First attempts in Europe and North America
The understanding of the nature of floral change across the K–T boundary has been delayed both by the nature of the plant fossil record and by poor temporal resolution in Cretaceous nonmarine rocks. The rapid rise of angiosperms in the Early Cretaceous and the rarity of thick, continuously fossiliferous, Cretaceous sections further complicated this situation. Angiosperms dominate modern vegetation and account for more than 80% of living species, but they appeared abruptly in the fossil record over a span of 25 million years in the Early Cretaceous. Early Cretaceous angiosperm leaves are superficially similar to living ones, and this similarity gave rise to the misconception that extant angiosperm genera first appeared in the Early Cretaceous. This sudden appearance, known as Darwin's abominable mystery, set the stage for several misconceptions and stratigraphic problems. Moreover, paleobotany has traditionally been summarized at the stage level and no great stock has been placed in obtaining the precise age of fossil floras. Before the Alvarez challenge, it was considered sufficient to state that a flora was Cenomanian or Campanian, or perhaps late Cenomanian or early Campanian. These stages are 6.1 and 12.9 million years in duration, respectively, and clearly represent too long of a time bin to be relevant to resolving change over short periods of time.