In 1909 the Model T was already in mass production. I think that represents a huge shift in day-to-day life that happened between 1900 and 1950 but not 1909 and 1959.
On the other end of the timeline, I think Google going from a $25 million funding round in 1999 to a $100+ billion market cap in 2009 represents major changes in how society works.
