“In work published in Science magazine in 2011, Mr. Michel and the research team tapped the Google Books data to find how quickly the past fades from books. For instance, references to “1880,” which peaked in that year, fell to half by 1912, a lag of 32 years. By contrast, “1973” declined to half its peak by 1983, only 10 years later. “We are forgetting our past faster with each passing year,” the authors wrote.”
via Literary History, Seen Through Big Data’s Lens - NYTimes.com