The history of the Standard Model is older than a century! The first particle to be discovered was the electron, back in 1897, by Joseph John Thomson at the Cavendish Laboratory in Cambridge. At that time, not only the Standard Model but even Quantum Mechanics, the physical theory at the basis of it, had not been formulated yet. The Higgs boson is the last particle that was discovered in 2012 at the LHC, CERN.
Not everyone in the scientific community is convinced of the existence of Dark Matter. An active research field is the so-called MOdified Newtonian Dynamics (MOND). The main idea is that the laws describing gravity must be modified in such a way that they can explain astrophysical observations without the need for additional matter. While this option is not completely ruled out, it seems harder and harder for these theories to explain the current evidence.
The original equations of General Relativity, describing the interaction between matter and gravity, predicted an expanding Universe. Einstein was not satisfied with this result and included a constant term in the equations, the so-called Cosmological Constant, in such a way that the solution allowed for a static Universe. However, soon after the development of his theory, astrophysical observations showed that the Universe is expanding! Einstein defined the Cosmological Constant as the greatest blunder of his career. However, in 1998, two groups of astrophysicists showed that the expansion of the Universe is accelerating, and this can be explained by reintroducing the Cosmological Constant. This term is interpreted today as a parametrization of Dark Energy.