Which factor is an indicator that Alberta spent much of its ancient past under a tropical sea?

One key indicator that Alberta spent much of its ancient past under a tropical sea is the presence of marine fossils, such as ammonites and bivalves, found in the sedimentary rock formations of the region. Additionally, the existence of limestone deposits, which typically form in warm, shallow marine environments, further supports this idea. These geological and paleontological clues suggest a long history of marine conditions in what is now Alberta.