“because that which is known about God is evident within them; for God made it evident to them” (Romans 1:19).
Despite the claims of atheist, there is something intuitive within humanity regarding the notion of God; that there is something, or someone, over us that transcends the natural world. Perhaps this is the very thing to which the wisdom writer is alluding, that God has set eternity in our heart (Ecc. 3:11). From personal experience, at my lowest point in college, and a year prior to my coming to Christ, I had decided to become an atheist. I was a failure at atheism, however, because all I thought about was God. The evidence for God is in, both, plain sight and within (Job 12:7-9; Ps. 19:1). The real issue is never one of knowledge, but acknowledgement.