The Pew Research Center's latest report on America's religious landscape highlights the significant demographic challenges that Christianity is facing in the U.S.

According to the report, "the percentage of adults who describe themselves as Christians has dropped by nearly eight percentage points in just seven years, from 78.4 percent in an equally massive Pew Research survey in 2007 to 70.6 percent in 2014." Based on the error bars in the survey methods, the number of Christians in the United States is thought to have declined in absolute terms between 2.8 million and 7.8 million during the past seven years.

Over this timeframe, the percentage of unaffilitated increased from 16.1 percent to 22.8 percent -- with the highest rates of growth among younger people. Almost 40 percent of young Millennials (those between the ages of 18 and 24) are unaffiliated. Similar levels (34 percent) of unaffiliation exist among older Millennials (ages 25 to 33). "In the West[ern region of the U.S.], the religiously unaffiliated are more numerous than Catholics (23 percent), evangelicals (22 percent) and every other religious group," the report said.

The highest rates of Christian affiliation exist within the Silent Generation (85 percent; born 1928-1945), followed by the Baby Boomers (78 percent; born 1946-1964), Generation X (70 percent; born 1965-1980), Older Millenials (57 percent; born 1981-1989), and finally the Younger Millenials (56 percent; born 1990-1996).

Between 2007 and 2014, the share of atheists increased from 1.6 to 3.1 percent, and agnostics increased from 2.4 to 4.0 percent. By comparison, the Mormon population is only at 1.6%.

A number of long-term surveys all point to the early 1990s as the start of the rapid growth phase for the unaffiliated. Prior to that point, the unaffiliated population had been approximately constant at 7 to 8 percent since the mid-1970s.