STALACTITES are formed by the drip, drip of water, right? Not entirely. The way caves "breathe" is the true controller, a finding which pours doubt on ancient climate records derived from these structures.

Breath to produce stalactites (Image: Stephen Alvarez/NGS)

Philip Froelich of Florida State University in Tallahassee and colleagues recorded air circulation in the Hollow Ridge cave near Marianna by measuring airborne radon, a naturally occurring radioactive gas. They found that levels were lowest in the winter, when cold, moist air at higher pressure rushes into the cave and flushes out stale, radon-rich air (Earth and Planetary Science Letters, DOI: 10.1016/j.epsl.2009.11.010).

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