Deadly Voyager: Hemisphere-wide inferno from a comet strike only 13kya

For some reason, back in 2010 bunches of geologists really hated this idea and desperately tried to suppress it, going so far as to--apparently!--deliberately fail to replicate findings, and then report that as if the original findings had been fabricated.

The latter have since been replicated by dozens of researchers. Throughout the Western hemisphere, a thin layer exactly the same age everywhere is black with charcoal and laced with platinum-enriched melted particles and nanodiamonds.