Billions of years ago, before Earth's atmosphere had oxygen, it periodically possessed a "haze" of organic chemicals including methane, boffins have discovered. During these periods the planet's air was more like that of Titan, ice moon of Saturn, than the stuff we breathe today. "Models have previously suggested that the Earth's early atmosphere could have been warmed by a layer of organic haze," says Dr Aubrey Zerkle of Newcastle uni. "Our geochemical analyses of marine sediments from this time period provide the first evidence for such an atmosphere." According to Zerkle and his colleagues, during the period 2.5 to 2.65...