Geologic archives show that the Earth was dustier during the last glacial period. One model suggests that increased gustiness (stronger, more frequent winds) enhanced dustiness. We tested this at Loveland, Iowa, one of the thickest deposits of last-glacial-age (Peoria) loess in the world. Based on K/Rb and Ba/Rb, loess was derived not only from glaciogenic sources of the Missouri River, but also distal loess from non-glacial sources in Nebraska. Optically stimulated luminescence (OSL) ages provide the first detailed chronology of Peoria Loess at Loveland. Deposition began after ~ 27 ka and continued until ~ 17 ka. OSL ages also indicate that mass accumulation rates (MARs) of loess were not constant. MARs were highest and grain size was coarsest during the time of middle Peoria Loess accretion, ~ 23 ka, when ~ 10 m of loess accumulated in no more than ~ 2000 yr and possibly much less. The timing of coarsest grain size and highest MAR, indicating strongest winds, coincides with a summer-insolation minimum at high latitudes in North America and the maximum southward extent of the Laurentide ice sheet. These observations suggest that increased dustiness during the last glacial period was driven largely by enhanced gustiness, forced by a steepened meridional temperature gradient.

The α, β, γ, and δ polymorphs of Y2Si2O7 were synthesized using sol-gel and solid-state methods. The structures of the α and γ polymorphs were determined by identification of isostructural rare-earth disilicates, and the structures were refined using Rietveld analysis of X-ray powder diffraction data. The α polymorph crystallizes in space group P1, with a=6.5872(6) Å, b=6.6387(7) Å, c=12.032(1) Å, α=94.501(7)°, β=90.984(8)°, γ=91.771(7)°, and volume=524.16(9) Å3. The γ form is described by space group P21/c, a=4.68824(5) Å, b=10.84072(9) Å, c=5.58219(6) Å, and γ=96.0325(3)°. The anisotropic thermal expansion of each phase was measured using high temperature diffraction up to 1200 or 1400 °C, depending on the stability of the polymorph. The thermal expansion is highly anisotropic for all polymorphs, with the low-expansion direction normal to the long axis of the corner-shared SiO4 tetrahedra.

Our study of caudatum sorghums in Africa and the ethnography, history, and archaeology of regions where caudatum sorghums are grown has led us to the following conclusions.

The distributions of caudatum sorghums and Chari-Nile-speaking peoples coincide so closely that a causal relationship seems probable.

Caudatum sorghums appear to be a product of selection by Chari-Nile-speaking peoples for a hardy crop which will produce a large amount of grain under adverse conditions with a minimum amount of care. Caudatums can produce grain in spite of either droughts or heavy rains during the growing season and can produce grain in places where no other indigenous African crop can grow.

Caudatum may be a relatively new race of sorghum. Available evidence indicates it was developed some time after about 350 A.D. and before about 900 A.D., the date for caudatum found at Daima mound, south of Lake Chad.

By about 1000 A.D. caudatum was probably being grown in many parts of the savanna belt stretching from the eastern shores of Lake Chad to southwestern Ethiopia. This is assuming that the evidence of caudatum culture at Daima is indicative of a general phenomenon occurring in a region with close intercultural contacts.

The large number of varieties of caudatum in the Republic of the Sudan suggests that caudatum sorghums have been grown in the Sudan for a relatively long time and may have been developed there.

A caudatum and cattle-based economy has probably been an important factor in making possible the present level of occupation of regions now inhabited by Chari-Nile-speaking peoples.

On the basis of oral histories and archaeological remains of people in northern East Africa, we have concluded that caudatum-based agriculture was probably introduced to Uganda and Kenya no later than the period from 1500–1800 A.D., when the Luo occupied the areas in which they live at the present. However, it is not unlikely that caudatums were introduced more than once as various Chari-Nile-speaking groups made their way into East Africa.