A recent study has suggested that microbes residing in the Earth’s crust make up for the majority of microbial life on the planet. Microbes have been known to reside as deep as 3 miles below Earth’s surface, and it is very likely that they can live even beyond. Since not much is known about how the deep biosphere has evolved over time. There isn’t much information available on how modern microbes are related to their ancient predecessors in the subsurface either.

The research paper was written by Peter Reiners, a professor of geosciences and associate dean of the University of Arizona College of Science, and Henrik Drake, an associate professor at the Linnaeus University in Sweden. Published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) this month, the study sheds light on the extent of microbial life present on the earth.

For their research, Reiners and Drake focused on one of common habitats of microbes, Precambrian cratons, known to be the oldest rocks still present today. Through this research, the two scientists went ahead to find out where and when the subsurface microbes should have been active on the planet hundreds of millions to billions of years ago. It should be noted that the Precambrian cratons are natural habitats to microorganisms that receive energy from consumption of nutrients, including meagre organic carbon, and chemical reactions among fluids and rocks.