Preston Cloud

Preston Ercelle Cloud Jr. was an American geologist and paleontologist, born in 1912 and died in 1991, whose research focused on the Precambrian biosphere and the history of atmospheric oxygen. In a landmark 1968 paper he argued that Earth's ancient banded iron formations could only have formed in oceans lacking free oxygen, and that rising atmospheric oxygen roughly two billion years ago explained why such iron formations stopped forming afterward, tying the geological record directly to the evolution of early life. He worked for years as a preparator and researcher in Paleozoic fossil brachiopods at the United States National Museum before turning to Precambrian biogeology.