This chart isn't suggesting that more people are clicking on Google ads.
Facebook is a direct competitor with Adwords. Besides, the more time you spend on Google sites, the more of Google's ads you're exposed to. The steepness of Facebook's curve is very likely to freak Google out.
Google and Facebook are competing for ad dollars, but different ad dollars. Google has search advertising pretty much locked. Facebook has figured out brand marketing. Google has been trying to crack that nut for years with AdSense, but Facebook's built-in demographics and time on site looks like they figured it out.
I think commenter's are right. Time on site won't hurt Google's core ad market.
Your comment made me laugh, but in seriousness, FB might be causing people to spend more time than they used to online, so that 200% number is, in a certain sense, not implausible.
Facebook is a direct competitor with Adwords. Besides, the more time you spend on Google sites, the more of Google's ads you're exposed to. The steepness of Facebook's curve is very likely to freak Google out.