Why might an author have more than one purpose for writing?

I’m just thinking something from the top of my head so it may not be much so if weathering didn’t exist, there wouldn’t be anything to break up earth’s crust naturally. so by assumptions, the rocks on earth would be larger than they actually are since there’s nothing to break them up into smaller parts.overall, i’m not really sure, but all i know is that it’ll mess up the rock cycle that we have now.hoped this .