By Lindsey Bever
The year before we age into a new decade — at 29, 39, 49 and so on — we’re more likely to back up and take a hard look at our lives. Year nine, that time leading up to a new chapter, can prompt us to take action, making us more likely to run a marathon, cheat on our partners or even take our own lives, according to research published this week in Proceedings of the National Academy of Sciences.