In his famous book Principles of Geology, Being an Attempt to Explain the Former Changes of the Earth's Surface, Charles Lyell stated that Earth's geological features were formed by the same currently observable processes taking place. Charles Darwin was greatly influenced by Lyell's work and proposed that the current diversity of life can also be explained by mechanisms that are in operation today, acting over very long periods of time. Why was this a critical understanding for both scientists?A. They both understood that past processes were different and that only currently observable processes could be tested.
B. They both understood that geological processes and biological processes were different from one another, but were observable.
C. They both understood that although past processes could not be scientifically tested, current processes in both geology and biology could be tested.
D. They both understood that if currently observable processes acted in the same manner in the distant past, those processes could then be scientifically tested

D. They both understood that if currently observable processes acted in the same manner in the distant past, those processes could then be scientifically tested

Explanation:

The scientists observed and analyzed different processes that have occurred. It was discovered that the processes could be linked together and there is the possibility of studying the processes experimental to prove their existence. In addition, they believed that the processes could be tested scientifically.