Precambrian time covers the vast bulk of the ... The earliest living organisms were microscopic bacteria, which show up in the fossil record as early as 3.4 billion years ago.

these ancient rocks contain the tiny fossilized remains of protists and bacteria, and when University of Wisconsin-Madison geologist Stanley Tyler discovered the first microfossils in Precambrian ...

During the Proterozoic era, oxygen produced by photosynthesizing bacteria collects in the oceans ... we know there was plenty of iron in Precambrian waters. Iron normally stays dissolved in ...