The image shows a portion of the fossil record that spans several million years. In the image, the numbers designate different rock layers, with the number 1 corresponding to the oldest rock layer.

What statement provides the best explanation for the change in the species between rock layer 1 and rock layer 2?
A. An abrupt change in the environment caused the original species to evolve into several new species.
B. The original species hybridized with a single new species, resulting in a variety of species.
C. Humans introduced several new species into the environment after the original species had died out.
D. The original species died out, and several new species evolved that were better suited to the environment.