This article originally appeared on Undark.
The first and only time Steve Jackson spoke to Bill Critchfield was in the late 1980s. Critchfield, an authority on the conifers of North America, was at home recovering from a heart attack. Jackson, then a postdoctoral researcher at Brown University, had called looking for advice on how to tell jack pine from Virginia pine.
Jackson was also curious about something the elder botanist had mentioned in a recent paper: mysterious spruce fossils from the American Southeast. The fossils dated to the end of the Pleistocene ice age, about 18,000 years ago, and had been found across the region, including in Louisiana's Tunica Hills. Scientists had usually identified the fossils as white spruce, a species that now lives far to the north, but they'd been arguing for decades about what its presence said about the region's ice age climate. Some held that white spruce pointed to a climate similar to modern Canada or Alaska. Others argued that the climate had been milder than that, and suggested that the spruce fossils had been carried south from somewhere else.