by Marc Kaufman
During the Mount St. Augustine eruption, Thomas teamed up with Alaska Volcano Observatory scientist Steven McNutt, who had initially noticed the heavy lightning associated with the event. When Mount Redoubt was preparing to go off, McNutt contacted Thomas, who rushed up to Alaska’s Kenai Peninsula to set up the antennas that would monitor the eruptions. His technique was simple but novel: He was going to collect radio waves from the erupting volcano, which would contain the information he needed about the lightning being discharged in and above the volcano. Especially early during an eruption, ash and rock can hide the lightning, and those early fireworks seemed to be the most interesting. Their team set up a Lightning Mapping Array with four stations two months prior to what turned out to be a delayed eruption. Each station, explained one team member, has “basically a simple TV antenna set to pick up channel three—the frequency that lightning radiates.”
When the volcano first blew in late March 2009, the instruments set up by Thomas and his colleagues found that lightning flashes accompanied every single one of the more than twenty major eruptions that occurred over thirteen days. What’s more, they detected an unusual kind of lightning in the early moments of the eruption: a “constant lightning” that contained an extraordinarily high number of short bursts of 40 to 100 feet. They’ve never actually been seen, but Thomas imagines they would dance like enormous sparks from a monumental spark generator. The energy being released was monumental, a mass of very large electrical sparks that, if similar to other recent observations of constant lightning, glowed orangered at the peripheries and a deeper red close to the mouth. Thousands of small flashes each set off radio impulses that flew across the inlet and were captured by the waiting receivers, which then drew a picture in graphs of what was happening. “The really intense phase of constant lightning went on for twenty to thirty minutes,” Thomas told me. “We saw more lightning than we’d generally see in a major thunderstorm.” His fellow researcher McNutt said those lightning strikes at the start of the Redoubt eruption lasted only 1 to 2 milliseconds and were “a different kind of lightning than had ever been seen before.” Quite obviously, a great deal of energy was being released, exactly what was needed to “spark” the gases and water erupting from the volcano and change them in ways that would produce amino acids.
The radio monitors set up by Thomas’s team were all on the far side of robin’s-egg-blue Cook Inlet, about forty miles away from Mount Redoubt. They had wanted to place them closer, but the combination of Redoubt’s location on protected federal land and the obvious dangers of being too near the volcano made that impossible. By correlating the millisecond differences in their flashes and triangulating the distances from the radio monitors across the inlet, Thomas was able to map and measure the lightning strikes inside the ash clouds in a new way—showing where the lightning originated and how it spread. He had begun that kind of monitoring at the Mount St. Augustine eruption in 2006 and had seen some of the same phenomenon, but it was during the Mount Redoubt eruption that the “constant lightning” phase was confirmed and better characterized. For a man who has witnessed a lot of lightning, Thomas was impressed. “I’m not sure I’ve ever been so excited by lightning before,” was his conclusion.
As the team waited for possible further eruptions, McNutt proposed a trip to the mouth of the still-steaming volcano in a small, six-seater airplane. We approached ten-thousand-foot Mount Redoubt from the back, and were promptly introduced to the volcano mouth, hissing and spitting a short distance from the peak. From some angles, the volcano still appeared to be smoldering inside with a yellow-orange glow. Not surprisingly, we tend to think of volcanoes in terms of the dangers posed by shooting rock and flowing lava, noxious smells, ash shower, and acid rain—the effects we can see on the Earth’s surface and its creatures. But flying over the still-scalding mouth and the lava slide forming just below, volcanoes come across as the endpoint of a tortured pathway from the innards of the Earth up to the surface. They deliver molten rock as hot as 2,000 degrees Fahrenheit and high-pressure gases from a place that seldom enters our minds: the rocky mantle below the Earth’s crust, where the frictions and pressures of the always jostling continental plates, combined with the heat emanating from the planet’s liquid outer core, can become so intense they, well, melt rock. Even a clouded peek into that world is unsettling; the power is just so unimaginable. Getting an up-close glimpse of the power and magnitude of a volcano—even without its supercharged lightning bursts—made the kind of early Earth chemistry proposed by Miller seem entirely possible.
As we circled the volcano, we could also see a thin, cloudlike haze and plumes above the peak of what looked like a gigantic steam grate at the volcano’s mouth. The haze, Thomas and McNutt explain, is sulfur dioxide (which erupts with the magma and can lead to damaging acid rain) and the plume is largely H2O. Magma contains huge quantities of water—more than in a thunderstorm, Thomas said—released during the melting of the rocks. If the airplane windows were opened, we would also have smelled the rotten-egg odor of hydrogen sulfide and would have been bathed in methane and nitrogen as well. The violence of a volcano’s eruption is largely a function of the gases present; through their natural expansion, they determine just how explosive the eruption will be based on what gases are present and in what quantities they concentrate. But the gases that emerge are not necessarily the gases that settle on the surrounding landscape. The great temperature and pressure changes at eruption and all those lightning bolts of highly charged electricity set off chemical reactions that modify or transform the gases. That’s the cascade of changes that Stanley Miller identified decades ago, and that Bada and his colleagues recently found to be even more enhanced in Miller’s initially unpublished but now available experiment designed especially for volcanic conditions.
Earth has always had volcanoes of all kinds and in all climates: Volcanologists estimate there are about six hundred active ones today, and believe there were many more in the distant past (and on other planets like Venus and Mars). Some of those Earthly volcanic ranges, including the ones that formed the Hawaiian Islands and Iceland, bring up gases more directly from the scalding outer core, lessening their time in the cooling mantle. They also provide the kind of protective micro-environments that Bada and Lazcano believe played a major role in the origins of life, when much of the globe was covered in oceans only dotted with volcanic islands. The building blocks for the formation of amino acids and then proteins were all there, and Miller and his disciples showed in the lab a pathway for the process to work. We will never know for sure how that initial transformation from nonliving to living occurred because the evidence is gone. But we can know how the building blocks were formed from simpler, more elemental molecules.
Several months after Mount Redoubt calmed down, Bada came across some other potentially interesting vials in the old Miller cache. The one that most intrigued him was the brown residue produced by another experiment in 1958, one that used different gases than the original iconic Miller-Urey experiment. The 1958 model eliminated the hydrogen and added carbon dioxide, thereby responding to critics who said Miller was using the wrong gases to replicate atmospheric conditions on the early Earth. Miller also added the foul-smelling hydrogen sulfide that generally accompanies volcanic explosions and again sparked the mix with lightning-like electricity. The results, Bada said, were even more remarkable than the earlier experiments—with a greater number of amino acids produced and a better lineup of isomers, compounds with the same molecular formula but with different structures.
“I stand back and look at what’s happened and I’m still dumbstruck,” Bada said. “We’ve had the results of these experiments for at least ten years yet we never knew they existed. It’s incredible new information and really shows Stanley’s influence is with us today.”
Antonio Lazcano, Bada’s longtime colleague and current collaborator in testing more of Miller’s vials, added this footnote: Asked why Miller never published the robust results from the ex
periment that added the hydrogen sulfide, Lazcano gave a very human, if scientifically questionable, reply. “Stanley always said he hated the rotten-egg smell of the hydrogen sulfide,” he said. “I think he just didn’t want to be around it.”
The legacy of Stanley Miller is now very much living again not only because of the newly found volcano results, but because he trained men like Bada and Lazcano, who in turn have trained or mentored biochemists and astrochemists such as Glavin and Dworkin. They are the golden boys of NASA’s Goddard Space Flight Center, located outside Washington, D.C., who used their cachet to lobby for a new generation of high-powered instruments that can analyze chemical and biological specimens—including the rediscovered Miller-Urey material—and map their electromagnetic fingerprint (and thus their chemical makeup) with greatly increased precision. They use their new tools to study the building blocks of life in meteorites, in comets, and in the vastness of space, and they have taken the origins-of-life field in some surprising new directions. One of their focuses has been on the peculiar dynamics of chirality—the uniform and unusual “handedness” of proteins and sugars—a phenomenon as puzzling as it is potentially revelatory. It’s a tricky concept to take in, but basically involves the logic of mirror images: entities with the exact same structure, but set in an opposite direction.
Scientists have worked for decades to understand chirality, which has applications in drug-making and could someday be important in determining whether a microbe found on Mars or Europa or a comet is related to life on Earth or has an entirely separate origin. But it’s virtually unknown to most everyone else. Here’s a quick introduction:
In the mid-nineteenth century, the renowned microbiologist and chemist Louis Pasteur took on one of the puzzles of the day: why a solution with tartaric acid derived from living things (in this case, the discarded yeast remains of the winemaking process) behaved differently from a solution with the same tartaric acid that had been made synthetically. The difference involved how light passed through the liquid. The light entering the biologically derived solution didn’t go straight through but rather was refracted off to one side, while the chemically synthesized sample allowed the light to pass through unchanged. Pasteur grew crystals of a compound including the tartaric acid and noticed that they came in two nonsymmetric forms that were nonetheless mirror images of each other. He laboriously separated the two forms of the compounds and found that solutions of one form rotated light clockwise while the other form rotated light counterclockwise. If the solution had an equal mix of the two versions of the molecule, then there was no effect on the light at all. What Pasteur correctly made of this is that the molecules of tartaric acid could exist in either a “right-handed” or “left-handed” form, rather like left- and right-handed gloves. The left-handed version was always biological, the right-handed one always synthesized.
I met Glavin and Dworkin one morning to learn about the unlikely role of chirality in astrobiology. They are astrobiologists now, but have backgrounds in physics, planetary sciences, and astrochemistry. Our destination was the Smithsonian’s National Museum of Natural History and its collection of meteorites in a gallery called “Geology, Gems and Minerals.” To be precise, meteorites don’t fit any of those listed categories. But among the incoming rocks on display are the Allende meteorite from Mexico, the Orgueil meteorite from France, the Murchison meteorite from Australia—all legendary in the world of meteorites, and of especially great interest to astrobiologists. You couldn’t tell by looking at it, or by gauging the pedestrian display or reading the brief description, but the dark gray Murchison meteorite in particular has become something of a holy grail for astrobiology. That’s why Glavin, Dworkin, and other researchers come to the museum to collect precious samples stored away in a collection room closed to the public and filled with bagged and preserved pieces of Murchison and other rocks arrived from space. Of all the meteorite samples in the vast Smithsonian collection, about one quarter of the requests for samples are for a small piece of Murchison.
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Pieces of Murchison hardly look remarkable now, and would be easy to ignore if you passed them by on the ground—just another faded dark gray rock with some shinier white highlights inside. But when it burned through the atmosphere in 1969 and landed in the Australian countryside, it was a gift from beyond. The roughly two hundred pounds of meteorite, broken up into rocks large and small, were collected with unusual speed, and in some cases protected from contamination. (In other cases, contamination is a greater issue—including the pieces that fell in a barnyard and were tossed by the farmer into the microbe-filled manure heap.) In the years that followed, hundreds of scientific papers have been written based on the ancient geochemical treasures found inside Murchison.
What makes it so important is that it is an extremely rare meteorite with lots of organic carbon (as opposed to the many others made up primarily of iron, nickel, silicon compounds, or inorganic carbons like graphite), and so is an extraterrestrial laboratory for the kind of carbon-based chemistry that ultimately produces life on Earth. To the initial amazement and delight of researchers, Murchison was found to be loaded with some of the important and complex molecules needed for life—including some of those amino acids that are used to make proteins. Just as English words are made up of the twenty-six-letter alphabet, all proteins—the workhorse molecules of life—are made up of twenty of the hundreds of amino acids known or suspected to exist. About half of those twenty amino acids essential for biology on Earth were found in Murchison. What does this mean? It does not mean what may first come to mind—that the presence of those biological amino acids says the rocks once were home to living things. Rather, it’s the fact that only half of the twenty protein amino acids have been found. The absence of the rest has been used to bat down charges that the meteorite was substantially contaminated by Earthly microbes. If the rocks had been widely contaminated, then all the Earth’s biological amino acids would be present. In addition, Murchison has scores of other amino acids found on Earth but unassociated with life and many others with no known Earthly counterparts. All of those complex molecules, it had to be assumed, were formed from simpler elements while on asteroids, comets, or in the primordial cloud of dust and gas where the solar system was born—making Murchison a true Rosetta stone sent down from space.
Here’s where it gets really interesting to Murchison researchers. On Earth, virtually all living cells containing amino acids (and therefore proteins) are entirely “left-handed.” Virtually all have sugars of a molecular structure deemed to be entirely “right-handed.” This works great for biology, because the proteins and sugars need to be of opposite structures to successfully interact. But this kind of “homochirality,” with virtually all proteins and sugars structured entirely in the same way, is unique. Everything else that isn’t biological on Earth contains molecules that are mixed right-handed and left-handed in roughly the same proportion. Rocks, water, inorganic chemical solutions—they all have molecules that are mixed right- and left-handed on Earth and, as far as we know, everywhere else. Yet somehow the proteins and sugars essential to life are significantly abnormal in a way that makes biology possible. Dworkin put it like this: Biology would still work fine if amino acids were all right-handed rather than all left-handed, but wouldn’t work at all if they were mixed left and right. “If you mix them, life turns into something resembling scrambled eggs—it’s a mess. Since life doesn’t work with a mixture of left-handed and right-handed amino acids, the mystery is how did life decide—what made life choose left-handed amino acids over right-handed ones?”
The mystery remains unsolved, but scientists have been finding clues to help explain it. And a primary repository of those clues is the Murchison meteorite. The pioneering work was done in the mid-1990s by two biochemists at Arizona State University, Sandra Pizzarello and John Cronin. The two isolated one particular amino acid called isovaline from Murchison, concentrated it, and then did an analysis of its chirality. Sin
ce everything nonbiological was understood to have molecules equally left- and right-handed, the assumption had to be that the isovaline would also be equally mixed. But it was not. The imbalance wasn’t great, but there were about 8 percent more left-handed isovaline molecules than right-handed ones in Murchison. The discovery opened the door to several remarkable possibilities: that forces in the cosmos could transform the handedness of some molecules traveling through space on meteors, asteroids, or even dust, and that the handedness could then be gradually exaggerated on Earth until—in the case of the twenty amino acids essential for life—that small excess would become complete left-handedness.
Glavin and Dworkin used their more sophisticated instruments a decade later to make similar measurements of isovaline from Murchison and other meteorites. What they found was similar but more pronounced: a left-handed excess of 18 percent. Since no other nonbiological molecules on Earth are known to have this kind of excess, the two concluded that the left-handedness of amino acids, proteins, and therefore life on Earth most likely came from beyond. That hypothesis is now broadly accepted.
Meteorites bombarded the Earth 4 billion years ago and they delivered an impressive amount of carbon-based material to Earth, something on the order of hundreds of thousands of tons per year. The infall is much smaller now, on the order of 5,500 tons per year and most in the form of micrometeorites or even smaller particles of interplanetary dust. So how did those space-faring amino acids develop their slight excesses of left-handedness? Long-term exposure to the cosmic radiation of neutron stars is the most likely explanation, since chirality has been shown to change slightly when exposed to certain kinds of highly energized light. But no firm consensus has yet produced an answer.