1 Atmospheric anomaly
Neutrinos produced when high-energy cosmic rays interact with nuclei in the upper atmosphere travel through the Earth almost as if it were not there, which means that there are as many neutrinos passing through you from "below" as there are from "above". However, in 1998 the SuperKamiokande detector in Japan found that the ratio of electron to muon neutrinos coming from opposite sides of the Earth were different, which can be explained if neutrinos change flavour as they pass through the Earth (the circles represent one cycle of this oscillation). This showed for the first time that neutrinos must have mass.