Twenty billion tonnes of bacteria

Scientists have estimated the total amount of life on Earth that exists below ground - and it is vast. You would need a microscope to see this subterranean biosphere, however. It is made up mostly of microbes, such as bacteria and their evolutionary cousins, the archaea. Nonetheless, it represents a lot of carbon - about 15 to 23 billion tonnes of it. That is hundreds of times more carbon than is woven into all the humans on the planet.

"Something like 70% of the total number of microbes on Earth are below our feet," said Karen Lloyd from the University of Tennessee at Knoxville, US. "So, this changes our perception of where we find life on Earth, from mostly on the surface in things like trees and whales and dolphins, to most of it actually being underground," she told BBC News.

The role all these organisms play in shifting carbon about the Earth is profound, according to the DCO's executive director, Bob Hazen. "You cannot understand carbon on Earth without understanding the diversity and influence of life. Cells turn over carbon - they take carbon in, they breathe it out. They do amazing things to transform their local environments," he explained. "Although the total amount of carbon in other sources is much, much larger than in life, life has a disproportionate affect on Earth's carbon cycle."

"The current known upper-limit for life is 122 degrees Celsius, which happens to be the temperature of sterilisation equipment we typically use in labs," said Dr Lloyd. "But there's no-one I know who thinks that's the theoretical limit. For example, we know some of the problems associated with high temperatures, such as the disordering of lipids and membranes, is at least partially compensated by higher pressures. Which means it's possible we could find even higher temperature organisms the deeper we go down."
https://www.bbc.com/news/science-environment-46502570