The magnificent speleothems (cave formations) that continue to grow and decorate Carlsbad Cavern are due to rain and snowmelt soaking through limestone rock, then eventually dripping into a cave below and evaporating. Those water drops have absorbed gasses and dissolved minerals from the soil and limestone above. Wherever that water drop evaporates and releases carbon dioxide in an air-filled cave, a small amount of mineral-mostly calcite, is left behind. Thus, drip-by-drip, over the past million years or so, Carlsbad Cavern has slowly been decorating itself.