Water progressively dissolves the rock between the layers of rock and inside the joints. This resulted in a big, water-filled area. The current river breaks through the rock strata as it flows down the river valley, opening up the cave. This allowed the water to drain and provided us with an air-filled cave. As the water recedes, you can see that the bottom layer of rock is still damp. Caves are often used as shelters by people or animals. Caves with high ceilings provide more space for a shelter than those with low ceilings. Long ago people found comfort and protection from the elements in caves. Also, caves provide ideal places for hiding from predators. Caves also provide valuable resources for humans to use. Humans have used the gas dissolved in water to burn fuel since ancient times. Modern industries also benefit from using natural gases found in water wells. These gases are used to make plastic and other products without burning any solid materials. Finally, caves provide shelter for people who need it, such as refugees or soldiers. The formation of caves is an important part of earth science because they contain information about the history of our planet. Scientists can study the different types of rocks within caves to learn more about how the Earth's surface has changed over time. Caves also contain evidence of past climate changes.