Have you ever been in a cave? If you have, perhaps someone has told you that the rock formations hanging from the ceiling—called stalactites—are thousands or even tens of thousands of years old. Scientists tell us that stalactites take 100 years, on average, to grow one inch. But just how accurate is this figure?
Stalactites grow where water seeps through limestone rock, dissolving limestone in the process. When this water containing dissolved limestone emerges from the roof of a cave, it hangs for a moment. In a current of air, some of it evaporates, causing the limestone to deposit. Finally, the remaining water drops to the floor of the cave and continues to evaporate and deposit. The deposit on the floor is called a stalagmite.