Charles Darwin's discoveries on his voyage on the Beagle

Darwin observed that the ancient rivers' silt deposition is the same as it is deposited today. He also studied the geological changes in the Earth's structure convincing him that the mountains took millions of years to form. He also noticed the similarities between the Galapagos finches causing him to believe that they all descended from one common ancestor. He believed that over time the finches adapted to their habitats. Darwin observed many kinds of tortoises in the Galapagos islands and saw that they were similar but the main differences were in neck length and shell differences. He believed that the turtles also descended from a common ancestor. Darwin also discovered the likenesses between the mockingbirds on the Galapagos islands.