Complex sentence: The themes of nature in his work can be traced back to his study of geology as well as the expeditions he took in his early days, first to Greenland in the 1950s and then to Central America, the Arctic, and Greenland in the 1970s.
Split into simpler sentences: The themes of nature in his work can be traced back to his study of geology as well as the expeditions he took in his early days. First to Greenland in the 1950s and then to Central America, the Arctic, and Greenland in the 1970s.