The cave began forming about a million to a million and a half years ago, in a manner similar to many caves. A large crack in the surface of the rock, called the cave's "lifeline", allowed rain water to seep into the stone. In the air, rain combines with carbon dioxide to form a weak carbonic acid. Though this acid is not very strong, it is strong enough to dissolve away the limestone after it seeps in through the "lifeline". Over time, large cavities were dissolved in the stone and as the water table dropped, the water drained out and the cavities filled with air. Now that the cavities are filled with air instead of water, the water droplets coming from the "lifeline", which are saturated with dissolved calcium carbonate, deposit solid calcium carbonate, which builds up over time to create speleothems. This is a very gradual process, usually taking 50 to 150 years to form one cubic inch of material, and continues to this day.