Scientists believe nature began to slowly craft Howe Caverns some six million years ago; long before even the ancient, extinct animal known as the woolly mammoth appeared on Earth. Age and beauty are not the only qualities that make our caverns unique. They also happen to be one of a very small number of mineral caves (living limestone cave) in the world. Long ago, the eastern part of New York State was covered by an arm of the Atlantic Ocean. Corals, sponges and many creatures similar to oysters, clams and snails were abundant in these waters. Many of these creatures built their shells from calcium carbonate, which they gathered from their watery home. As this sea life died, their empty shells and fine particles of dirt covered hundreds of feet of the ocean floor. At first, these deposits were very soft. As layers of new deposits fell to the bottom the pressure built up. The lower layers were pressed into a type of rock called limestone. As millions of years passed, the continent of North America rose slowly out of the ocean. This was during the Cretaceous period of Earth's early history some 65-136 million years ago.
Most people think of water as a very "soft" substance: you can plunge your hand into a tub filled with water, and it won't really hurt (On the other hand, if you try the same thing with a tubful of rocks, it will hurt)! But as soft as water seems, its motion and movement - no matter how slow - can have a powerful effect on even very hard rocks over a long period of time.
Because the limestone beds laid down by the sea creatures were softer than many rock formations (such as marble or granite), the rain water trickling down from the ground above soon began to erode the top layers. Small cracks opened up to the layers below, and the rain water dissolved its way through them, too.
In time, the small cracks grew to be large cracks through which underground streams flowed. And that is how the great cave formations and winding passageways of Howe Caverns were formed: over the course of millions of years, underground brooks and streams gently carved them out of the solid limestone deposits left behind by sea creatures eons before.