Americans are becoming less religious, judging by such markers as church attendance, prayer and belief in God, and the trend is more pronounced among young adults, according to a poll released on Tuesday.

The share of U.S. adults who say they believe in God, while still high compared with other advanced industrial countries, slipped to 89 percent in 2014 from 92 percent in 2007, according to the Pew Research Center's Religious Landscape Study.

The proportion of Americans who say they are "absolutely certain" God exists fell even more, to 63 percent in 2014 from 71 percent in 2007.

The percentage of Americans who pray every day, attend religious services regularly and consider religion important in their lives are down by small, but statistically significant measures, the survey found.

The trend is most pronounced among young adults, with only half of those born from 1990 to 1996 absolutely certain of their belief in God, compared to 71 percent of the "silent generation," or those born from 1928 to 1945.

Younger people also are less likely to pray daily, at 39 percent, compared to "silent generation" adults at 67 percent. Young adults are also much less likely to attend religious services, the survey found.

On the other hand, 77 percent of Americans continue to identify with some religious faith, and those who do are just as committed now as they were in 2007, according to the survey. Two-thirds of religiously affiliated adults say they pray every day and that religion is very important to them, the survey found.

The survey also found religious divides among the political parties, with those who are not religiously affiliated more likely to be Democrats, at 28 percent, compared to 14 percent of Republicans.

About 38 percent of Republicans identify as evangelical Protestants - the largest religious group in the party, the survey found. Catholics make up 21 percent of each major political party.

Orianna O'Neill, 21, a student at Beloit College in Wisconsin who comes from a non-religious household but sometimes prays, said she thinks the anti-science, anti-gay rhetoric of some politicians may be turning some young people away from religion.

"The idea of Republicans not believing in global warming is contributing to the notion that religious people are not intelligent," O'Neill said.

Both the 2007 and 2014 studies surveyed more than 35,000 adults and had margins of error of less than 1 percentage point.