With new dating on charcoal from a context stratigraphically above human footprints set in the playa at Alkali Flat in the US, Bennett et al. writing in Science demonstrate the presence of humans in North America between 23-21 ka ago. This is a big deal.
There has been a lot to suggest that humans occupied the Americas much earlier than what was once the establishment “Clovis-first” view. Btw, it was appropriate to be skeptical about earlier occupation. For a long time, no good dates were shown to be older than ~14.5 ka BP. There were equivocal dates from contexts that were clearly human, and some not definitively human. Whether it was a model of initial overland migration via a Bearing land bridge or via the coastal route, the good evidence fit either model. Over the last decade, some good evidence of human activity has emerged of humans ~16 ka in North America, and earlier.
What’s really cool is that this is starting to line up nicely with the paleoclimate record, which is quite excellent (and improving) for the period in question. Climate conditions that would seem necessary to permit humans to transit in large numbers (what is presently) the Bearing Strait are different than what would seem optimum for humans to thrive in the Americas. During the Last Glacial Maximum (LGM) about 22 ka BP, a global cool period had caused ice sheets to accumulate on land, lowering global sea levels by ~125 m below present (local sea levels vary based on coastline shape, current, season, etc.). Just prior to the LGM, there was a sudden (as these things go) warm event (known as Dansgaard-Oeschger 2), probably due to changes in North Atlantic overturning circulation. During D-O events, conditions over the middle of the North American continent became relatively warm and dry, though on average cooler than today. Runoff from ice sheets caused the formation of large Pleistocene lakes where today are salt pans, or playa. The wetland edges of these lakes were rich ecologies with abundant plant and animal life — including, apparently, humans.
Mastodon image source.