Final answer:
Charles Darwin's geological discoveries during the Voyage of the Beagle included evidence for an ancient Earth based on fossils in mountainous regions and insights into species adaptation, both critical to his theory of evolution.
Step-by-step explanation:
During the Voyage of the Beagle, Charles Darwin made several crucial observations related to geology. He discovered fossils of sea creatures high in the Andes mountains, which suggested that the earth had undergone significant geological changes over time.
This finding aligned with the principles established by geologist Charles Lyell, particularly the theory of stratification of rock layers indicating an ancient Earth, far older than the 6,000 years as per biblical narratives. Darwin's observations on the Beagle, aided by Lyell's writings on paleontology and a changing Earth, became pivotal in developing his theory of evolution.
Furthermore, Darwin's studies in the Galápagos Islands provided insights into the adaptation and speciation of animals, such as the famous case of the Galápagos finches, which showed variations adapted to different islands and environments. These observations served as compelling evidence for Darwin's later work, On the Origin of Species.