Tanya Smith reads teeth the way most people read books.

Rich details of life—from diet to disease—are etched into each of their layers. And Smith, a biological anthropologist at Griffith University in Australia, has spent more than a decade and a half poring over their chemistry and physical structure. But one detail of these stories has long been lacking: the environmental conditions in which the changes took place.

“People in human origins research have long speculated that climate change and periods of climate instability may have been key drivers in evolutionary steps during the human journey,” Smith says. But the markers used to tease out past climate—things like ice cores and pollen records—don’t give information on tight enough time spans to