Answer: Classified as a theory.
Explanation: The dictionary definition of theory is a system of ideas that are used to logically explain something. It also says that they are also based off of something not entirely connected to the thing the theory is being made about.
Because the idea that the universe has expanded explains such a large number of observations, which in turn leads to more predictions and therefore more observations that support it, this becomes your system of ideas. Because this system was based off of the aforementioned observations in the first paragraph, this proves that it is best classified as a theory.
Observation designed to minimize the effects of variables other than the independent variable.
I believe they cannot start with big trees and bushes because the there is not enough nutrients in the soil, so instead pioneer species pave the way for primary succession.
