact, many experts believed that the oxygen levelwas only about two percent of the atmosphere so long ago.But the new study found that it was almost 11 percent.Currently, oxygen is about 21 percent of the atmosphere.The Canadian researchers used a methodto study air bubbles trapped in halite, the natural form of table salt.The researchers say their findings have major effectsfor theories about how and when life developed.Professor of Earth Sciences Uwe Brand said that higher oxygen levels in the pastmay turn back the clock when complex life developed."Now paleobiologists will have reason to go looking for rockswith" evidence of these first evolutionary steps,"he told the Canadian Broadcasting Corporation.