Complex sentence: Cactus Hill is one of the oldest archaeological sites in the Americas, and if inhabited 18,000 to 20,000 years ago, provides evidence supporting the Solutrean hypothesis.
Split into simpler sentences: Cactus Hill is one of the oldest archaeological sites in the Americas. If proved to have been inhabited 18,000 to 20,000 years ago, provides evidence supporting the Solutrean hypothesis.