Underfoot, miles deep, there are enormous ecosystems rich in Amazons and larger than all the oceans of the planet.
But this world barely explored and watched you need strong microscopes.
"It's as if we've found a whole new reservoir of life on our planet," he said. Karen Lloyd, a researcher at the University of Tennessee in the United States.
Lloyd is one of the scientists involved in the project Deep Observatory, Deep Observatoryor DCO,
More than 1,200 scientists from 52 countries have contributed to this ambitious project that studies life under the Earth's surface. And the first results were presented this week at the US Geophysical Meeting in Washington DC.
"Almost 70% of all microbes on Earth are under our feet"Lloyd said.
"It will change our perception of where life is on Earth, and we enjoy it from the surface where trees, whales, or dolphins are in the underground world where most of life is on the planet."
At a depth of more than 5 km
Despite extreme heat, lack of light, rare nutrients, and tremendous pressure flourish the beings of this underground world.
Scientists have estimated that underground organisms represent 15,000 to 23,000 million tons of carbon, a hundred times more than the content in all human beings.
Scientists came to this estimate pierced the earth's surface and took it samples with a depth of more than 5 km, both underground and under sea.
From these samples, the researchers quantified the living cells of the organisms in the specified volumes.
Based on these records, they used models to estimate the total number of biomass underground.
"Although these samples are just points on a vast planet, we have studied ecosystems so different that we can arrive at a reasonable estimate of the carbon contained in these forms of life," he said. Rock Colwell, an expert on microbial ecosystems at the University of Oregon.
Microbes and minerals
Scientists estimate that the deep biosphere is between 2,000 and 2,300 million cubic kilometers, almost twice the volume of all oceans,
The most common underground organisms are prokaryotes, ie microbes without nucleus contained in the membrane, including bacteria and the so-called Archaea, unicellular organisms with an evolutionary history distinct from bacteria.
Scientists, however, also found eukaryotic organisms, ie microorganisms or multicellular organisms with cells that contain the nucleus in the shell.
Microbes of this deep world can not use solar radiation to get energy, so they do not use photosynthesis chemosynthesis feeding
In other words, they acquire chemical energy and nutrients from the minerals surrounding them.
"They can live thousands of years"
One of the organisms found lives at 2.5 km deep and is a methanogen that produces methane that is not used for reproduction but for repair itself.
Underground lives also live in completely different time ranges.
"It's the strangest thing for me some from them organisms can live for thousands of years"They're metabolically active, but they use less energy than we thought was necessary for life," Lloyd explained.
Some of the microorganisms that live for thousands of years only move when tectonic plates, earthquakes or eruptions occur.
"We humans have relatively fast processes, sun-day cycles or moon-based moon cycles, but these organisms are part of very slow cycles on geological scales," Colwell said.
The discovery was made possible by new drills that drill deeply and more powerful microscopes that capture increasingly small forms of life.
The study allows scientists to better understand one of the basic processes that govern life on Earth: the carbon cycle.
"You can not understand the role of carbon on our planet without understanding its diversity," said the executive director of the project, Bob Hazen,
"Cells process carbon, absorb and exhale, make incredible things to change the environment in which they live."
Details of this underground world also have consequences for finding life on other planets.
"There is currently a known temperature limit for life to be there 122 degrees Celsius, where the equipment in the laboratories is sterilized, "Lloyd said.
"But I do not know any scientist who thinks it's an absolute theoretical limit," a researcher at the University of Tennesee said.
"For example, we know that if the temperature is very high, it will affect the integrity of the membranes and lipids."
"But if the pressure is higher, the temperature limit will change, and that means organisms could be at higher temperatures how the depth increases. "
For Colwell, "we have seen on Earth that organisms can survive far away from sunlight using the energy of deep rocks."
And that means "it is likely to assume that the subsoil of other planets and moons can be habitable."