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

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.

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 …