Here is an example of a tree ring visualisation showing how over time the tree grows and leaves down rings.
I am going to visualise another time series expected lifespan. Gapminder visualises thiswitha line graph. I downloaded the life expectancy data from gapminder.
The interesting points here are the famine where the life expectancy dropped from an estimated 38.3 to 14.1. Also the 1918 flu epidemic causes an obvious drop from 55.3 in 1917 to 49.68 and back to 55.8 in 1919.
The size of each ring should be a good representation on the number of years people could expect to live in that year. However I just multiplied the years given by gapminder *6 to give the number of pixels each circles radius should be.