We are perishable matter yearning for meaning, and time is both the matter and the meaning of our lives. “Time is a river that sweeps me along but I am the river,” Borges wrote in 1940. “Time is the substance I am made of.”

Around the same time, the chemist Willard Libby had a revolutionary insight that brought physics to the poetry of time, measurement to the mystery of this substance we are made of.

Science is stratified, layering discovery upon discovery, continually changing the landscape of knowledge we call reality. The late 1930s and early 1940s were a particularly volcanic time in the life of knowledge. After physicist Lise Meitner prevailed against the odds of her time and place to discover nuclear fission while working with isotopes — nuclear species of the same element that have different numbers of neutrons in their nuclei — physicist Serge Korff theorized that neutrons produced in the upper atmosphere by the newly detected cosmic rays would interact with the abundant isotope nitrogen-14 and become carbon-14 — an unstable isotope of carbon, also known as radiocarbon.

Like all air molecules, radiocarbon makes its way from the atmosphere into living matter — it goes into your lungs with every breath you take, then into your bloodstream, into your digestive system and out of it, into the soil, into whatever grows in the soil, tagging everything along the way with the isotope.

Libby, building on this cascade of discoveries and on his own Manhattan Project work in uranium enrichment, realized that you could measure the amount of radiocarbon in an object and use the isotope’s half-life — the amount of time it takes for radioactive decay to exponentially vanquish the unstable atom, a constant for each element and around 5700 years for radiocarbon — to trace time back and establish the age of the object.

So began what geologists and archeologists would call the “radiocarbon revolution.”

Today, radiocarbon dating has been used to discern the age of the Dead Sea Scrolls and the shroud in which Jesus’s crucified body was swathed, to discover the “wood wide web” of mycorrhizal communication by observing how carbon isotopes are exchanged between root systems, to reveal the biochemical pathways beneath the mysteries of photosynthesis and the metabolic pathways of molecules in the human body, to map disease prevalence and solar activity across time.

But one of the most unexpected and revelatory uses of radiocarbon dating has been to locate an entire civilization in space and in time.

In 1960, months before Libby was awarded the Nobel Prize for his discovery, Norwegian explorer Helge Ingstad and archaeologist Anne Stine Ingstad (who happened to be married to each other) discovered the remains of Norse buildings in Newfoundland — astonishing evidence that the Viking civilization had reached the edge of North America, vindicating the feat of Icelandic sagas that historians had considered mythic hyperbole.

The question became not whether but when it happened.

Excavations went on for eight years. When a few logs of juniper and fir turned up among the archaeological ruins, no one thought much of them.

Meanwhile, radiocarbon labs were being set up around the world — dozens of them by the end of the 1960s, finding unimagined uses for this young science that suddenly banked the river of time. But time takes time — as historian Eleanor Barraclough recounts in her altogether fascinating book Embers of the Hands: Hidden Histories of the Viking Age (public library), it wasn’t until decades after the excavation that researchers realized the Newfoundland wood samples were a once-living record of solar activity. Barraclough writes:

Three of these wood samples bore the marks of a cosmic storm: a spike of the isotope carbon-14 from a solar event that took place in the year 993. They counted forward from the spike in the tree rings to the bark, which gave them the number of years between the cosmic storm and the tree being cut down. This told them that the trees had been cut down in 1021, giving them the only secure year when we know that the Norse categorically had to be present on the edge of North America.

The year the Ingstads completed the Newfoundland excavation, NASA began working on two space probes headed for Mars. They called the program Viking — across time and space, across technologies and civilizations, that same irrepressible human yearning to broaden the known world, to make contact with another.

When Ray Bradbury sat down with Carl Sagan and Arthur C. Clarke for a historic conversation about Mars and the mind of humanity, he captured this elemental impulse:

It’s part of the nature of man to start with romance and build to a reality.

This will always be our romance — to know the unknown, to transcend ourselves, to touch the edges of reality in the finite time we have. Longing may be the only thing in the universe with a half-life of zero.