Chemical paleontology didn't really exist when I was an undergrad, or if it did, it was in its early stges of development and didn't get much attention. Various kinds of chromatography can separate organic molecules left over from dead organisms and preserved in rocks, to give us clues about how those organisms related to each other and to things alive today. Some organic molecules don't last very long, but some are extremely persistent. The New York Times is reporting that amber that appears to have a composition characteristic of flowering plants has been discovered in a coal seam. Said coal seam was deposited 200 million years before flowering plants are thought to have appeared. Abstact from Science here, but the terminology would have meant little to me without reading the news article first.