Preston Cloud

In academia, he was a member of the faculty of Harvard University, University of Minnesota, University of California, Los Angeles, and lastly University of California, Santa Barbara. He was best known for his work on the geologic time scale and the origin of life on Earth, and as a pioneering ecologist and environmentalist. His works on the significance of Cambrian fossils in the 1940s led to the development of the concept "Cambrian explosion," for which he coined the phrase "eruptive evolution." His work from the 1960's through the 1970's on the significance of certain mineralogical differences between sedimentary rocks laid down before and after about 2.5Ga (2.5 billion years ago), as well as the timing of the worldwide deposits of Banded Iron Formations (BIF) compared with that of continental red beds, led him to propose the now well-accepted concept of a turning point in Earth's history (now known as the Great Oxidation Event or GOE) in the beginning of the Proterozoic eon, during which Earth's oceans and atmosphere first became enriched in O2 (molecular oxygen), allowing the later emergence and radiation of complex multicellular life.