The pulse of large mammal extinctions at the close of the last ice age was a pronounced ecological catastrophe in the Western Hemisphere. Available paleoenvironmental, paleontological, and archeological data are largely concordant with the “overkill” hypothesis proposing that human predation was the cause of these extinctions. Climatic explanations fail to postulate specific mechanisms accounting for the event's timing, differential impact, geographic extent, and stratigraphic singularity. Lack of provisional acceptance of the overkill hypothesis, when no viable alternatives exist, may be in part because this unconventional hypothesis violates a strong sociocultural bias, the image of prehistoric man as the “noble savage”.

Pleistocene proboscidean fossils recovered from the Bering Land Bridge strengthen the hypothesis that man may have originally colonized the Americas via this route during times of lowered sea level.

Distinctive patterns of growth rings in increment cores from old-growth Douglas-fir (Pseudotsuga menziesii) stands identify A.D. 1800 as a more precise date for the eruption of tephra layer T by Mount St. Helens, Washington. Layer T was previously inferred to date to about A.D. 1802. Growth patterns also establish A.D. 1480 as the date of eruption of the earlier layer Wn, previously estimated as dating to about A.D. 1500. The timing of radial tree growth places a small limitation on the seasonal resolution of these new tree-ring dates.