May 7, 2007 -- "Proving the existence of God is actually a lot easier than you think," said former child star Kirk Cameron, minutes before taking the stage for the "Nightline Face-Off."

It was a warm Saturday night in New York City as a mixed crowd of atheists and Christians converged on Calvary Baptist Church in midtown Manhattan for the first "Nightline Face-Off." And it wasn't long before temperatures began to rise inside the auditorium.

The question for our debate was "Does God Exist?" and both sides went at the issue with a series of passionate declarations and critical attacks on the arguments of their opponents. It was a clean but unflinching contest.

Former child star Kirk Cameron and his evangelist colleague Ray Comfort had pledged to prove the existence of God, scientifically. Cameron and Comfort run an organization called the Way of the Master, which comprises a Web site and cable television show, all focused on preaching what they say is the truth of Christianity.

Cameron opened the debate by addressing the crowd:

Hi, I'm Kirk Cameron and my partner and I Ray Comfort come to you tonight not as molecular biologists or rocket scientists, but simply as an author and an actor, and we want to do two things that fly in the face of convention. One, we'd like to show you that the existence of God can be proven, 100 percent, absolutely, without the use of faith. And secondly, as a former atheist myself -- an evolutionist -- I want to pull back the curtain and show that the number one reason that people don't believe in God is not a lack in evidence, but because of a theory that many scientists today believe to be a fairytale for grownups.

They were confronted by the might of the "rational response squad" — in the form of unabashed atheists Brian Sapient and his comrade, a woman who goes by the name of Kelly. They had been included in a previous "Nightline" report, telling the story of the Blasphemy Challenge in which they invited atheists to deny the existence of the Holy Spirit by posting videotaped denunciations on their Web site.

Comfort saw the piece on the Blasphemy Challenge, and he immediately e-mailed "Nightline," saying, "We would like to challenge them to a public debate. … Let's hear their best evidence as to why God doesn't exist, and let the audience decide whose evidence is based on faith and whose is based on fact. We cannot only prove that God exists, but we can prove that the atheist doesn't."

Sapient had this to say when he addressed the crowd at the debate:

"I want to start off by thanking ABC, Kirk and Ray and the audience for their ears and their participation of the discussion of this magnitude. The Rational Response Squad was formed to respond to irrational claims, and the most wildly held irrational claim are the ones offered by religion. Ray and Kirk have agreed to offer scientific proof that god exists without invoking faith of the Bible, and we are here to respond to those claims.

For more than 90 minutes, they battled over the main arguments of evolution, historical evidence and the existence of God. The audience, which was divided between Christians and atheists, asked penetrating questions, and there were also a number of contributions submitted by viewers at ABCNEWS.com.

It was a no-holds-barred debate that was well worth watching.