Researchers give a survey of a decade discovering a vast and mysterious world of deep underground microbes that could explain how life begins on Earth and how it can look on other planets.
"The branches of life we knew were not all there," says Karen Lloyd of Tennessee University. "In fact, there are deep branches of the tree of life that no one ever knew before, and many of them are in the underground."
Lloyd is one of the hundreds of scientists from around the world participating in Observatory Deep Carbon, which explores the effects of carbon many kilometers underground. Team members looking at how this carbon can provide groundwater will present their results this week at the annual meeting of the American Geophysical Union.
Scientists know microbes can live far below the surface since they were first discovered in oil fields in the 20s of the 20th century. But over the last 10 years, it has become clear that the genetic diversity of small creatures living in microscopic pores and veins of rocks under our feet is at least equal to that above the surface.
Almost three-quarters of terrestrial bacteria and archea (a type of microbe) live in the underground, scientists now say. There are all types of cellular life, including the species that make up the known flora and fauna on the surface.
These beasts colonize up to 2.3 billion cubic kilometers – almost twice as many as the oceans. Some live in temperatures up to 121 ° C; others find the existence of more than 10 kilometers under the seas.
Generally, the amount of carbon that contains the bacteria is between 245 to 385 times greater than that found in humans.
This is a strange world where microbes draw energy from sources like radiation, "eat" sulfur and "breathe" the rust.
"So life can be maintained even if it does not have the potential to gain the energy of the sun," said Barbara Sherwood Lolar of the University of Toronto. She found microbes in 2.7 billion years of water deep in the Canadian Shield.
"They breathe other things," said Rick Colwell of the Oregon State University. "Many of them are able to use oxidized iron in the way we use oxygen."
Sherwood Lollar calls it haemosynthetic life, unlike the surface life that depends on photosynthesis.
Things happen slowly down there. Microbes from the depths can reach hundreds or even thousands of years without creating any new cages. Instead, they repair damaged molecules and wait for the next earthquake to open a new nutrient channel.
"These things are happening for a much longer period of time than we are used to waiting for," Lloyd said.
Many questions remain. Among the most intriguing have been whether life has been cut off from the surface or has grown underneath.
"Given that all energy and carbon sources are needed to make life in the deep underworld, and so much of our history has involved a very insatiable superficial world, it is reasonable to assume that life has arisen in the underworld and is climb up, "Lloyd said.
The same logic applies to other planets, Sherwood Lollar said.
"If we go to other planets, photosynthetic life may never have occurred, but maybe haemosynthetic life is," she said.
"This is part of the reason why the study of these deep chemosynthetic organisms on this planet is so directly related to the search for life on other planets."
This is a rare scientist who can help to reveal a whole new perspective on life, Lloyd said.
"We think we have a handle … in general, then everything is thrown out of the window." Every move that we make, we find that nature has so many surprises for us.
– Follow Bob Weber on Twitter on @ row1960
Bob Weber, Canadian Seal