Until the early 1990s, no one suspected how active the life of the inhabitants of the earth's depths could be. Scientists now believe that microbes living underground may have helped shape continents, release oxygen, and give life as we know it. Atlantik magazine discusses how studying these microorganisms on our planet can help detect life in space, such as Mars.
They live thousands of meters below the surface of the Earth. They feed on hydrogen and emit methane. And they are capable of changing our world more fundamentally than we can imagine.
Alexis Templeton recalls January 12, 2014 as the day the water exploded. A Pyrex glass bottle that was tightly closed and filled with water exploded like a balloon.
Templeton was driving her Land Cruiser over the bumpy and rocky surface of the Wadi Lawayni Valley, which is a wide swath cutting through the mountains of Oman. She parked her car next to a concrete platform overlooking where a water well was recently drilled. Templeton opened the lid of this well and lowered the bottle into its gloomy depths, hoping to get water samples from a depth of about 260 meters.
The Wadi Lavaini Valley is surrounded by rocky peaks of chocolate brown color, these rocks are hard as ceramics, but they are rounded and drooping, more like ancient bricks made of mud. This fragment of the interior of the Earth, the size of the state of West Virginia, was squeezed to the surface by the collision of tectonic plates millions of years ago. These exotic rocks - they represent anomalies on the Earth's surface - made Templeton come to Oman.
Soon after she lifted the water bottle from the depths of the well, she burst open under internal pressure. Water splashed out of the cracks and sizzled like soda. The gas that exploded inside her was not carbon dioxide, as in soft drinks, but hydrogen, a combustible gas.
Templeton is a geobiologist at the University of Colorado in Boulder, and this gas is of particular importance to her. “Organisms love hydrogen,” she says. That is, they love to eat it. By itself, hydrogen cannot be considered evidence of life. However, it suggests that rocks beneath the Earth's surface may be exactly where life can thrive.
Templeton is one of an increasing number of scientists who believe that the depths of the Earth are filled with life. According to some estimates, this unexplored part of the biosphere may contain from one tenth to half of all living matter on Earth.
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Scientists have discovered microbes that inhabit granite rocks at a depth of about two kilometers (6,000 feet) in the Rocky Mountains, as well as in marine sedimentary rocks dating back to the time of dinosaurs. They even found tiny living things - worms that look like shrimp arthropods, baleen rotifers - in the gold mines of South Africa at a depth of 340 meters (11 thousand feet).
We human beings tend to view the world as solid rock covered with a thin layer of life. However, for scientists like Templeton, the planet looks more like a circle of cheese, the dense edges of which are constantly being destroyed by the multiplying microbes that live in its depths. These creatures feed from those sources that not only seem inedible, but also intangible - we are talking about the atomic decay of radioactive elements, about the process that occurs as a result of the pressure of rocks as they sink into the depths of the Earth and their decomposition, and even, perhaps, about earthquakes.
Templeton came to Oman in order to find hidden oases of life. The hydrogen gas sizzle in 2014 was an important piece of evidence that she was on the right track. So Templeton and her colleagues returned to Oman last January to drill a well to a depth of 400 meters (1,300 feet) and try to find the inhabitants of those depths.
One hot winter evening, a piercing noise rang out across the sun-scorched expanses of the Wadi Lavaina Valley. A bulldozer appeared almost in the center of this valley. And in front of him was a drill shaft capable of rotating at a speed of several revolutions per minute.
Half a dozen people in hard hats - mostly Indian workers hired by a local company - operated the rig. Templeton and half a dozen other scientists and graduate students stood several meters away in the shade of a canopy that swayed in the gentle breeze. All of them, bending over the tables, studied the rock samples that the workers brought upstairs approximately every hour.
This rig was in operation all day, and the incoming soil samples changed color as the depth increased. The first few meters of the rock had an orange or yellow tint, indicating that oxygen from the surface had turned the iron contained in the rock into rusty minerals. At a depth of 20 meters, traces of oxygen disappeared, the stones darkened to a greenish-pink color with black veins.
“A beautiful stone,” Templeton said, stroking the surface with her latex-gloved hand. Her goggles were raised up and resting on straight dark blond hair, revealing cheeks that had darkened from years of work on ships, on tropical islands, in the latitudes of the Arctic and elsewhere. “I hope to see more of this kind of material,” she said.
This greenish-black stone provided her with a glimpse of something that is almost impossible to see elsewhere on our planet.
These rock samples, brought to the surface from great depths, turned out to be rich in iron - iron in the form of minerals that, as a rule, do not survive on the Earth's surface. This underground iron is so chemically reactive, it tends to combine with oxygen so much that when it comes into contact with water underground, water molecules break. It pulls oxygen out of the water and leaves hydrogen behind.
Geologists call this process "serpentinization" because of the sinuous traces of black, green and white minerals it leaves behind. Serpentinization usually occurs in places inaccessible to humans, including at a depth of several thousand meters under the floor of the Atlantic Ocean.
And here, in Oman, the rocks located in the depths of the earth come so close to the surface that serpentinization occurs only a few hundred meters underfoot. The hydrogen that tore apart the Tempelton water bottle in 2014 was a small example of the serpentinization process; a water well drilled several years ago in this region produced so much hydrogen that there was even a threat of an explosion, and as a result, the government was forced to urgently concrete it.
Hydrogen is a special substance. It has been used as one of the propellants for launching Apollo spacecraft and shuttles into orbit, and it is one of the most energetically rich elements naturally occurring on Earth. This makes it an important food for the microbes that exist below the Earth's surface.
Fragments of rock intended for geological research.
In total, microbes living under the mountains in eastern Oman can consume tons of hydrogen every year, resulting in a slow and controlled combustion of the gas, precisely controlled by enzymes inside their water-filled cells.
However, hydrogen is only one half of the equation for life - in order to produce energy from hydrogen, microbes need something else to burn it, just as the human race is forced to inhale oxygen to process food. Templeton's main task is precisely to understand what microbes "breathe" with at such a depth under the Earth, where there is no oxygen.
At two o'clock in the afternoon, a battered pickup truck heads to the drilling site along a dusty and muddy road. Behind him are - strictly one after the other - six camels, their heads swaying in the wind. These are local animals, they are tied with short leashes, and they are heading for a new pasture located somewhere in this valley.
Templeton, forgetting about the camels, suddenly cried out, not hiding her excitement: "Gold!" She pointed to a sample of soil on the table, as well as a small cluster of yellow metal crystals. Their cubic shape helped to understand her little joke: these crystals were not real gold, but the gold of fools, which is also called iron pyrite.
Iron pyrite is composed of iron and sulfur, and this is one of the minerals, which is also called "biogenic": its formation is sometimes associated with the activity of microbes. The crystals themselves can be formed from the waste that microbial cells "breathe out". Therefore, pyrite can be a byproduct of microbial metabolism, a possibility Templeton calls "beautiful."
Back home in Colorado, she will give these crystals the same attention that an archaeologist would devote to a pile of ancient Roman rubbish. She will cut them into transparent pieces and examine them under a microscope. If pyrite is actually a product of living cells, then microbes "can probably be buried in minerals." She hopes to find their fossilized bodies.
Until the early 1990s, no one suspected how active the life of the inhabitants of the earth's depths could be. The first evidence was found in the rock beneath the seabed.
Geologists have long noticed that volcanic gases found in dark basaltic rocks are thousands of meters below the seafloor, which often has microscopic depressions and tunnels. “We had no idea that it might be biological,” says Hubert Staudigel, a volcanologist at the Scripps Institute of Oceanography in La Jolla, California.
In 1992, a young scientist named Ingunn Thorseth of the University of Bergen in Norway suggested that these depressions are the geological equivalent of dental caries - microbes embedded it in volcanic glass by consuming iron atoms. In fact, Thorset discovered what could be mistaken for dead cells within these depressions in rock collected three thousand feet below the sea floor.
When these discoveries were published, Templeton was not yet working in the field. She received her master's degree in geochemistry in 1996 and then went to work at the Lawrence Berkeley National Laboratory in California, where she studied how quickly microbes eat aviation fuel in the ground at a former US naval base. A few years later, for her doctoral dissertation at Stanford University, she studied how underground microbes metabolize lead, arsenic and other pollutants during the metabolism.
In 2002, she moved to Scripps Lab to work with Professor of Biology, Bradley Tebo, and Staudigel, on similar issues, namely how microbes live in iron and other metals in the basalt glass found in the seabed.
In November of that year, on the rear deck of a research vessel in the center of the Pacific Ocean, she climbed through a hatch into the car-sized Pisces-IV submersible and plunged into the seabed. Terry Kerby, a pilot at the Hawaii-based Seabed Research Laboratory, pointed the craft towards the southern slope of the Loihi Seamount, an underwater volcano near Hawaii's Big Island.
At 1,700 meters (5,600 feet), the submarine's searchlight barely illuminated the strange underwater landscape - a jumbled mix of what looked like tightly packed garbage bags piled up in a mess in a pyramid of some sort. These so-called basalt cushions formed over the centuries as the lava percolated through cracks collided with sea water, after which it quickly cooled, turning into smooth stones. Templeton lay on her side of the bench, shivering in the cold, watching through the thick glass as Kirby chipped off chunks of basalt with a mechanical arm. Eight hours after the start of the dive to the ocean floor, they returned to the surface with five kilograms of rock.
In the same year, she and Stuadigel visited the Kilauea volcano in Hawaii, hoping to collect microbial-free volcanic glass that they could compare to samples collected from the ocean floor. Wearing heavy boots, they did not come to the lava flow and walked over the petrified crust, which was only a few inches thick. Staudigel found one spot where orange molten lava broke through the resulting solidified crust. He picked up a piece of hot lava with a metal bar - it looked like hot and sticky honey - and placed it in a bucket of water. The water boiled with a whistle and noise, and after a while the lava hardened, turning into glass.
Back in the lab, Templeton isolated dozens of bacterial strains that absorb iron and manganese from rocks at the bottom of the sea. Together with her colleagues, she again melted sterile glass from the Kilauea volcano in a furnace, added various amounts of iron and other nutrients to it, and grew bacterial strains from them. She used the most advanced technology, including X-rays, and watched with delight as bacteria recycle minerals.
“My whole basement was filled with basalt rocks raised from the bottom of the sea, because I simply could not refuse them,” she told me one of those days when there was no drilling.
However, these rock samples, as well as the bacteria that fed on them, had, from Templeton's point of view, one big drawback - they were taken from the seabed, where the water already contains oxygen.
Oxygen is part of all living things on Earth - from aardvarks and earthworms to jellyfish; our atmosphere and most of the oceans are filled with it to redistribution. However, the Earth has had so much oxygen for only a small period of its history. Even today, vast parts of our planet's biosphere have never encountered oxygen. It is enough to plunge into the ground a few meters, and there will no longer be any oxygen. In any other place in the solar system, including Mars, where life can exist, you will not find any oxygen.
While Templeton was studying the deep biosphere of the Earth, she also became interested in the question of the origin of life on our planet and in other places in the solar system. Exploring underground space may provide a glimpse of these separated places and times, but that will only be possible if she can go deeper, beyond the reach of oxygen.
The mountains of Oman seemed to be the ideal location for this kind of exploration. This huge mass of rock, gradually subjected to serpentinization, has oxygen-deprived places inside it, as well as chemically active iron compounds, which, according to scientists, are located in the depths of the Earth.
Templeton and several other deep biosphere researchers were involved with another major project in the early stages of planning, the Oman Drilling Project.
The project is being led by Peter Kelemen, a geologist at the New York-based Lamont-Doherty Earth Observatory. It has its own mission - deep-seated rocks in Oman interact not only with oxygen and water, but also with carbon dioxide, squeezing gas into the atmosphere and enclosing it in carbonate minerals - this process, if scientists can understand it, will help humanity to reduce emission of carbon dioxide into the atmosphere.
Kelemen was present while drilling in Wadi Lavaini in January 2018. He was confident that evidence of life would be discovered. These rocks originally formed at temperatures over 980 degrees Celsius (1800 degrees Fahrenheit). However, they cooled quickly, and today the temperature in the upper layer, which is about 500 meters deep, has a temperature of about 30 degrees Celsius (90 degrees Fahrenheit). These rocks "were not hot enough to kill all microbes since the Cretaceous" - the era of the dinosaurs.
At three o'clock in the afternoon, half a dozen crew members gathered at the oil rig for a kind of ritual that everyone awaits with intense attention.
A new portion of the core, just taken from the drilled shaft, is lowered onto the trestle. We are talking about a stone cylinder three meters high - it roughly corresponds in thickness to the thick end of a baseball bat, and it is located in a metal cylinder.
Workers lifted one end of this pipe. And the core slipped out of it - along with the black and sticky liquid. Black, thick mud spilled onto the ground. The core extracted from the ground was completely covered with this substance.
“Oh my God,” someone said. - Wow . All around were whispering.
One of the workers wiped off the recovered core, after which small bubbles began to form on its smooth and shiny surface, like in boiling oil. This rock sample, unaffected by the pressure it experienced underground, released gases right before our eyes, and its bubbles seeped through the pores in the rock. The smell of sewage and burning rubber began to seep into the air - the smell that the scientists present there immediately identified.
“It's a very lively rock,” Templeton said.
"Hydrogen sulfide," Kelemen said.
Hydrogen sulfide is a gas that forms in the sewers, in your intestines, and also - now obviously - underground in Oman. It is produced by microbes living in the absence of oxygen. Deprived of this life-giving gas, they do a trick that animals living on the planet's surface are not capable of - they begin to breathe something else. In other words, they burn their food using other chemicals found underground.
Part of the core raised to the surface was pierced with stripes of orange-cinnamon stone - this is how the places through which hot lava poured through deep cracks on the earth's surface millions of years ago were marked, and at that moment this rock was in the bowels of the Earth at a depth of several kilometers …
These traces of fossilized magma gradually gave their chemical constituents to groundwater - including molecules called sulfates, which are composed of one sulfur atom bonded to four oxygen atoms. Apparently, microbes used these molecules to digest hydrogen, Templeton said. “They eat hydrogen and breathe out sulfate.” And then they still release their gases.
Hydrogen sulphide not only has a strong and unpleasant odor. It is also toxic. Therefore, the very microbes that produce it are at risk of being poisoned as it accumulates underground. How do they manage to avoid poisoning? Once again, the rock provides us with the answer.
Drilling continued over the next few days, but the black slurry gradually disappeared. Each new core brought to the surface was dry and odorless. However, the rock itself has changed - its vein-like mosaic and serpentine darkened, and its main shades were gray and black, and it began to resemble a plaid skirt dipped in ink.
“All of this blackening is bio-product,” Templeton said one evening as she and her colleague Eric Ellison were in an instrument-laden laboratory trailer packing rock samples to be sent home. Some of the stones were in sealed plexiglass boxes, and Ellison moved them using gloves placed on the boxes on the machines - all this gave the impression that there was something sinister in the collected rock samples. However, this precaution was not intended to protect the person; this was done in order to deprive sensitive microbes of contact with oxygen.
Templeton believed that it was these microbes that had an effect on recent rock samples - the hydrogen sulphide they breathed out reacted with the rock to create iron sulphide, a harmless black mineral. The pyrite we saw earlier is also composed of iron and sulfur, and it could have formed in the same way.
These black minerals are more than just academic rarities. They provide a glimpse into how microbes were not only able to survive in the earth's crust, but were able to alter it, and in some cases even create minerals that do not exist elsewhere.
Some of the richest deposits of iron, lead, zinc, copper, silver, and other metals were formed when hydrogen sulphide collided with those metals deep underground. These sulphides captured these metals and, by concentration, turned them into minerals that formed over millions of years - until they were brought to the surface by miners. The hydrogen sulphide that formed these ores was often of volcanic origin, but in some cases it was formed by microbes.
Robert Hazen, a mineralogist and astrobiologist at the Carnegie Center in Washington, DC, believes that more than half of minerals owe their existence to life forms - plant roots, corals, diatoms, and even underground microbes. He is even ready to suggest that the seven continents of our planet owe their existence in part to microbes that eat away rocks.
Four billion years ago, the Earth did not have a permanent land - only a few volcanic peaks towering over the ocean. However, microbes on the seabed helped change this situation. They attacked basaltic deposits in much the same way they do today, converting volcanic glass into clay minerals. And after softening, they become solid again, turning into new rocks - into a lighter and more malleable material than the rest of the planet: granite.
These light granites coalesced and rose above the surface of the ocean, thus creating permanent continents. Apparently, this process, you to a certain extent, took place without the help of microbes, but Hazen believes that they accelerated it. “You can imagine microbes creating a balance,” he says. "We argue that microbes played a fundamental role."
The emergence of land has a significant impact on the evolution of the Earth. Rocks under the influence of air collapsed faster, releasing nutrients such as molybdenum, iron and phosphorus into the ocean. These nutrients have promoted the growth of photosynthetic algae that absorb carbon dioxide and release oxygen. About two billion years ago, the first traces of oxygen appeared in the earth's atmosphere. 550 million years ago oxygen levels finally reached the levels needed to support primitive animals.
The abundant amount of water on Earth, as well as its optimal removal from the Sun, made it a promising incubator for life. However, its transformation into a paradise for sentient and oxygen-breathing animals was never guaranteed. Microbes may have brought our planet to an invisible turning point - the formation of continents, oxygen and the formation of life as we know it.
And even today, microbes continue to make and remake our planet from the inside.
In some respects, underground microbes resemble human civilization, where “cities” are formed at the crossroads. In Oman, a thriving oasis of odorous black microbes was located at a depth of 30 meters, near the intersection of several large cracks in the rock - these are the channels that allowed hydrogen and sulfates to seep there from various sources.
Elisabetta Mariani, a structural geologist at the University of Liverpool in England, spent many days under a tent, fixing these cracks in the rocks. One morning she called me in to show me something special - a rip that ran diagonally across the core, and there you could see two rock surfaces pierced with layers of green and yellow serpentine as thin as a sheet of paper.
"Do you see these ruts?" she asked in English with an accent that betrayed her native Italian, and pointed to cracks in two serpentine surfaces. They testified that this was not just a passive fracture - it was an active fault. “Two blocks of rock moved, touching each other, in that direction,” she said, pointing to the ruts.
Tullis Onstott, a geologist at Princeton University who is not involved with the drilling project in Oman, believes that such active fractures can not only provide pathways for food to move underground - they may have produced food. In November 2017, Onstott and his colleagues began a daring experiment. They began their work in a tunnel at a depth of 2500 meters in the Moab Khotsong gold mine in South Africa and from there drilled a new well in the direction of a fault that was another 800 meters deeper. On August 5, 2014, an earthquake of magnitude 5.5 occurred in this fault. Onstott hoped in this way to test the provocative idea that earthquakes could provide food for the deep biosphere.
Scientists have long noticed that hydrogen gas is leaking from large faults, including the likes of San Andreas in California. Part of this gas is a chemical reaction - silicate minerals that break down during an earthquake react with water and release hydrogen as a by-product. For microbes near the rift, this kind of reaction can lead to something like a periodic energy explosion associated with a large intake of sugar.
In March 2018, four months after drilling began at the Moab-Hotsong mine, workers brought a core to the surface that crossed the fault.
The rock along the fault was “pretty badly destroyed,” Onstott says - a dozen parallel fractures could be seen on the core. The surface of some of these cracks turned into brittle clay, streaks of which indicated recent earthquakes. Other cracks were filled with veins of white quartzite, which denoted older fractures that had formed thousands of years earlier.
Onstott is currently searching for fossilized cells in these quartzite veins, and is also analyzing the rock for DNA, hoping in this way to determine which bacteria live in this rift, if any.
In addition, he and his colleagues - and more importantly - have left the drilled holes open and are monitoring water, glass and microbes in the fault itself, and taking new samples every time there is a second earthquake. "In this case, you can see if glass is released or not," he says, "and also observe whether any changes in the microbiological community are taking place as a result of gas consumption."
While Onstott awaits these results, he is also speculating on a more radical possibility: These deep-seated bacteria not only feed on the effects of earthquakes, but they may cause them. In his opinion, when microbes begin to attack iron, manganese and other elements in minerals that appear along the fracture lines, they can weaken the rock - and prepare those fractures for the next big strike. Investigating this possibility involves conducting laboratory experiments to determine if bacteria in these fractures are actually capable of breaking down minerals quickly enough to affect seismic activity. With a characteristic underestimation of the significance of the scientist, he thinks about the forthcoming work: "This is a reasonable enough hypothesis to test it."
On January 30, the drilling rig in Wadi Lavaini reached 60 meters. Her motors roared in the background sound as Templeton and her colleague Eric Boyd sat in field chairs under an acacia tree. Alongside them were signs of other travelers vacationing in this island of shadow, rare in the area - camel droppings, smooth and round like leathery plums.
“We believe the environment is essential to understanding the origins of life,” said Boyd, a geobiologist at Montana State University in Bozeman. In his opinion, this is what makes him and Templeton study the deep rocks in Oman. “We love hydrogen,” he says.
Both Boyd and Templeton believe that life on Earth originated in an environment similar to the one that exists several meters below their field folding chairs. According to them, the cradle of life lies in the rifts below the Earth's surface, where iron-rich minerals squeezed hydrogen out of themselves after contact with water.
Of all the chemical fuels that existed on Earth four billion years ago, hydrogen appears to be one of the easiest elements for the metabolism of early and inefficient cells. Hydrogen was not only produced by serpentinization, it was also produced - as it does today - from the radioactive decay of elements such as uranium, which continually breaks down water molecules in the surrounding rock. Hydrogen is so unstable, it tends to decompose so much that it can be digested even by mild oxidants like carbon dioxide or pure sulfur. A study of the DNA of millions of gene sequences suggests that the forerunner of life on Earth - the "last universal common ancestor" - may have used hydrogen as food and burned it with carbon dioxide. Same,it is probably possible to say about life in other worlds.
Iron-containing minerals here in Oman are often found in the solar system, as is the process of serpentinization. The Orbiter space probe, which is currently orbiting Mars, has discovered serpentine minerals on the surface of Mars. The Cassini spacecraft has found chemical evidence of ongoing serpentinization deep in Enceladus, the ice-covered moon of Saturn. Minerals similar to serpentine have also been found on the surface of Ceres, a dwarf planet whose orbit lies between the orbits of Mars and Jupiter. Serpentines have even been found in meteorites, in fragments of embryonic planets that existed 4.5 billion years ago, that is, just at the time of the birth of the Earth, and this may mean that the cradle of life, in fact, existed before the formation of our planet.
Hydrogen - the source of energy for nascent life - has been found in all these places. It may still be produced throughout the solar system.
Boyd’s conclusions are breathtaking.
“If you have this kind of rock, and the temperature is comparable to that on Earth, and if you still have liquid water, how inevitable do you think life is?” He asks. "Personally, I'm sure it's inevitable."
Finding life will be a challenge. With existing technology, a spacecraft sent to Mars can drill a hole just a few feet deep into hostile surfaces. These surface rocks may contain traces of a past life - perhaps the dried-up foundations of Martian cells in the microscopic tunnels they gnawed through the minerals - but any living microbes are likely to be several hundred feet deep. Templeton is trying to find traces of a past life - and also to separate those signs from those things that have not been affected by life - and she has done so since the moment she examined basalt glass at the bottom of the sea 16 years ago.
“My job is to find biological prints,” she says. She uses the same tools to study samples brought from Oman as she does to study glass. She shoots the surfaces of minerals with X-rays in order to understand how microbes modify minerals. She also wants to understand: do they leave them in place? Or do they corrode them? By studying which living microbes absorb minerals, she hopes to find a reliable way to identify the same chemical traces of absorption in extraterrestrial rocks that have not had any living cells for thousands of years.
One day these kinds of instruments will be aboard a rover. Or they will be used in the study of rock samples brought from other worlds. In the meantime, Templeton and her colleagues still have a lot of work to do in Oman - they will need to figure out what contains the dark, hot and hidden biosphere beneath their feet.
Douglas Fox