Two different dates have been offered as the approximate end point of the last ice age in North America  The first date was established by testing insect fragments found in samples of sediments to determine when warmth-adapted open-ground beetles replaced cold-adapted arctic beetles  The second date was established by testing pollen grains in those same samples to determine when ice masses yielded to spruce forests
The first date is more than 500 years earlier than the second
Toward the end of the ice age, warmth-adapted open-ground beetles ceased to inhabit areas where the predominant tree cover consisted of spruce forests.