If resources were not limited economics would have exist as a disipline?

Yes, because while the resources are not limited the skills needed to extract or refine or utilise those resources are limited. For example, the ability to "speak a language" as a resource is unlimited but the ability to teach someone to use that language effectively IS limited hence there will be an economic force governing that subset. Same goes for iron ore, if it was common, lay around everywhere like dirt you'd still need someone with the time and skill to refine it which would be an economic force.