Microbes may have lived in the underground for more than a billion years

A study using the thermal history and biosignatures of the upper few kilometers of some of the oldest rocks on Earth place constraints on the evolutionary history of microbes in the deep biosphere. A new study, published in PNAS, Proceedings of the National Academy of Sciences, show that the rocks were uninhabitable for much of their lifetimes with the longest period of habitability not extending much past 1 billion years, and usually much shorter. Understanding the history of the deep biosphere can provide insight into the evolution of life on Earth.