The repeated cycles of ground freezing and thawing that occur in many places don't do a good job of churning the soil, a new study suggests.
Freeze-thaw cycles and the burrowing of animals are among the many natural phenomena that can mix the upper layers of Earth's soil, says James M. Kaste, a geologist at Dartmouth College in Hanover, N.H. To study the relative effectiveness of these mechanisms, he and his colleagues measured beryllium-7 and other radioactive elements that fall to the ground in precipitation and immediately attach themselves to particles at the surface. By documenting the concentrations of these short-lived elements at various depths, the researchers inferred how quickly surface soil mixes downward.
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