An example of a superseded theory is the geocentric universe. According to the information available at the time, the ancient Greeks, among others, believed that earth was the the orbital centre and celestial bodies moved around it. This has obviously been superseded by the now extensive (but not complete) knowledge of the structure of the universe now.
Scientific theories like gravity, Einstein's Theory of Relativity, evolution aren't likely to be superseded or completely discredited in the same way. There is just too much physical evidence supporting them. The theories may be refined, as here:
In the early 20th century, genetics was integrated with Darwin's theory of evolution by natural selection through the discipline of population genetics. The importance of natural selection as a cause of evolution was accepted into other branches of biology. Moreover, previously held notions about evolution, such as orthogenesis and "progress" became obsolete. Scientists continue to study various aspects of evolution by forming and testing hypotheses, constructing scientific theories, using observational data, and performing experiments in both the field and the laboratory. Biologists agree that descent with modification is one of the most reliably established facts in science. Discoveries in evolutionary biology have made a significant impact not just within the traditional branches of biology, but also in other academic disciplines (e.g., anthropology and psychology) and on society at large.
It's only because the science is so grossly inconvenient to those who want to argue that the bible is true that people erroneously say 'but evolution is just a theory.'