J O H N F. M A R R A
HOT CA R BON CA R BON-14 a n d a R EVOLU T ION i n SCI ENCE
PREFACE
“S
eldom has a single discovery in chemistry had such an impact on the thinking in so many fields of human endeavour. Seldom has a single discovery generated such wide public interest.” So declared the chair of the Nobel Committee, quoting one of the nominating scientists, in awarding the 1960 Nobel Prize in Chemistry to Willard Libby for his method of age determination using carbon-14. A year later, Melvin Calvin received the Nobel Prize in Chemistry for unraveling the path of carbon fixed in photosynthesis. The presentation speech for Calvin’s Nobel noted that “photosynthesis is the absolute prerequisite for all life on earth and the most fundamental of all biochemical reactions,” adding that “the radioactive carbon isotope, 14C, well-known also in other connections, has played a particularly important role.”1 The stories surrounding the discovery and applications of carbon-14 in the second half of the twentieth century are the subject of this book. R. J. Gordon, in his Rise and Fall of American Growth: The U.S. Standard of Living Since the Civil War, notes that, except in the rural South, the daily life of every American changed beyond recognition between the end of the Civil War and the end of the Great Depression. By the end of World War II and the beginning of the so-called atomic age, the daily life of all Americans had changed profoundly. Carbon-14 is part of that sea change in outlook and life, and one of the most significant products of the atomic age. Despite being so worthy of attention, however, the role of carbon-14 became submerged, except in scientific circles. Biological metabolic cycles, displayed on wall charts, never reference the isotope that allowed
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those transformations to be portrayed. The popular press refers to “carbon dating” or “carbon dates” without noting the long-lived radioisotope that makes fixing those dates possible. Much research in oceanography involves carbon-14, but this is not among the topics that inspire colorful documentaries on public television. I hope with this book to uncover some of the secrets involved in the history of carbon-14. Stories of the impact of carbon-14 on daily life are told here quasichronologically, culminating in a continuing relationship with humanity and its advancement. I begin with the discovery of carbon-14 at the Berkeley Radiation Laboratory (chapters 1 and 2), then consider the discovery of radioactivity itself and how it is measured (chapter 3). Not long after the discovery of carbon-14 in the lab, it was found to be produced in the upper atmosphere, naturally and continuously. Chapter 4 describes how the natural occurrence of carbon-14 allows the dating of anything that accumulates carbon during its lifetime, tracing Willard Libby’s early efforts to establish the method. Chapter 5 recounts the history of the study of photosynthesis, and chapter 6 tells how Melvin Calvin and his team, in the late 1940s, worked out how carbon dioxide, via photosynthesis, is assimilated into organic matter. Chapter 7 returns to the assessment of carbon-14 (covered initially in chapter 3)—in particular, the inception of accelerator mass spectrometry (AMS), without which radiometric dating using carbon-14 would be next to useless. Chapter 8 then discusses various applications of carbon-14, using AMS, in dating archeological and other historical relics, the peopling of North America, and the age of human remains at archeological sites. In chapters 9 and 10, I consider circulation in the deep ocean as it was worked out in the 1980s, the Earth’s carbon cycle, and how the carbon cycle affects Earth’s climate. Chapters 11 and 12 review the problem of ocean productivity. In chapter 11, I jump back to the late 1940s and early 1950s to reappraise the introduction of carbon-14 to biological oceanography. I cover the early debates (still continuing today) about the ocean’s productivity and what led to the project “Plankton Rate Processes in Oligotrophic Oceans,” the topic of chapter 12. That project, in the mid-1980s, resulted in a paradigm shift in the study of ocean productivity—its magnitude and its importance to the Earth’s carbon cycle and ocean resources. I saved the study of carbon-14 and climate for chapter 13. Deciphering
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climate conditions since the last deglaciation, which is about the limit for the application of carbon-14, began in earnest in the late 1980s and spilled over to the twenty-first century. New data and ideas are rife at present, being generated almost monthly. As long as carbon constitutes the stuff of life on planet Earth, carbon-14 will find application. Carbon is what we’re made of. Carbon is life. It is fundamental also to how we live, how we interact with the Earth’s spheres, how the Earth is habitable—pretty much everything. And since the discovery of a long-lived radioisotope of carbon, we have an amazing tool to delve into almost every aspect of existence on Earth—and perhaps the universe. Sir James Jeans, an early-twentieth-century physicist and astronomer, once said, “Life exists in the universe only because the carbon atom possesses certain exceptional qualities.” What we’ll find in this book is that carbon-14 is ubiquitous; it can be measured everywhere life occurs, or has left an imprint. Ubiquity is both a good and a bad thing, scientifically. Teasing apart the variables and drivers, we find that, in most cases, the uses of carbon-14 with the clearest results are those in which carbon-14 is added to a system in comparison with distributions that occur naturally. An exception is the use of carbon-14 in dating archeological artifacts, although here, too, corrections have to be applied, and these become a science in themselves. For myself, I was part of perhaps the last generation of oceanographers who worked entirely as “soft money” scientists. “Hard money” meant being in a salaried position at a university or government lab. As soft-money scientists, we depended for our livelihood entirely on government grants or contracts. As one of my lab directors once said, we “lived by our wits.” We acted like small businesses, proposing our ideas to funding agencies (“selling” seems too strong a word), and indirectly to our peers. If successful, we implemented budgets, hired personnel (technicians, administrators), perhaps enlisted students and postdoctoral fellows. Eventually, in completing the research, we produced the product—a scientific contribution, a scholarly work that advanced knowledge of (in my case) the ocean. The Lamont-Doherty Earth Observatory, where I spent most of my career, had about 75 to 100 soft-money researchers at any one time; unlike in many academic departments, these researchers were young, with an average age of 35. Soft-money
x Preface
science was the model for oceanographic research in the second half of the twentieth century. Academic programs were few, while government needs for understanding the ocean were many. One of the admirals in charge of the Office of Naval Research once said, “If it happens in the ocean, we want to know about it.�
PROLOGUE Aboard the Research Vessel Endeavor, South of Iceland, May 1991
W
e looked out through the Endeavor’s windows from the safety of the ship’s main lab, apprehension showing on our faces, knowing we had to go out on deck. The recovery team consisted of my colleague, Chris Langdon; my lab tech, Carol Knudson; Juan Soriano, a tech on loan from an instrument company located in Miami; and me. The seas bordered on chaotic. The wind had kicked up over the day to 55 knots, and the seas responded according to merciless physics. For Chris, Carol, and me, this was another day on the job. Juan, however, was on his first ever oceanographic cruise, and the look on his face showed that a blustery and foul sea was not what he had signed up for. Still, he was game. And regardless, we had a spar buoy harboring plankton samples and irreproducible data to retrieve from those seas. We were already invested in all the work done the previous evening to prepare the experiment. There was no question about recovering the buoy. The Endeavor occupied a station to the south of Iceland, an unforgiving part of the Atlantic in the best of seasons. We, the scientists, were researching relationships among the plankton types in response to the ocean’s daily and weekly whims. My group’s particular job was to measure how much photosynthesis was happening in the resident phytoplankton populations in the ocean’s surface layers. Eighteen hours before, we had collected water samples from various ocean depths, filled special flasks with the water from those depths, spiked them with the radioactive isotope carbon-14, and attached the flasks to a long line according to the depths at which they had been captured. We attached the top of the line to a free-floating 15-foot spar buoy that
2 Prologue
had slack lines along its length that could snag a grappling hook, aiding retrieval. At the top of the buoy we fixed a flashing light. Having everything set, we eased the weighted line over the side, finally casting the buoy overboard to float by itself away from the ship. That was at dawn—at that time of year, about 4:30 AM. The idea was to let the phytoplankton in the samples photosynthesize during the long spring day, taking up the inorganic carbon-14 in the process. Now, just after sunset, we needed the samples back to see how the phytoplankton had done. Endeavor is a midsize (165-foot) research vessel, operated by the University of Rhode Island, and exceptionally seaworthy. Captains of oceanographic ships can handle 55-knot winds, and even much more severe weather. Endeavor’s captain, Tom Tyler, had logged thousands of sea miles. By the time we planned the recovery, it was dark, or as dark as it gets in the month of May at 60 degrees north latitude. We zipped up our work vests and stepped out on deck, balancing with the rolling of the ship. The work vests had long straps that we could clip to a railing along the ship’s outer bulkhead, tethering us to the ship. If we slipped on the deck, we might get bruised, but we weren’t going overboard. We were ready in our persons, and then gaped, open-mouthed, at the seas. A wall of water looked to crash into the ship, and us, broadside. Captain Tyler maneuvered so the wave went under the ship instead of over the railing, but that meant a heavy roll. In the trough of the wave, the captain had our spar, with its light flasher, in sight ahead off the ship’s starboard bow. But we had a problem. The grappling hook and line that we needed to snag the buoy were hopelessly tangled. We were frantically trying to untangle the line, while over our shoulders we saw our buoy just ahead of the midpoint of Endeavor’s starboard side and moving aft. Then we heard screaming from the bridge wing. The captain was ready to retrieve the buoy. We scientists were not. Captain Tyler belted out the most colorful language about our abilities and ancestry, to the effect of “Get that damned hook ready, you . . .” He had a point. He had impressively positioned the ship just right in those 10-foot seas so we could recover the buoy—and we weren’t ready. He’d done his job; we’d failed at ours. Amazingly, he was able to maintain the ship’s position relative to the buoy for a few more precious seconds while we untangled the line, still experiencing the captain’s justifiable fury. Then the toss, and luckily the
Prologue 3
hook grabbed that first time, and held. As the ship rolled toward the buoy and then back away, we could use the roll and the seas to leverage the buoy up to the rail and muscle it aboard, all the while trying to keep our balance against the ship’s lurching with the waves. We pulled aboard the rest of the line with the attached bottles and brought the whole affair inside a bulkhead and out of the weather. Huge sighs of relief. The intrepid oceanographers had another data point in hand—a completed experiment, or at least the hard part. Later that night, the winds increased to 74 knots, technically qualifying this storm as a hurricane, if only briefly. When the readout of the meteorological data on the ship’s computer recorded the wind hitting 74 knots, someone hit the “print screen” button, and we all got a souvenir from the cruise—a badge of honor. While the weather worsened, Carol and I got to work, funneling the seawater from the bottles through small glass-fiber disks, thereby separating out and collecting the particulate matter containing the photosynthesizing phytoplankton. We stored the disks in vials, later to assay their radioactivity back at the lab. For the next 18 hours, the ship was “hove-to” to ride out the storm. No work could be done on deck, no gear put over the side and into the sea. Winds of 55 knots with 10- to 15-foot seas were the worst—or, as I thought at the time, the most exciting—conditions for doing a measurement of the daily photosynthetic production in the ocean. This is not to say that experiments like this never go wrong. Each of my failures in data collection is burned into my memory as a lost opportunity for understanding. In oceanography done from ships, there are no second chances. In the “bench sciences,” if an experiment doesn’t work, you can come back to the lab the next day for a redo. That can’t be done at sea. Each event, each experience, each observation, is unique. Being out on deck that night, exposing ourselves to the storm-tossed seas, was worth the risk. As I discuss in a couple of the later chapters of this book, carbon-14 allowed us to make those measurements from the Endeavor that would otherwise be impossible. Measuring the photosynthetic assimilation of carbon in the ocean, the first step in the ocean’s food web, occupies a small slice of where carbon-14 has been critical to the advance of science. The story of carbon-14 begins about 50 years before our Endeavor cruise,
4 Prologue
and the beginnings of carbon-14’s application in oceanography about 10 years after that, in 1952. The other applications of carbon-14 are as varied as they are groundbreaking and far-reaching. The discovery of carbon-14 in 1940, its application to the dating of artifacts, the working out of carbon dioxide assimilation into organic matter via photosynthesis, giving time scales in oceanography and chronologies to climate—all involve dramatic change in understanding and perspective: revolutions in twentiethcentury science.
HOT CARBON
— ELI KINTISCH, correspondent, Science magazine
JOHN F. MARRA is professor
— JAMES J. MCCARTHY, Alexander Agassiz Professor of Biological Oceanography, Harvard University
“The more times I read this book, the more favorably impressed I am with the clarity and drama of the narrative. Marra’s work will be very well received and appreciated by those interested in how science advances. This is true particularly now, when there is so much controversy surrounding the validity of science per se.” — RICHARD T. BARBER, Harvey W. Smith Professor Emeritus of Biological Oceanography, Duke University
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CA R BON-14 a n d a R EVOLU T ION i n SCI ENCE
of earth and environmental sciences and director of the Aquatic Research and Environmental Assessment Center at Brooklyn College. He was previously a research scientist and associate director of the Division of Biology and Paleoenvironment at Columbia University’s Lamont-Doherty Earth Observatory.
“This is an engaging and witty account of the discovery of carbon-14—there are surprising twists and turns along the way. With its entertaining descriptions of carbon-14’s role in understanding fundamental life processes, dating archaeological specimens, and chronicling past climates, this book is a page-turner for anyone interested in the history of scientific discovery.”
HOT CA R BON
“You may never have heard of carbon-14, but from chemistry to physiology to oceanography, no isotope has affected more aspects of modern life. With precision and verve, oceanographer John F. Marra profiles the most important isotope on earth.”
MARRA
Praise for
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Printed in the U.S.A.
COLUMBIA
J O H N F. M A R R A THERE ARE FEW FIELDS
HOT CA R BON CA R BON-14 a n d a R EVOLU T ION i n SCI ENCE
of science that carbon-14 has not touched. A radioactive isotope of carbon, it stands out for its unusually long half-life. Best known for its application to estimating the age of artifacts—carbon dating—carbon-14 helped reveal new chronologies of human civilization and geological time. Everything containing carbon, the basis of all life, could be placed in time according to the clock of radioactive decay, with research applications ranging from archeology to oceanography to climatology. In Hot Carbon, John F. Marra tells the untold story of this scientific revolution. He weaves together the workings of the many disciplines that employ carbon-14 with gripping tales of the individuals who pioneered its possibilities. He describes the concrete applications of carbon-14 to the study of all the stuff of life on earth, from climate science’s understanding of change over time to his own work on oceanic photosynthesis with microscopic phytoplankton. Marra’s engaging narrative encompasses nuclear testing, the peopling of the Americas, elephant poaching, and the flax plants used for the linen in the Shroud of Turin. Combining colorful narrative prose with accessible explanations of fundamental science, Hot Carbon is a thought-provoking exploration of how the power of carbon-14 informs our relationship to the past.