Now if we take what Karl Popper said, that scientific knowledge is the search for "truth" not the search for "certainty", then what about the theory of evolution is objectively truth? Certain aspects of it are scientific, are areas where predictions can be made, can be falsifiable, such as the behavior of bacteria, the behavior of cells, etc, but not completely.
So we can say the behavior of cellular life is an area of life sciences. This knowledge could have been acquired without the full theory of evolution. The behavior of bacteria is predicted by the theory of evolution, so we can say that is a legit prediction, but the topic of "origin of life" isn't science, can't make predictions and is just speculation. If we removed all the "origin of life" parts from the theory of evolution then some parts of it are scientific and useful. Origin of life is entirely speculative and educated guessing, and primordial soup after 80 years now researchers are saying it's no longer the best guess.
There have been tests to try to recreate primordial soup which have all failed as far as I know. And just like with the big bang we don't have the ability to use science to explain certain things.
Many scientists and philosophers of science have described evolution as fact and theory, a phrase which was used as the title of an article by paleontologist Stephen Jay Gould in 1981. He describes fact in science as meaning data, not absolute certainty but "confirmed to such a degree that it would be perverse to withhold provisional assent". A scientific theory is a well-substantiated explanation of such facts. The facts of evolution come from observational evidence of current processes, from imperfections in organisms recording historical common descent, and from transitions in the fossil record. Theories of evolution provide a provisional explanation for these facts.[1]
So the facts generated by science are the facts (behavior of bacteria, etc). The theory of evolution exists to try to explain the science in a coherent way. In my opinion the theory of evolution has gaps, holes, and in some cases best guesses like the origin of life, which take it away from being scientific. In a sense it tries to explain stuff which can't be tested as well as some stuff which can be, so while the behavior of bacteria can be tested the origin of life is a speculation (like the origin of the universe).
References
University of Kansas. (2017, September 13). Evolution of 'true frogs' defies long-held expectations of science. ScienceDaily. Retrieved September 18, 2017 from www.sciencedaily.com/releases/2017/09/170913193106.htm
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