to the young earther who said, "but evolution is just a theory"

First, let me apologize for my flippant response. I said, 'you obviously don't know what a scientific theory is.'  While this was clearly true, why would I expect you to be interested enough to learn about how science works?  Other than, of course, offering your opinion in the first place.

Here is what I wish I had said; You are correct.  And you are nearly at a very important distinction between science and myth, science doesn't claim or need to be true.  Science just has to work. 

A central component of your belief system is God is the source of absolute truth.  This truth comes to humans through the written word and the voice of His Prophets, like your Dad in his garage church.  We struggle with the revealed truth because God's Absolute Truth in beyond human comprehension.  Could this be the real reason why fundamentalists have such issues with atheists: we do not accept the authority of the revealed Truth?

Science has no need of absolutes.  An answer that works 95% of the time is good enough (p).  I imagine this is hard for you to think about, there are no absolutes, everything is relative.  I would also like to imagine that you would ask, why?  Why give up the comfort and surety of AT for p?  In the words of my favorite webcomic author because, "science works bitches."  Exploring the world through rational/empirical methods is the only thing that has ever worked to help us learn about the world.  Experience and trial and error have lead to techniques that help us to function, but science shows why things work.  We don't need an Ultimate knowledge, we just need to be able to predict what will happen next.  That's what science does. 

Yes evolution is just a theory - so is gravity. You might say 'but I can see gravity working'. No, you see things falling to the ground.  Gravity is why that happens.  And we know that gravity is wrong, relativity does a more accurate job of describing why stuff falls to the ground.  We still use gravity to predict how the planets move because it is simpler and it is good enough for most things.