The correct answer is C. Ecology is the study of the relationships between organisms and their environment. It is a branch of biology that deals with the distribution and abundance of organisms, as well as the interactions between them and their environment.
Option A is incorrect because evolution is the process by which species change over time. It is a branch of biology that deals with the history of life on Earth.
Option B is incorrect because ecology is a natural science, not a social science. It does not integrate social sciences to help us understand how the earth works.
Option D is incorrect because ecology does not study the environment in the absence of humans. It studies the interactions between organisms and their environment, including humans.