Early life may have breathed oxygen earlier than believed

Early life may have breathed oxygen earlier than believed A new study suggests that aerobic respiration began hundreds of millions of years before oxygen became abundant in Earth’s atmosphere. Around 2.3 billion years ago, a pivotal period known as the Great Oxidation Event set the evolutionary course for oxygen-breathing life on Earth. But MIT geobiologists and colleagues have found evidence that some early forms of life evolved the ability to use oxygen hundreds of millions of years before that. By mapping enzyme sequences from several thousand modern organisms onto an evolutionary tree of life, the researchers traced the origins of an enzyme that enables organisms to use oxygen to the Mesoarchean period, 3.2 to 2.8 billion years ago. The team’s results may help explain a longstanding puzzle in Earth’s history: Given that the first oxygen-producing microbes likely emerged before the…