When a researcher picks up an object — whether it’s a scrap of leather from a dig site, a fossil from a museum drawer or a newly fallen meteorite — their first question might be, “What is this thing?” A natural follow-up: “How old is it?” The first question is fundamental, no doubt. But the second is powerful, too. It helps place the object in its proper archaeological, geologic or cosmological context. “Without knowing the ages of things, there is no narrative,” says Rick Potts, a paleoanthropologist at the Smithsonian’s National Museum of Natural History in Washington, D.C.
Up until a century or so ago, researchers studying rocks and the fossils they contain could answer the age question only vaguely if at all. Using guidelines established by geologists in the 1600s, they could gauge a rock’s age only in relative terms: For example, Sample A was considered older than Sample B if it came from a lower and presumed older layer of sediment or rock. But Earth is a dynamic place. Missing layers, as well as disturbances from earthquakes, landslides or other upheavals, meant even relative ages for rocks could be difficult to determine. Ditto for the bones, tools and other artifacts within the earth: Previous excavations, or even the day-to-day activities of a site’s ancient residents, could churn the soil and thus disrupt the layers.
Up until a century or so ago, researchers studying rocks and the fossils they contain could answer the age question only vaguely if at all. Using guidelines established by geologists in the 1600s, they could gauge a rock’s age only in relative terms: For example, Sample A was considered older than Sample B if it came from a lower and presumed older layer of sediment or rock. But Earth is a dynamic place. Missing layers, as well as disturbances from earthquakes, landslides or other upheavals, meant even relative ages for rocks could be difficult to determine. Ditto for the bones, tools and other artifacts within the earth: Previous excavations, or even the day-to-day activities of a site’s ancient residents, could churn the soil and thus disrupt the layers.
