We humans flawed and so are our current theories. We will never have the answers or facts for life's most important questions. The Bible has contradictions and so does the theory of evolution. What goes for one goes for the other.
That's why we have theories and hypothesis. Flat earth was a hypothesis. Through observation the earth was believed to be flat. Then through observation and attempts to confirm the earth was flat we discovered that it was less likely that it was flat and more likely that it was round. Through constant observation and thorough testing including analyzing stages of the moon, the stars, the horizon and venturing around the world we found enough evidence to conclude that the earth is round. This is when it is no longer a hypothesis and it becomes a theory that the earth is round.
Evolution is also a theory because there is enough evidence to show that it is real and constant testing to attempt to prove it wrong has only proven it more true. That's how scientific theory works.
A scientific theory is a well-substantiated explanation of some aspect of the natural world or Universe, based on knowledge that has been repeatedly confirmed through observation and experimentation. This is why Gravity is considered a theory.
The good thing about science is that when a contradiction is found then science attempts to figure out why the contradiction exists. For this reason there was contradictions in evolution and contradictions appear now and then but each time they do science eventually finds a way to explain them.
The issue with the Creationist belief of a young earth is that the contradictions are too many and rather than investigating the contradictions to their belief they ignore them.
