Question

what is uniformitarianism?
the theory that all rock layers were formed at the same time
the process of determining absolute dates using radiometric dating
the theory that processes at work on earth today are the same as those that worked in earths past
the method of dividing earths history into equal time periods

Explanation:

Uniformitarianism is a geological concept. It posits that the natural laws and processes (such as erosion, sedimentation) that operate in the present day have also operated in the past. This helps in understanding geological formations and Earth's history.

Answer:

The theory that processes at work on Earth today are the same as those that worked in Earth's past.