Virginia Froman, age 12, of Tulsa, Oklahoma, for her question:
How old are the Carlsbad Caverns?
When you visit this national park in southeastern New Mexico, time your departure to avoid the millions of bats that flock forth at dusk. Then prepare to be amazed by the breathtaking system of caves. On the walls of the entrance there are paintings done by Indian artists of long ago. The guided tours on two levels include 640 acres of caves, tunnels and stupendous caverns. Everything is sculptured from pale, pastel tinted limestone "icicles" that hang like candelabra from the lofty roofs, graceful pillars and elaborate carvings on walls and ledges.
Carlsbad Caverns, with their artistic stonework, make you think of an enormous underground city, elaborately carved by master stone masons. No, they were not built by those Indian artists who painted pictures on some of the walls or by any other human hands. The immense system of caves was created by slow changes in the earth's crust. The streets, the rooms, the enormous cathedrals are tunneled into an immense bed of limestone that formed under an ancient sea. All the cutting and carving was done by moving water, drip dripping through this porous rock.
Earth scientists think that the massive bed of limestone was formed about 200 million years ago. This was during the Permian Period, when seas swamped this region and most of the western region now occupied by the Rockies. Microscopic water dwellers lived and died there, leaving their chalky shells in thick layers on the sea beds. After about 100 million years or so, the western region of the continent was ready to lift up the lofty Rockies.
As the great mountain system rose, so did the ancient bed of submerged limestone. It became a high and dry plateau at the foot of the Sacramento Range. Streams ran down the eastern slopes to join the Pacos River, cutting its channel southward to join the Rio Grande. Ground water between the streams seeped down and percolated through
the porous limestone. It dissolved the soft, chalky minerals and carried them away. This patient process of carving out the underground caverns is thought to have started about 60 million years ago.
The ground water seeped slowly. It dissolved the soft limestone chemicals and dripped down the walls of the hollows. Much of this water evaporated, leaving its load of chemicals behind. Gradually these deposits formed the elaborate stonework that adorns the ceilings, floors and walls of the underground city.
It is possible that Carlsbad Caverns were carved in this way during the past 60 million years. However, one of its caves has an area of 14 acres and other mammoth chambers may be in the many unexplored regions of the system. Some experts suggest that the carving may have begun ages before, when the limestone was submerged. Perhaps the first hollows were gouged 100 million years ago, by churning waters that began to recede as the massive limestone rose.