Stromatolites — mats of bacteria that trap and precipitate sediments — were rare in the early Precambrian era, but they became more common 2.6 billion years ago, when shallow seas were more extensive. Because the atmosphere during much of the Precambrian had little oxygen, there was no protective ozone layer, and life could prosper only in water of just the right depth — shallow enough for sunlight to penetrate, but deep enough to block out the Sun’s harmful ultraviolet radiation.
Topic: Earth Science
Subtopic: Earth Structure
Keywords: Geology, Stratigraphic--Precambrian, Life--Origin, Paleoclimatology, Stromatolites
An entire colony of microbes piled on one another over time, forming semi-rigid, upward-pointing, and branching columns mirrored in this 900-million-year-old stromatolite.