Paper result validation and the scientific method in earth science
Let's start with the trivially true: programming is not earth science; earth science is not programming. Programming is one tool of many in earth science. In programming, the end result is the program itself. In earth science, that's never the case: but one end result is algorithms developed that inform us about the real world, and implemented in a progam.

What if there is a bug in a peer-reviewed paper? Well, of course there is, just as there are bugs in pretty much every program that does anything useful in the real world. So what?

Validating source code is  the domain of programming. Validating algorithms and observations is the domain of earth science. Re-running someone else's code with the same input data is barely any kind of validation at all, and rarely the interesting kind. Taking someone else's algorithms and implementing them yourself, that's the sort of validation I see across the physical, life, social sciences.

So I don't see someone else's source code? No big deal. Indeed, that's often a good thing: it means I can genuinely clean-room their algorithm.