Snail Species Composition and Ice Age Summer Temperatures

Advancing and retreating glaciers during Ice Ages crushed rock into dust. Meltwater pulses that occurred when climate cycles shifted to warm stages washed this dust into rivers. Then, when climate cycles shifted to arid stages and rivers shrank in size, exposing the sediment, wind blew this dust into huge hills alongside the rivers. This wind-blown dust is known as loess. Hills made from loess are located up and down the Mississippi River Valley, but today they are covered by vegetation that originally took root when climate became more moist and warmer. Land snail shells are often found in the loess. Scientists can use the snail species composition to estimate past average summer temperatures. (Land snails are mostly active during the warmer months.) Every species of snail occurs in ranges within certain temperature parameters. Scientists can also radio-carbon date snail shells. By dating the subfossil snail shells and identifying the species present, scientists can estimate past…