Identify the key requirement for an explanation of a natural phenomenon to become a theory

In order for a natural phenomenon to become a theory, it should follow the steps in scientific method.

First it will start as hypothesis, suggesting solution for an unexplained occurrence that seems not to fit in any accepted scientific theory, it means it should have not been proven yet.

Any theory should be based on careful and rational examination of facts. Usually, a scientific theory, in accordance to scientific method should be tested repeatedly using some observations and predefined protocol of experiments. Scientific theory also includes scientists’ explanations and interpretations of facts which can be observed and measured.  Scientific theories however are testable.