"How do I explain the creation of the earth to him in a way that will make sense to him without god complete with scientific backing?"
You may not be able to do this, since he seems unwilling to accept that he might be wrong about the existence of deity. That's the logical stopping point of any conversation on the subject -- if the other person refuses to acknowledge s/he may be mistaken, s/he's completely closeminded and it's pointless to continue. So, first, I would ask that. "Can you acknowledge you might be wrong about this?" If the answer is no, just end the conversation, "Then we have basis to even discuss it."
If the answer is yes, it's important to acknowledge that we don't know *precisely* how the earth formed, but there's a tremendous amount of observation which makes clear to anyone objectively studying it that the earth is billions of years old, its origin was not a supernatural event and a great deal of it can be reasonably explained based on those observations. Since I expect the origin and development of life is involved here as well, this may be a good place for you to start: http://nap.edu/read/6024
"He says it takes more faith to be an athiest or secular humanist then it does to believe in god."
He's wrong, very likely because he doesn't understand what those terms actually mean, and I suspect what he's really saying is that it's *easier* for *him* to believe in deity than to consider he may be mistaken about it.
Hope this helps!