Scientists Push Back Origins Of Earth's Oxygen

Scientists examining rocks dating back 2.5 billion years said on Thursday they found evidence shedding light on one of the landmark events in Earth's natural history -- the appearance of life-nurturing oxygen as a major part of the atmosphere. Recovered from deep underground, this shale dating from about 2.5 billion years ago contained material untouched by the atmosphere for billions of years. Sedimentary rocks can harbor evidence of oxidation and other chemical reactions that occur as the rocks form. This oxygen, the scientists believe, was produced via photosynthesis by some of the simple organisms that inhabited the planet at the time, a type of aquatic bacteria sometimes called blue-green algae. Oxygen is vital for most life forms on Earth...