In October, 2010, an Italian religious historian named Alberto Melloni stood over a small cherrywood box in the reading room of the Laurentian Library, in Florence. The box was old and slightly scuffed, and inked in places with words in Latin. It had been stored for several centuries inside one of the library’s distinctive sloping reading desks, which were designed by Michelangelo. Melloni slid the lid off the box. Inside was a yellow silk scarf, and wrapped in the scarf was a thirteenth-century Bible, no larger than the palm of his hand, which was falling to pieces.

The Bible was “a very poor one,” Melloni told me recently. “Very dark. Very nothing.” But it had a singular history. In 1685, a Jesuit priest who had travelled to China gave the Bible to the Medici family, suggesting that it had belonged to Marco Polo, the medieval explorer who reached the court of Kublai Khan around 1275. Although the story was unlikely, the book had almost certainly been carried by an early missionary to China and spent several centuries there, being handled by scholars and mandarins—making it a remarkable object in the history of Christianity in Asia.

Melloni is the director of the John XXIII Foundation for Religious Sciences, an institute in Bologna dedicated to the history of the Church. He had heard of the Marco Polo Bible, but he was unaware of its poor condition until a colleague spotted the crumbling book at an exhibition at the library, in 2008, and pitched a project to restore it and find out more about its past. “It was like a sort of Cinderella among the beautiful sisters,” Melloni said. Like other people accustomed to handling old texts or precious historical objects, Melloni has a special regard for what Walter Benjamin called their aura: “a strange weave of space and time” that allows for an intimation of the world in which they were made. “You have in your hand the manuscript,” Melloni said. “But also the stories that the manuscript is carrying.”

The restoration took eighteen months. Ten thousand pieces of the Bible were reassembled. In the process, Melloni was determined to subject the document to the latest scientific analysis. “We should do on this Bible the type of thing that would be done on the ‘Mona Lisa,’ ” Melloni told his colleagues. He contacted the cultural-heritage center at the Polytechnic University of Milan, the largest scientific school in Italy, to ask advice. In addition to standard conservation tools, like ultraviolet photography and infrared spectroscopy, which is used to study pigments, the experts there suggested proteomics. “It was the first time I heard the word ‘proteomic’ in my life,” Melloni recalled.

Proteomics is the study of the interaction of proteins in living things. Where genomics studies humans’ roughly twenty thousand genes, proteomics is concerned with the shifting array of proteins assembled by those genes—our biological content, more or less, from albumin, which makes up sixty per cent of our blood proteins, to beta-amyloid, a family of brain molecules that can be a potential sign of Alzheimer’s disease. Proteomics aims for completeness. The proteome of a single human cell, which might contain billions of proteins, is sometimes compared to an atlas. It can guide geneticists or drug companies to early markers of a disease, or to the precise mechanism of aging, or to promising targets for cancer treatment. The field has been made possible by spectacular advances in data analysis and in lab instruments, which become cheaper and more powerful each year. Top-of-the-line mass spectrometers now allow chemists to sort through thousands of types of proteins in a sample, and to study them, one molecule at a time.

Since 2000, proteomics has attracted the attention of a small clutch of scientists who believe that it has the potential to immensely expand our knowledge of the past. Under the right conditions, proteins can survive for millions of years. In recent years, proteomic studies of art works and archeological remains have yielded biological information of startling clarity, revealing gossamer-thin layers of fish glue on seventeenth-century religious sculptures and identifying children’s milk teeth from pits of previously unrecognizable Neolithic bones. In 2008, researchers were able to sequence the proteins of a harbor seal that remained on the surface of six-hundred-year-old cooking pots found at an Inuit site in northern Alaska. Three years later, chemists found a hundred and twenty-six different proteins in a mammoth femur. With new proteomic techniques emerging constantly, the field has a heady, chaotic atmosphere of possibility. At a four-day conference called Ancient Proteins, held this summer in Copenhagen, presentations had titles such as “Biologics in Art: Whaaat???,” “Palaeoproteomic Analysis of Binding Media and Adhesives in Ancient Egypt,” and “Through the Looking Glass, and What Amino Acids Found There.”

Melloni arranged to have some fragments of the Bible sent to Milan. In the fall of 2011, a few pieces arrived at the laboratory of Pier Giorgio Righetti, a tall, slender chemist in his seventies, with a neat beard, like Trotsky’s. Righetti is known in the world of proteomics for his work on electrophoresis, a process that helps to sort molecules by size and by electrical charge. He comes across as a happy man, prone to finishing his sentences with a long, high-pitched laugh. Once, when we were riding the subway together in Milan, we walked onto a platform just as the train was coming in. “Yes, yes, yes! We are lucky! We are lucky!” he yelled as he ran up to the doors, as if this were the best thing to happen to him in years.

Righetti started out studying the proteins of maize, in 1971. Back then, a laboratory might spend years sequencing a single protein. “Now proteomics is like when you are looking at a starry sky,” Righetti said. Unlike the genome, which stays largely the same, an organism’s proteome changes all the time. Our cells produce different proteins when we are asleep, when we are afraid, and when we are sick. Proteins from the past are the biological remnants of a specific instant: a supper of seal, an ailing mammoth. “It is frozen,” Righetti said. “A certain moment in the life of this fellow.”

Testing the Marco Polo Bible was the first time that Righetti had studied something old. He has an affinity, however, for subjects that are historical and romantic. His father was an elementary-school teacher and a poet. As a boy, Righetti dreamed of studying literature, but was afraid of being poor. Alongside his chemical research, he has written two novels and is currently at work on a third, a story about the Palestinians since Biblical times. His scientific papers often have literary titles that belie their abstruse content. (A 2007 paper called “Sherlock Holmes and the Proteome” was about hexapeptide ligand libraries.) For the study of the Bible, Righetti read at least six books about Marco Polo.

In the lab, he struggled with the manuscript pieces. They were badly withered and resistant to the normal technique for removing proteins, which is done with a solvent. One evening, in desperation, a colleague of Righetti’s warmed one of the fragments in a microwave. “A bloody microwave!” Righetti said. It worked.