The long-predicted mobile tsunami has finally landed on U.S. shores. Digital research giant comScore’s March 2015 study “U.S. Digital Future in Focus” provides perspective because of its four-year view.

It reveals that mobile access to the Internet has quadrupled over the past four years, and desktop has risen 37%. (Because tablet Internet access began with almost no share in 2010, it increased by almost 1,800%, mostly because tablet adoption increased exponentially in a short period.) The study also found that the predominant Internet activity on mobile was social networking.

Mobile’s new domination of social media activity did not sap numbers and minutes from desktop digital time, however. Instead, digital time seeped into Americans’ off-hours, as they brought their smartphones and tablets to television time, waiting rooms, Starbucks’ lines and bed. Consumer access grew, allowing for mobile to capture more eyeballs.

The same study found that approximately 31% of all traffic to the top 10 digital properties was mobile-only visitation. For example, Facebook is the number-three digital property, getting 207 million unique U.S. visitors. Google and Yahoo! are numbers one and two.

In fact the authors of the comScore study relate that, “Facebook saw mobile revenues surpass desktop revenues, signaling a shift towards mobile as the primary digital media platform.” Keep in mind that with 31% accessing Facebook through mobile, device usage is not primary yet. The “shift” mentioned by the comScore study authors is “towards” mobile.

Research firm eMarketer explains that U.S. adults have switched their social activity from desktop to mobile. The company predicts that by the end of 2015 more than half of all social networking will occur on smartphones and tablets.