I'm given 2 theories.
Person A - The world is old. We've learned the rate at which radioactive isotopes decay, and by looking at them in rock, we can determine the age of said rock. Therefore, we can also determine the age of what's inside and around this rock. In addition, it appears that by doing this, we can see how humans and other animals have evolved over time.
Person B - The world is young, and there was no evolution, because the Bible says so, and you should trust the word of God.
I'm thinking for myself, and if forced to choose one, i decide that person A is most accurate. (And again, I believe that God does have a part when describing how life was formed.)