For years, Timothy Bromage wondered if it would be possible to collect metabolism-related molecules from fossils and study them for clues about how animals lived millions of years ago. It would be a process that he describes as similar to when your doctor analyzes a sample of your blood to gain key insights about your health.

When paleontologists learned that collagen (protein that provides structure to bones, skin, and connective tissue) is preserved in bones, Bromage suspected that metabolites (the molecules produced and used in digestion and other chemical processes in the body) might be hidden there too. He led a team of international researchers in using mass spectrometry to test the hunch by extracting and analyzing the metabolites from fossils.

They ended up being able to determine what animals ate, how they responded to diseases, and what vegetation grew where they lived with surprising precision. In a 1.8-million-year-old ground squirrel, for example, researchers found chemical evidence of a parasitic infection similar to modern-day sleeping sickness. By identifying specific plant molecules—such as aloe and asparagus—in fossils found in a given region, they could determine exactly what the environment was like there millions of years ago. The new method lets scientists describe ancient ecosystems with the precision of modern ecologists, offering new insights about climate change.

Read more about the study in Nature.