Did Meteorite Impacts Help Create Life on Earth?
Aerial view of Barringer Crater (also known as Meteor Crater) -- a meteorite crater located east of Flagstaff, Arizona and west of Winslow, Arizona. Barringer was the first crater proven to be the result of an impact, and remains one of the world's most well preserved impact sites. The crater stretches 1200 meters across and 170 meters deep, with the rim of the crater rising 45 meters above the surrounding landscape. The area around the impact site is tinted red with oxidized iron from the nickel-iron meteor which impacted there almost 50,000 years ago. The Barringer meteor was very small compared to the object that created the Chicxulub Crater in the Yucatán 65 million years ago. That is the one that is theorized to have led to the mass extinctions of the dinosaurs and is estimated to have been between 6 to 15 kilometers in diameter. Geologist Daniel Barringer, who first suggested that the crater was the result of an impact, was also a wealthy investor in mining operations. Not realizing that the energy released by the impact destroyed most of the meteor, Barringer spent 25 years and hundreds of thousands of dollars mining the center of the crater in search of what he believed was an iron meteor worth millions of dollars. Barringer died of a heart attack in 1929, shortly after reading conclusive evidence that there was no meteor to be found and realizing that he had bankrupted himself searching for it. (Image Credit: NASA, M. Wadhwa, University of Iowa)
Did Meteorite Impacts Help Create Life on Earth and Beyond?
It's among the most fundamental of questions: What are the origins of life on Earth?
What if impact craters, long seen as harbingers of death, turned out to be the cradle of life?
For planetary scientist Gordon Osinski, Director of the Institute for Earth and Space Exploration at Western University in Canada, this isn’t just the big question posed in his latest study, but an overriding theme of his celebrated academic career, according to an article by Jeff Renaud.
The new study, published in Astrobiology, posits that impact craters should be considered by space agencies like NASA and ESA as top exploration targets, not just for their invaluable post-impact geological records, but also – and perhaps more importantly – as prime locations for seeking potential habitats for extraterrestrial life.
“There are a lot of hypotheses for where life started on Earth and where we should look for life on Mars, but we are actually overlooking a major geological force and a key habitat in understanding the origin of life and that’s meteorite impacts and their resulting craters,” said Osinski.
Leading an international team with investigators from the University of Edinburgh, Georgetown University, and the University of Southern California, this new study is grounded in Osinski’s extensive field work and laboratory studies of meteorite impacts over the past two decades.
“If you ask anyone to imagine what happens when you have kilometer-size chunks of rock hitting the Earth, it’s typically destructive. It’s an extinction event like the one that killed the dinosaurs,” said Osinski. “What we’re trying to do here is turn that idea up on its head and say yes, the impact is initially destructive, but it also delivers the building blocks for life and creates new habitats for life. They [the impact craters] essentially create an oasis for life.”
Osinski and collaborators propose that given the pervasive nature of impact events and their increased frequency during the first 500 million years of Solar System history that meteorite impact craters may represent the most likely sites where life originated on Earth. Unfortunately, says Osinski, we’ll never really know.
“Unfortunately, due to billions of years of erosion, plate tectonics, and volcanism, we’ve lost the vast majority of the ancient rock record on Earth. So we’re never going to know exactly where or even when, to be honest, life originated on Earth,” said Osinski.
But maybe it’s not too late for the Red Planet.
By exploring Mars with rovers like Perseverance and ExoMars, Osinski believes planetary scientists might eventually figure out the origin of life – and they just might – as long as they are looking in the right place.
“There are other impact craters on Mars that may have been better to explore with these ideas in mind,” said Osinski. “But Perseverance is going to land in Jezero Crater and there is evidence of minerals such as clays formed through hydrothermal activity. It’s a good place to start to explore the role of meteorite impacts in the origin of life, as long as they look out for the habitats, nutrients, and building blocks for life that we outlined in our study.”
To date, 200 impact craters have been investigated and confirmed on Earth using fieldwork, geophysics, satellite data, and various laboratory analysis techniques in pioneering laboratories at Western and others around the world.
Osinski and his team have collected and posted relevant data for all 200 craters as part of Western’s Impact Earth initiative.
Could Comets Have Seeded Life on Earth?
Three icy comets orbiting among the rocky asteroids in the main asteroid belt between Mars and Jupiter may hold clues to the origin of Earth's oceans.
The comets, discovered in 2006 and dubbed "main-belt comets" by University of Hawaii graduate student Henry Hsieh and Professor David Jewitt, have asteroid-like orbits and, unlike other comets, appears to have formed in the warm inner solar system inside the orbit of Jupiter rather than in the cold outer solar system beyond Neptune.
The existence of these main-belt comets suggests that asteroids and comets are much more closely related than previously thought and supports the idea that icy objects from the main asteroid belt could be a major source of Earth's present-day water.
The crucial observations were made using the 8-meter Gemini North Telescope on Mauna Kea. Hsieh and Jewitt found that an object designated as Asteroid 118401 was ejecting dust like a comet. Together with a mysterious comet (designated 133P/Elst-Pizarro) known for almost a decade but still poorly understood, and another comet (designated P/2005 U1) discovered by the Spacewatch project in Arizona just a month earlier, "Asteroid" 118401 forms an entirely new class of comets.
"The main-belt comets are unique in that they have flat, circular, asteroid-like orbits, and not the elongated, often tilted orbits characteristic of all other comets," said Hsieh. "At the same time, their cometary appearance makes them unlike all other previously observed asteroids. They do not fit neatly in either category."
In both 1996 and 2002, the "original" main-belt comet, 133P/Elst-Pizarro (named after its two discoverers), was seen to exhibit a long dust tail typical of icy comets, despite having the flat, circular orbit typical of presumably dry, rocky asteroids. As the only main-belt object ever observed to take on a cometary appearance, however, 133P/Elst-Pizarro's true nature remained controversial -- Until the discovery of these three new comets.
"The discovery of the other main-belt comets shows that 133P/Elst-Pizarro is not alone in the asteroid belt," Jewitt said. "Therefore, it is probably an ordinary (although icy) asteroid, and not a comet from the outer solar system that has somehow had its comet-like orbit transformed into an asteroid-like one. This means that other asteroids could have ice as well."
The Earth is believed to have formed hot and dry, meaning that its current water content must have been delivered after the planet cooled. Possible candidates for supplying this water are colliding comets and asteroids. Because of their large ice content, comets were leading candidates for many years, but recent analysis of comet water has shown that comet water is significantly different from typical ocean water on Earth.
Asteroidal ice may give a better match to Earth's water, but until now, any ice that the asteroids may have once contained was thought to either be long gone or so deeply buried inside large asteroids as to be inaccessible for further analysis. The discovery of main-belt comets means that this ice is not gone and is still accessible right on the surfaces of at least some objects in the main belt, and at times, even venting into space. Spacecraft missions to the main-belt comets could provide new, more detailed information on their ice content and in turn give us new insight into the origin of the water, and ultimately life, on Earth.
As conventionally defined, comets and asteroids are very different. Both are objects a few to a few hundred miles across that orbit throughout our solar system. Comets, however, are thought to originate in the cold outer solar system and consequently contain much more ice than the asteroids, most of which are thought to have formed much closer to the Sun in the asteroid belt between Mars and Jupiter.
Comets also have large, elongated orbits and thus experience wide temperature variations. When a comet approaches the Sun, its ice heats up and sublimates (changes directly from ice to gas), venting gas and dust into space, giving rise to a tail and a distinctive fuzzy appearance. Far from the Sun, sublimation stops, and any remaining ice stays frozen until the comet's next pass close to the Sun. In contrast, objects in the asteroid belt have essentially circular orbits and are expected to be mostly baked dry of ice by their confinement to the inner solar system. Essentially, they should be just rocks. With the discovery of the main-belt comets, we now know this is not the case, and that, in general, the conventional definitions of comets and asteroids are in need of refinement.
An experiment in 2013 at the University of California - Berkeley and the University of Hawaii - Manoa simulating conditions in deep space reveals that the complex building blocks of life could have been created on icy interplanetary dust and then carried to Earth, jump-starting life.
Chemists from the two universities showed that conditions in space are capable of creating complex dipeptides â€“ linked pairs of amino acids â€“ that are essential building blocks shared by all living things. The discovery opens the door to the possibility that these molecules were brought to Earth aboard a comet or possibly meteorites, catalyzing the formation of proteins (polypeptides), enzymes and even more complex molecules, such as sugars, that are necessary for life.
"It is fascinating to consider that the most basic biochemical building blocks that led to life on Earth may well have had an extraterrestrial origin," said UC Berkeley chemist Richard Mathies.
While scientists have discovered basic organic molecules, such as amino acids, in numerous meteorites that have fallen to Earth, they have been unable to find the more complex molecular structures that are prerequisites for our planet's biology. As a result, scientists have always assumed that the really complicated chemistry of life must have originated in Earth's early oceans.
In an ultra-high vacuum chamber chilled to 10 degrees above absolute zero (10 Kelvin), Seol Kim and Ralf Kaiser of the Hawaiian team simulated an icy snowball in space including carbon dioxide, ammonia, and various hydrocarbons such as methane, ethane, and propane. When zapped with high-energy electrons to simulate the cosmic rays in space, the chemicals reacted to form complex, organic compounds, specifically dipeptides, essential to life.
At UC Berkeley, Mathies and Amanda Stockton then analyzed the organic residues through the Mars Organic Analyzer, an instrument that Mathies designed for ultrasensitive detection and identification of small organic molecules in the solar system. The analysis revealed the presence of complex molecules (nine different amino acids and at least two dipeptides) capable of catalyzing biological evolution on earth.
Did NASA Discover Fossilized Alien Cyanobacteria in a Meteorite?
In 2011, a NASA scientist claimed to have discovered the fossilized remains of an alien life form -- a cyanobacteria in meteorites which have been collected on Earth. According to Dr. Richard Hoover, an astrobiologist with NASA's Marshall Space Flight Center, the alien life form could explain how life on Earth started. Dr. Hoover fractured small meteorite specimens under a sterile environment and then examined the freshly broken surfaces with a scanning-electron microscope and a field emission electron-scanning microscope, which allowed him to search the surface for evidence of fossilized remains.
Dr. Hoover explains that travelling to Antarctica, Siberia, and Alaska, he has studied an extremely rare form of meteorites -- CI1 carbonaceous chondrites -- of which only nine are known to exist on Earth.
"I interpret it as indicating that life is more broadly distributed than restricted strictly to the planet Earth. This field of study has just barely been touched -- because quite frankly, a great many scientists would say that this is impossible."
"The exciting thing is that they [the bacteria] are in many cases recognizable and can be associated very closely with the generic species here on Earth. There are some that are just very strange and don't look like anything that I've been able to identify, and I've shown them to many other experts that have also come up stumped," said Dr. Hoover.
"We have known for a long time that there were very interesting biomarkers in carbonaceous meteorites and the detection of structures that are very similar... to known terrestrial cyanobacteria is interesting in that it indicates that life is not restricted to the planet Earth," Hoover said.
Dr. David Marais, an astrobiologist with NASA's AMES Research Center, is very cautious about jumping to conclusions. "It's an extraordinary claim, and thus I'll need extraordinary evidence," Marais said.
Dr. Rudy Schild, of the Harvard-Smithsonian's Center for Astrophysics and the editor-in-chief of the Journal of Cosmology, where Dr. Hoover's paper has been published said "Dr. Richard Hoover is a highly respected scientist and astrobiologist with a prestigious record of accomplishment at NASA. Given the controversial nature of his discovery, we have invited 100 experts and have issued a general invitation to over 5,000 scientists from the scientific community to review the paper and to offer their critical analysis. No other paper in the history of science has undergone such a thorough vetting, and never before in the history of science has the scientific community been given the opportunity to critically analyze an important research paper before it is published, he wrote."
Dr. Seth Shostak of the SETI Institute said "Maybe life was seeded on earth -- it developed on comets for example, and just landed here when these things were hitting the very early Earth. It would suggest, well, life didn't really begin on the Earth, it began as the solar system was forming."
Dr. Shostak continued "A lot of times it takes a long time before scientists start changing their mind as to what is valid and what is not. I'm sure there will be many many scientists that will be very skeptical and that's OK."
Did Strange Bacterial Life Forms Emerge 800 Million Years After Earth's Formation?
Back in 2017, remains of microorganisms at least 3.77 billion years old were discovered by an international team led by University College London (UCL) scientists, providing direct evidence of one of the oldest life forms on Earth.
Tiny filaments and tubes formed by bacteria that lived on iron were found encased in quartz layers in the Nuvvuagittuq Supracrustal Belt (NSB) in Quebec, Canada.
The NSB contains some of the oldest sedimentary rocks known on Earth which likely formed part of an iron-rich deep sea hydro-thermal vent system that provided a habitat for Earth's first life forms between 3,770 and 4,300 million years ago. Earth was formed 4,543 million years ago, so it appears that life on Earth emerged rather early in its history.
"Our discovery supports the idea that life emerged from hot seafloor vents shortly after planet Earth formed. This speedy appearance of life on Earth fits with other evidence of recently discovered 3,700 million year old sedimentary mounds that were shaped by microorganisms," explained PhD student Matthew Dodd of the UCL Earth Sciences and the London Center for Nanotechnology.
Funded by UCL, NASA, Carnegie of Canada, and the UK Engineering and Physical Sciences Research Council, the study describes the discovery and the detailed analysis of the remains undertaken by the team from UCL, the Geological Survey of Norway, US Geological Survey, the University of Western Australia, the University of Ottawa, and the University of Leeds.
Prior to this discovery, the oldest micro-fossils reported were found in Western Australia and dated at 3,460 million years old but some scientists think they might be non-biological artifacts in the rocks. It was therefore a priority for the UCL-led team to determine whether the remains from Canada had biological origins.
The researchers systematically looked at the ways the tubes and filaments, made of haematite, a form of iron oxide (aka rust), could have been made through non-biological methods such as temperature and pressure changes in the rock during burial of the sediments, but found all of the possibilities unlikely.
The haematite structures have the same characteristic branching of iron-oxidizing bacteria found near other hydro-thermal vents today and were found alongside graphite and minerals like apatite and carbonate which are found in biological matter including bones and teeth and are frequently associated with fossils.
They also found that the mineralized fossils are associated with spheroidal structures that usually contain fossils in younger rocks, suggesting that the haematite most likely formed when bacteria that oxidized iron for energy were fossilized in the rock.
"We found the filaments and tubes inside centimeter-sized structures called concretions or nodules, as well as other tiny spheroidal structures, called rosettes and granules, all of which we think are the products of putrefaction. They are mineralogically identical to those in younger rocks from Norway, the Great Lakes area of North America, and Western Australia," explained Dr. Dominic Papineau, also of the UCL Earth Sciences and the London Center for Nanotechnology.
"The structures are composed of the minerals expected to form from putrefaction, and have been well documented throughout the geological record, from the beginning until today. The fact we unearthed them from one of the oldest known rock formations, suggests we've found direct evidence of one of Earth's oldest life forms. This discovery helps us piece together the history of our planet and the remarkable life on it, and will help to identify traces of life elsewhere in the universe."
Matthew Dodd concluded, "These discoveries demonstrate life developed on Earth at a time when Mars and Earth had liquid water at their surfaces, posing exciting questions for extra-terrestrial life. Therefore, we expect to find evidence for past life on Mars 4,000 million years ago, or if not, Earth may have been a special exception."
UK Scientists Believe That Life is Continuously Entering Earth's Atmosphere From Space
By using balloons that were sent up into the stratosphere in 2013, scientists from the University of Sheffield in the UK believe they have found microscopic alien life forms that have arrived to Earth from space.
The team, led by Professor Milton Wainwright, from the University's Department of Molecular Biology and Biotechnology found small organisms that could have come from space after sending a specially designed balloon to 27km into the stratosphere during the recent Perseid meteor shower.
Professor Wainwright said "Most people will assume that these biological particles must have just drifted up to the stratosphere from Earth, but it is generally accepted that a particle of the size found cannot be lifted from Earth to heights of, for example, 27km. The only known exception is by a violent volcanic eruption, none of which occurred within three years of the sampling trip.
"In the absence of a mechanism by which large particles like these can be transported to the stratosphere we can only conclude that the biological entities originated from space. Our conclusion then is that life is continually arriving to Earth from space, life is not restricted to this planet and it almost certainly did not originate here."
Professor Wainwright said the results could be revolutionary. "If life does continue to arrive from space then we have to completely change our view of biology and evolution," he added. "New textbooks will have to be written."
The balloon, designed by Chris Rose and Alex Baker from the University of Sheffield's Leonardo Centre for Tribology, was launched near Chester and carried microscope studs which were only exposed to the atmosphere when the balloon reached heights of between 22 and 27km. The balloon landed safely and intact near Wakefield. The scientists then discovered that they had captured a diatom fragment and some unusual biological entities from the stratosphere, all of which are too large to have come from Earth.
Professor Wainwright said stringent precautions had been taken against the possibility of contamination during sampling and processing, and said the group was confident that the biological organisms could only have come from the stratosphere.
Professor Wainwright added "Of course it will be argued that there must be an, as yet, unknown mechanism for transferring large particles from Earth to the high stratosphere, but we stand by our conclusions. The absolutely crucial experiment will come when we do what is called "isotope fractionation." We will take some of the samples which we have isolated from the stratosphere and introduce them into a complex machine. A button will be pressed. If the ratio of certain isotopes gives one number then our organisms are from Earth, if it gives another, then they are from space. The tension will obviously be almost impossible to live with!"
Curiosity Rover Found Conditions Once Suited for Ancient Life on Mars
An analysis of a rock sample collected by NASA's Curiosity rover in 2013 showed that ancient Mars could have supported living microbes.
Scientists identified sulfur, nitrogen, hydrogen, oxygen, phosphorus, and carbon -- some of the key chemical ingredients for life -- in the powder Curiosity drilled out of a sedimentary rock near an ancient stream bed in Gale Crater on the Red Planet last month.
"A fundamental question for this mission is whether Mars could have supported a habitable environment," said Michael Meyer, lead scientist for NASA's Mars Exploration Program at the agency's headquarters in Washington. "From what we know now, the answer is yes."
Clues to this habitable environment come from data returned by the rover's Sample Analysis at Mars (SAM) and Chemistry and Mineralogy (CheMin) instruments. The data indicate the Yellowknife Bay area the rover is exploring was the end of an ancient river system or an intermittently wet lake bed that could have provided chemical energy and other favorable conditions for microbes. The rock is made up of a fine-grained mudstone containing clay minerals, sulfate minerals and other chemicals. This ancient wet environment, unlike some others on Mars, was not harshly oxidizing, acidic, or extremely salty.
The patch of bedrock where Curiosity drilled for its first sample lies in an ancient network of stream channels descending from the rim of Gale Crater. The bedrock also is fine-grained mudstone and shows evidence of multiple periods of wet conditions, including nodules and veins.
Curiosity's drill collected the sample at a site just a few hundred yards away from where the rover earlier found an ancient streambed in September 2012.
"Clay minerals make up at least 20 percent of the composition of this sample," said David Blake, principal investigator for the CheMin instrument at NASA's Ames Research Center in Moffett Field, Calif.
These clay minerals are a product of the reaction of relatively fresh water with igneous minerals, such as olivine, also present in the sediment. The reaction could have taken place within the sedimentary deposit, during transport of the sediment, or in the source region of the sediment. The presence of calcium sulfate along with the clay suggests the soil is neutral or mildly alkaline.
Scientists were surprised to find a mixture of oxidized, less-oxidized, and even non-oxidized chemicals, providing an energy gradient of the sort many microbes on Earth exploit to live. This partial oxidation was first hinted at when the drill cuttings were revealed to be gray rather than red.
"The range of chemical ingredients we have identified in the sample is impressive, and it suggests pairings such as sulfates and sulfides that indicate a possible chemical energy source for micro-organisms," said Paul Mahaffy, principal investigator of the SAM suite of instruments at NASA's Goddard Space Flight Center in Greenbelt, Md.
An additional drilled sample will be used to help confirm these results for several of the trace gases analyzed by the SAM instrument.
"We have characterized a very ancient, but strangely new 'gray Mars' where conditions once were favorable for life," said John Grotzinger, Mars Science Laboratory project scientist at the California Institute of Technology in Pasadena, Calif. "Curiosity is on a mission of discovery and exploration, and as a team we feel there are many more exciting discoveries ahead of us in the months and years to come."
Funnels on Mars Could Be the Place to Look for Life
A strangely shaped depression found on Mars in 2016 could be a new place to look for signs of life on the Red Planet, according to a study led by the University of Texas at Austin. The depression was probably formed by a volcano beneath a glacier and could be a warm, chemical-rich environment well suited for microbial life.
"We were drawn to this site because it looked like it could host some of the key ingredients for habitability -- water, heat, and nutrients," said Joseph Levy, a research associate at the University of Texas Institute for Geophysics, a research unit of the Jackson School of Geosciences.
The depression is inside a crater perched on the rim of the Hellas basin on Mars and surrounded by ancient glacial deposits. It first caught Levy's attention in 2009, when he noticed crack-like features on pictures of depressions taken by the Mars Reconnaissance Orbiter that looked similar to "ice cauldrons" on Earth -- formations found in Iceland and Greenland made by volcanos erupting under an ice sheet. Another depression in the Galaxias Fossae region of Mars had a similar appearance.
"These landforms caught our eye because they're weird looking. They're concentrically fractured so they look like a bullseye. That can be a very diagnostic pattern you see in Earth materials," said Levy, who was a postdoctoral researcher at Portland State University when he first saw the photos of the depressions.
But it wasn't until this year that he and his research team were able to more thoroughly analyze the depressions using stereoscopic images to investigate whether the depressions were made by underground volcanic activity that melted away surface ice or by an impact from an asteroid. Study collaborator Timothy Goudge, a postdoctoral fellow at the institute, used pairs of high resolution images to create digital elevation models of the depressions that enabled indepth analysis of their shape and structure in 3D. Researchers from Brown University and Mount Holyoke College also participated in the study.
"The big contribution of the study was that we were able to measure not just their shape and appearance, but also how much material was lost to form the depressions. That 3D view lets us test this idea of volcanic or impact," Levy said.
The analysis revealed that both depressions shared an unusual funnel shape, with a broad perimeter that gradually narrowed with depth.
"That surprised us and led to a lot of thinking about whether it meant there was melting concentrated in the center that removed ice and allowed stuff to pour in from the sides. Or if you had an impact crater, did you start with a much smaller crater in the past, and by sublimating away ice, you've expanded the apparent size of the crater," Levy said.
After testing formation scenarios for the two depressions, researchers found that they probably formed in different ways. The debris spread around the Galaxias Fossae depression suggests that it was the result of an impact... But the known volcanic history of the area still doesn't rule out volcanic origins, Levy said. In contrast, the Hellas depression has many signs of volcanic origins. It lacks the surrounding debris of an impact and has a fracture pattern associated with concentrated removal of ice by melting or sublimation.
The interaction of lava and ice to form a depression would be an exciting find, Levy said, because it could create an environment with liquid water and chemical nutrients, both ingredients required for life on Earth. He said that the Hellas depression and, to a lesser extent, the Galaxias Fossae depression, should be kept in mind when looking for habitats on Mars.
Gro Pedersen, a volcanologist at the University of Iceland who was not involved with the study, agrees that the depressions are promising sites for future research.
"These features do really resemble ice cauldrons known from Earth, and just from that perspective they should be of great interest," Pedersen said. "Both because their existence may provide information on the properties of subsurface material -- the potential existence of ice -- and because of the potential for revealing ice-volcano interactions."
Life as We Don't Know It
Over the years, NASA-funded astrobiology research has changed the fundamental knowledge about what comprises all known life on Earth.
Researchers conducting tests in the harsh environment of Mono Lake in California in 2010 discovered the first known microorganism on Earth able to thrive and reproduce using the toxic chemical arsenic. The microorganism substitutes arsenic for phosphorus in its cell components.
"The definition of life has just expanded," said Ed Weiler, NASA's associate administrator for the Science Mission Directorate at the agency's Headquarters in Washington. "As we pursue our efforts to seek signs of life in the solar system, we have to think more broadly, more diversely and consider life as we do not know it."
This finding of an alternative biochemistry makeup will alter biology textbooks and expand the scope of the search for life beyond Earth.
Carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur are the six basic building blocks of all known forms of life on Earth. Phosphorus is part of the chemical backbone of DNA and RNA, the structures that carry genetic instructions for life, and is considered an essential element for all living cells.
Phosphorus is a central component of the energy-carrying molecule in all cells (adenosine triphosphate) and also the phospholipids that form all cell membranes. Arsenic, which is chemically similar to phosphorus, is poisonous for most life on Earth. Arsenic disrupts metabolic pathways because chemically it behaves similarly to phosphate.
"We know that some microbes can breathe arsenic, but what we've found is a microbe doing something new -- building parts of itself out of arsenic," said Felisa Wolfe-Simon, a NASA Astrobiology Research Fellow in residence at the U.S. Geological Survey in Menlo Park, Calif., and the research team's lead scientist. "If something here on Earth can do something so unexpected, what else can life do that we haven't seen yet?"
The newly discovered microbe, strain GFAJ-1, is a member of a common group of bacteria, the Gammaproteobacteria. In the laboratory, the researchers successfully grew microbes from the lake on a diet that was very lean on phosphorus, but included generous helpings of arsenic. When researchers removed the phosphorus and replaced it with arsenic the microbes continued to grow. Subsequent analyses indicated that the arsenic was being used to produce the building blocks of new GFAJ-1 cells.
The key issue the researchers investigated was when the microbe was grown on arsenic did the arsenic actually became incorporated into the organisms' vital biochemical machinery, such as DNA, proteins and the cell membranes. A variety of sophisticated laboratory techniques was used to determine where the arsenic was incorporated.
The team chose to explore Mono Lake because of its unusual chemistry, especially its high salinity, high alkalinity, and high levels of arsenic. This chemistry is in part a result of Mono Lake's isolation from its sources of fresh water for 50 years.
The results of this study will inform ongoing research in many areas, including the study of Earth's evolution, organic chemistry, biogeochemical cycles, disease mitigation and Earth system research. These findings also will open up new frontiers in microbiology and other areas of research.
"The idea of alternative biochemistries for life is common in science fiction," said Carl Pilcher, director of the NASA Astrobiology Institute at the agency's Ames Research Center in Moffett Field, Calif. "Until now a life form using arsenic as a building block was only theoretical, but now we know such life exists in Mono Lake."
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