Complex sentence: Pérez worked as secretary of the expedition, replacing Manuel Ancízar, who had fallen ill along the trip, his mission was to record events, places, descriptions, statistics, and other valuable information of the places they went to.
Split into simpler sentences: Pérez worked as secretary of the expedition, replacing Manuel Ancízar, who had fallen ill along the trip. His mission was to record events, places, descriptions, statistics, and other valuable information of the places they went to.