Analyzing traces of leaf waxes from land plants that over millennia accumulated in deep sea sediments, a team of researchers led by the University of Arizona reconstructed the history of monsoon activity in northern Mexico. Their results, published online on Sept. 3 in the journal Nature Geoscience, help settle a long-standing debate over whether monsoon activity shut down completely under the influence of cooling brought about by the ice sheets that covered much of North America, or was merely suppressed.