This chart from The Economist is worth staring at for a while:
The vertical axis is the percentage of total economic output or person-years lived over the past two millennia. According to the chart makers:
By this reckoning, over 28% of all the history made since the birth of Christ was made in the 20th century. Measured in years lived, the present century, which is only ten years old, is already “longer” than the whole of the 17th century. This century has made an even bigger contribution to economic history. Over 23% of all the goods and services made since 1AD were produced from 2001 to 2010, according to an updated version of Angus Maddison’s figures.
In other words, in terms of years lived, one third of post-1AD human history has occurred since 1900, and more than three quarters of total economic output. What accounts for this phenomenon? Matt Ridley’s latest book, The Rational Optimist, provides a great explanation. (Hat tip to Mark Perry)