WILLIAMSTOWN, Ky. - A 510-foot-long, $100 million Noah's ark attraction built by Christians who say the biblical story really happened has opened in Kentucky.

Since its announcement in 2010, the ark project has rankled opponents who say the attraction will be detrimental to science education and shouldn't have won state tax incentives.

"I believe this is going to be one of the greatest Christian outreaches of this era in history," said Ken Ham, president of Answers in Genesis, the ministry that built the ark.

Ham said the massive ark, based on the tale of a man who got an end-of-the-world warning from God about a massive flood, would stand as proof the stories of the Bible are true.

"People are going to come from all over the world," Ham has predicted.

Ham's group has estimated the ark will draw 2 million visitors in its first year, putting it on par with some of the big-ticket attractions in nearby Cincinnati.

The group says the ark is built based on dimensions in the Bible. Inside are museum-style exhibits: displays of Noah's family along with rows of cages containing animal replicas, including dinosaurs.

The group believes God created everything about 6,000 years ago - man, dinosaur, and everything else - so dinosaurs would've been around at the time of Noah's flood. Scientists say dinosaurs died out about 65 million years before man appeared.

An ark opponent who leads an atheist group called the Tri-State Freethinkers said the religious theme park would be unlike any other in the nation because of its rejection of science.

"Basically, this boat is a church raising scientifically illiterate children and lying to them about science," said Jim Helton, who lives about a half-hour's drive from the ark.

Ham said the total cost of the ark surpassed $100 million, a far cry from a few years ago, when fund-raising for the boat was sluggish and plans for a much larger theme park had to be scaled back.

Millions of people learned about plans for the ark during a debate on evolution between TV's Bill Nye "the Science Guy" and Ham in early 2014.

A few weeks later, a local bond issuance infused tens of millions of dollars into struggling fund-raising efforts. And this year, a federal judge ruled the ark could receive a Kentucky sales tax incentive worth up to $18 million while giving a strict religious test to its employees.

Months later, the tax incentive ruling still has some opponents of the boat scratching their heads.

"It's a clear violation of separation of church and state. What they're doing is utterly ridiculous and anywhere else, I don't think it would be allowed," Helton said.

The court ruled in January that Kentucky officials could not impose requirements on the ark that were not applied to other applicants for the tax incentive, which rebates a portion of the sales tax collected by the ark. That cleared the way for the group to seek only Christians to fill its labor force. New applicants will be required to sign a statement saying they're Christian and "profess Christ as their savior."

Philip Steele, one of the thousands who got an early preview of the ark Tuesday, echoed Ham's oft-repeated comment that the sales tax generated by the ark wouldn't exist if the ark was never built.

"I just don't think they understand it," Steele said of the ark's critics. "They'll be able to keep a portion of [the sales tax] to further their ministry, but so be it."

Asked about the tax incentive, Ham drew loud cheers when he proclaimed no taxpayer money was used to the build the ark.

As much of a boon as the $18 million tax break would be, Nye's agreeing to debate Ham may have helped turn the tide of years of sluggish fund-raising.

Nye, a high-profile science advocate and former TV personality, debated Ham on evolution and drew a huge online audience. Nye later said he didn't realize the attention it would draw and said he was "heartbroken and sickened for the commonwealth of Kentucky."

The video of the debate Answers in Genesis posted on YouTube has 5.4 million views.

About three weeks after the debate, Ham announced that a bond offering from the city of Williamstown had raised $62 million for the project, and a few months later, Answers in Genesis was breaking ground at the site of the ark.