英语听力：冰河绿洲—16

This triggered other dramatic changes. As sea levels dropped, so did the inland water tables. Florida's fresh water drained away through the porous limestone rock. Pools dried up and springs diminished. Florida was on the brink of drought. And animals would have had to travel to find food and water. So each year, mastodons would have migrated to the wetter regions.

But in a few key places, water was still pushed up from underground as a spring, a vital oasiswhere wildlife would have converged from many miles around. Many animals would have fed on the surrounding vegetation and others come here to drink. And predators would have laid anambush for the unwary. It's no wonder that so many fossil bones have been found on the bottom of these springs, clues that can open up a window on the ice age past.

Bringing this evidence together, we can create a living picture of this region as it was then. We can now go back 13,000 years and see what a day around one of Florida's springs might have been like.

Dawn on the southeast tip of ice age North America. On the banks of a spring-fed pool, the early grazers stir.