The graph is from a paper by
Labor force participation rates of married women rose markedly over the 20th century, from 4.4% in 1900 to 59.1% by 2000; see Figure 1. Participation by single women also rose, but not as dramatically, from 44.5% to 66.7%. In contrast, participation rates of men, whether married or single, have fallen modestly over the same time period.The authors claim
We find that the increase in the relative wage of women is the most important explanation of the increase in married womens’ market work time over the twentieth century. Changes in fertility had large effects up to 1980, but little effect thereafter.
The finding is not new, and when several papers reach similar conclusions we can be more certain of the "real" trends.