We see that we have a fairly even distribution of points until the 1940s, a large burst of points in the 1950s-1960s, and two points in the 1980s.
there are many time periods before the 1940s (which may be caused by noisiness of the data in the first half of the century), a big transition between time periods in the 1950s-1960s, and a transition between time periods in the 1980s.