What observation did Darwin make that suggested there had been geological changes in Earth's history? A. giant tortoises B. fossils of giant sloths C. fossil shells on top of mountains D. an absence of rabbits in South America

The observation that Darwin made that suggested there had been geological changes in Earth's history were the giant tortoises. The correct option among all the options that are given in the question is the first option or option "A". Darwin was born on 12th of February in the year 1809 and died on 19th of April in the year 1882.