No abstract

Current genetic and archeological evidence allows for inland, coastal, or multiple pathways to peopling of the Americas.

Significance A key element underpinning the controversial hypothesis of a widely destructive extraterrestrial impact at the onset of the Younger Dryas is the claim that 29 sites across four continents yield impact indicators all dated to 12,800 ± 150 years ago. This claim can be rejected: only three of those sites are dated to this window of time. At the remainder, the supposed impact markers are undated or significantly older or younger than 12,800 years ago. Either there were many more impacts than supposed, including one as recently as 5 centuries ago, or, far more likely, these are not extraterrestrial impact markers.

No abstract

A laboratory investigation was made of the effects of textural and structural stratification within the profile on rate of water infiltration into soil. A recording infiltrometer was devised and a method developed for obtaining uniformly packed tubes of soil. Infiltration data were obtained for soil conditioner treated Palouse silt loam. These data were used to test several infiltration equations found in the literature. It was observed that none of the equations tested adequately describe the experimental data. Effects of strata within soil were related to the pore characteristic differences between the layering material and the surrounding soil. When most of the pores in a layer were larger than those in the surrounding soil, infiltration was temporarily inhibited after the wetting front reached the layer. The degree of inhibition was increased when the pore sizes in the layer were increased. Water must accumulate at a layer‐soil interface until it is at a tension low enough to allow it to move into pores in the layer. Water movement into the surface is reduced while the accumulation takes place.