Complex sentence: The principal artesian aquifer is the largest, oldest, and deepest aquifer in the southeastern U.S. Ranging over, it underlies all of Florida and The Floridan portion developed millions of years ago during the late Paleocene to early Miocene periods, when Florida was underwater.
Split into simpler sentences: The principal artesian aquifer is the largest, oldest, and deepest aquifer in the southeastern U.S. Ranging over, it underlies all of Florida. The aquifer developed millions of years ago during the late Paleocene to early Miocene periods, when Florida was underwater.