When I finally sit down with Dalgarno, the Phillips Professor of Astronomy, I find myself with an extremely genial eighty-two-year-old with prominent fly-away, bright-white eyebrows. He is slouched slightly forward in a wooden chair, its arms worn smooth with use. He wears a herringbone jacket that he keeps in his office and sensible black loafers. The spark in his eyes is a reminder of an earlier time, when Dalgarno, had he put more effort into soccer than into mathematics, might have had a career with England's Tottenham Hotspurs, with whom he was invited to try out. Few outsiders now come looking for Dalgarno, and those who work here know where to find him; he's been a fixture at Harvard since 1967. Along with this impressive tenure, he's had the ultimate insider's view on the development of late twentieth-century astrophysics as editor for three decades of one of the field's premier scientific journals, the Astrophysical Journal Letters.
As such, Dalgarno is both professionally and personally a bridge to earlier times. Born in 1928, he recalls listening to astrophysicist Fred Hoyle's famed BBC broadcasts in the late 1940s and, during his first academic posting in the late 1950s, seeing Hoyle lecture in Dublin, Ireland, where he won over a rowdy group of students with his intense presence and broad speculation on everything from the origin of the elements to the origin of everything. “Of course, half of it wasn't true,” Dalgarno says with a chuckle. However, the half that was true, the part that fueled the astronomer's periodic table, has guided Dalgarno's career. Dalgarno has always loved tackling puzzles of all kinds, and he was drawn to the mother of them all. He's one of the founders of the field of molecular astrophysics, or cosmic molecular evolution—the study of how the universe has evolved its present chemical complexity. In simple terms, if you feel that the universe is getting more complex all the time, Alex Dalgarno has proven you right.
When it comes to the cosmos’ chemical evolution, Dalgarno has probably spent as much time as anyone in the history of the planet thinking about the universe's most basic element: hydrogen. He's studied hydrogen as an ion and as a molecule; he's studied its isotopes, its quantum states, and its optical properties. The amazing thing is that he's considered hydrogen not so much to understand this tiniest atom but to understand the essence of the entire cosmos. The doorway to understanding the full complexity and expanse of the observable universe is through its simplest atomic constituent—which makes Dalgarno perfectly suited to think about the very beginnings of time, when hydrogen was just about the only elemental word the newborn universe could utter. “In the beginning,” he says, “there were no atoms or molecules…. It was an unpromising scenario for the formation of complex structures like galaxies; black holes; stars; planets; nuclear, atomic, and molecular systems; and living organisms.” Just as looking at newborn baby pictures often leaves us amazed to think that that little, reddish, prune-faced thing will grow up to be a suit-wearing banker pulling in a six-figure income, so, too, does the newborn universe appear almost unrecognizably different from what it will become. Perhaps the most revolutionary insight of the astronomer's periodic table is that, for approximately the first two hundred million years in the infant universe, across all its vastness, there wasn't a single atom heavier than beryllium, not a single atom of carbon, nowhere the glitter of gold.
The short version of big-bang nucleosynthesis—the formation of the first atoms—might sound familiar to many couples: about fifteen minutes of intense procreative activity followed by a two-hundred-million-year lull in atom-making, most of it spent in darkness. At its first breath, the cosmos was unrecognizable to everyone except particle physicists. The universe emerged with such energetic fury that only the fundamentally indivisible particles, the quarks and electrons, could survive intact, bathed in a sea of intense radiation. The newborn cosmos was dense, gassy, and unimaginably hot, too hot for matter to stick together; there was nothing solid or liquid. Particles collided with such force that they ricocheted rather than bonded or fused. But as the universe expanded, creating time and space, it also cooled. After just one second, slightly less energetic quarks congealed into the more familiar neutrons and protons that form the nuclei of atoms. Within three minutes (astrophysicists clock it to about two hundred seconds, less time than it takes most of us to shower), the growing cosmos’ temperature had fallen to under two billion degrees Fahrenheit. At this temperature, the cosmos experienced its first burst of nuclear building, or big-bang nucleosynthesis. Though most protons stayed single, a quarter by mass of all the baryonic matter (the stuff we see as matter, excluding dark matter) was forged into helium nuclei—two protons and two neutrons—and tiny amounts of lithium and beryllium, the next two elements on the periodic table. After fifteen minutes, this first act of heated creation was over. But the growing universe was still so hot, and thus energetic, that these nuclei couldn't hold onto a single electron; they were fully ionized. For about four hundred thousand years, says Dalgarno, the universe “coasted along” in this ionized state, expanding and cooling.
Then, like a baby's first smile, something truly new happened in the life of the cosmos: the first fully formed atoms were born. The expanding cosmos had cooled enough that, one by one, across space and time, when a positive nuclei and an electron collided, they didn't deflect like colliding billiard balls but stayed bonded together to form the neutral atoms of hydrogen and helium. Astrophysicists call it the Recombination Era; though the term recombination is a misnomer, since these negative and positive particles were never previously combined. With neutral atoms came a crucial evolutionary stage. The infant cosmos took its first chemical baby steps. As Dalgarno describes it, through a series of collisions between helium and hydrogen atoms energized by bountiful electrons and photons, most lone, neutral hydrogen atoms joined to become molecular hydrogen. These were the cosmos’ first atomic bonds, and with them came the introduction of a new cosmic form: the molecule. With this step, the cosmos gradually went dark. Molecular hydrogen is a gassy curtain, opaque to visible wavelengths of light. To the human eye, the universe was completely dark for its first hundred million years—hence the Recombination Era's other name, the Dark Ages.
Where others see darkness, however, Dalgarno sees something else: the dawn of chemistry. Molecular hydrogen paved the way for the creation of a vastly expanded cosmic alphabet, one that could articulate the language of life. “The introduction of the neutral hydrogen molecule was a crucial step in the evolution of the universe,” he says. It was only out of darkness that light could emerge. It was only because the cosmos went dark that the next evolutionary step could take place. Star formation depends on atoms’ and molecules’ abilities to radiate away the heat from gravitational collapse, and molecular hydrogen was the antifreeze of the early universe. Without it, the first stars couldn't be born almost two hundred million years later, in the era of cosmic dawn, now one of the most sought-after epochs in cosmic history. With the birth of the stars came an exponential bump in the nature of cosmic chemistry, the forging of a panoply of elements from carbon to uranium. These elements, in turn, found partners to create previously unseen types of unions, and they filled the universe with a new vocabulary of molecules such as carbon monoxide and formaldehyde—the building blocks of organic chemistry—and minerals, including sandy silicon dioxide, the crystalline beginning of rocky planets.
“I'm afraid I haven't been of much help,” Dalgarno says with a smile and a shrug as I turn off my microphone and prepare to leave his office. He's referring to my quest to find the intellectual intersection of biology and astronomy. He's an astrophysicist; he doesn't feel comfortable leaving the realm of firm, testable numbers and equations. Linnaean Street might be a baseball's throw away, but biology is a foreign land, a foreign language. Yet Dalgarno's insights are central to the Stardust Revolution. With a physicist's penchant for exacting detail, he helped open the door to the conceptual framework that the cosmos isn't just expanding; it's growing more chemically complex in a process of cosmic evolution. Dalgarno is typical of many of the key protagonists in the S
tardust Revolution: each has contributed a detailed piece—some small, some large—of a grand puzzle, often with little or no initial inkling of the larger picture to which they were contributing.
In documenting the emergence of cosmic chemical complexity, of a cosmos replete with large carbon-based molecules emerging from a simple soup of hydrogen and helium, Dalgarno and others have shifted the notion of the big bang from one relating to the origins of the physical universe to the story of a biological big bang. The tale he recounted to me in his office is usually heard as the crowning achievement of twentieth-century cosmology and astrophysics, joining the birth of the visible universe, of time and space, from the quantum nature of atoms to the grand architecture of the cosmos. The story Dalgarno tells is, however, a different one; it is as if a second narrator takes the stage in a Shakespearean drama and provides the audience with another view of the very same events. Dalgarno's version leads not to the nature of galactic structure nor to the dynamics of pulsars but to something much more deeply mysterious: life. In documenting the emergence of molecular complexity, he has mapped the thin, tendril-like roots of our cosmic family tree. He has helped join Darwin and the cosmos.
In the halls of the CfA today, Linnaeus has been given a central place. His term homo, for man, is derived from an ancient proto-Indo-European word meaning “earth” or “ground.” Now the wise man of the Earth is wondering what shared characteristics tie him to the stars. At the CfA, astrophysics and biology have been joined in its Origins of Life Initiative, led by Dalgarno's CfA colleague Dimitar Sasselov, an astronomer turned astrobiologist. For Sasselov and his network of astronomers, physicists, chemists, and biologists, the search for an alien Earth—a living planet around a distant star—and synthetic biology—the ultimate goal of which is to make life in the lab from scratch—are intrinsically connected as part of the same question. The program's goal, according to Sasselov, is “a revolution in our understanding of life, and its place in the cosmos.”
As Harvard's Origins of Life Initiative exemplifies, the Stardust Revolution is about much more than finding a single other instance of alien life. It's about developing a universal understanding of life and its origins and cosmic distribution. It's about understanding how Darwinian evolution can be extended, or embedded, in the breadth of cosmic evolution extending from the origin of the elements in stars, to cosmic chemical evolution, to the emergence of solar systems, and—of most interest to us—to the origins of life in this cosmic context. When we seek our origins, we follow the tree of life that connects us not just back to distant ancestors on Earth but also to everything else in the cosmos, allowing us to develop an understanding of life as an emergent weave from the atoms forged in stars to the birth of a child. At the heart of this pursuit, the tracing of our family tree back to a time before the first life on Earth or even before the Earth itself, is a truly extreme genealogical question: What is life?
WHAT IS “LIFE”?
The most interesting insights at science conferences, in my experience, occur during coffee-break kibitzing. The biennial NASA Astrobiology Science Conference, held in League City, Texas, in April 2010, was a stellar example of this. During the conference—held just down the road from NASA's Johnson Space Center, where ground controllers guided the Apollo missions to the Moon and back—numerous presentations profiled the latest research results on the cosmic origins of life and the ways in which alternately some terrestrial life was later obliterated by cosmic collisions. What I didn't know then was that many of the learned astronomers, biologists, chemists, and geologists were avoiding one question in the way an attentive driver avoids a pothole: What, exactly, is life?
I encountered this intellectual road hazard only during a coffee break, when I found myself standing beside a friendly thirtysomething NASA engineer. We shared tidbits about home and family, and then I asked him what he did. He replied that he was developing science-on-a-chip tools that could chemically identify the presence of life for future NASA robotic missions to Mars and possibly to other Solar System bodies. I asked him what his sensor would search for, what he thought life was. He smiled broadly and replied, “Life is love.” At first I thought he was avoiding the question or perhaps that he was being philosophical or folksy. He was doing a little of each, but he was also being completely honest. Although his answer wasn't the stuff of scientific journal articles, “Life is love” is in some ways as good an answer as anyone can provide. If love is the force of attraction between two beings or objects, then we view a cosmos as being defined by love from its first moments—quarks rushing to one another, hydrogen atoms bonding, helium atoms fusing, stardust joining to form planetesimals; all this great coming together.
In the Stardust Revolution, our understanding of life is getting a cosmic makeover. As astrobiologists consider the detailed origins of life on Earth and search for it elsewhere in the cosmos, the deeper problem they face is not how life starts but what life is. How will you know that you've found what you're looking for if you don't know exactly what you're looking for? What's so seemingly obvious—whether something is either alive or dead, an observation reminiscent of the great Monty Python “dead parrot” skit—is in fact the greatest conundrum to astrobiologists. This in itself is interesting. The weird thing about life, about biology, is that it's based on chemistry and physics. Physicists look for as-yet-undetected particles, but they're not wondering, “What is a particle?” There's matter and energy, and they just are. And chemists deal with the stuff of physicists, connecting atoms together to form molecules.
Yet for biologists, there's a big, usually unspoken of hole in the progression of things. At some point in the cosmic story of matter, magic seems to enter the equation in the form of life. How else can you explain going from stuff to life? Filling in this gap in our cosmic story is the grand challenge of twenty-first-century science. It's one that's very personal, when we consider that we are life, and thus the question could just as well be asked, “What am I?” The Stardust Revolution is a quest that is no longer the domain of only, or even primarily, biologists—of those who study what used to form the boundaries of “life”—it also involves chemists, physicists, astronomers, and mineralogists, among others. To understand the fundamental nature of life, these scientists are turning to molecular fossils and synthetic cells—and they're looking to the stars.
Fortunately, Steve Benner was also at the Astrobiology Science Conference in Houston. Benner thinks about, experiments on, and argues about the universal nature of life in the way that other guys get wrapped up in the details of old Ford® pickup trucks—which, if you've never talked with old-truck aficionados, is obsessively and in great detail. Sporting a frothy mop of blondish hair and radiating energy, Benner has a youthful pluck combined with serious smarts and curiosity that make him a natural intellectual scrapper. He's been brought to this conference to debate the origins of life and does so with humor and insight, even as his co-debater tosses audible backstage jibes during Benner's presentation. It's a disposition that's also given Benner, a chemist, the gumption to continually step outside the bounds of what most others think are the limits of the field.
Working in Harvard University's chemistry department in 1984, Benner veered from his planned research to complete the then-outlandish idea of the first chemical synthesis of a gene that encoded an enzyme—a protein that catalyzes other reactions. In other words, his lab group built a string of DNA that was the chemical blueprint for an enzyme. In so doing, Benner helped to found the now-booming field of synthetic biology, a field that looks at building life the same way a garage mechanic rebuilds an engine from its constituent parts. The difference, of course, is that synthetic biologists are trying to build “engines” that in turn make baby engines by themselves—baby engines that, over generations, also evolve. Benner developed ways to resurrect ancient proteins from extinct organisms, a process once thought of as a branch of science fiction but that is now the fruitful field of paleogenetics. According to Benner, despit
e all this innovation, he was threatened with the loss of his US government funding from the National Institutes of Health for not focusing on his proposed research agenda. As a result, he accepted a no-holds-barred position at Zurich's Swiss Federal Institute of Technology, one of the world's top research universities and former home to Albert Einstein, as well as to twenty-one other Nobel laureates.
In his work at Harvard, Benner had become intrigued with how molecular aspects were connected to whole-organism evolution—with the evolutionary links between molecules and life. At that time, he says, “I was the only chemist in the world interested in evolution.” Once again, however, those paying the bills thought Benner was outside the bounds of his discipline. Evolution was for biologists, said colleagues in Zurich, who told him that combining evolution and chemistry was nicht salbre, or intellectually dirty. But the time in Zurich gave Benner the space to develop the framework that now guides his research at his own institute in Gainesville, Florida, the Foundation for Applied Molecular Evolution, whose acronym—FfAME—perhaps speaks to Benner's larger ambitions. At FfAME, Benner is after nothing less than an understanding of life not just as we now know it but also as a universal phenomenon. About 170 miles northeast of Cape Canaveral, Benner is working to bring our understanding of life's fundamental nature into the space age. To do this, he and the dozen and a half other FfAME researchers are taking an integrated, four-part approach to understanding life as a universal concept, one that represents the spectrum of ways other stardust scientists are tackling the question.
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