The Phantom Biosphere -- "An Alien Life-Form May Exist Hidden in Earth's Microbial World"
The history of life on Earth is largely microbial. "You can certainly run a world without dinosaurs and humans, but you can’t do it without microbes.’ says Harvard Fisher Professor of Natural History and Professor of Earth and Planetary Sciences, Andrew H. Knoll. "For vast stretches of time, bacteria and other single-celled organisms were the only life on Earth. The age of the dinosaurs to the present day," Knoll said, "represents roughly 5 percent of the history of life."