Renewable vs. Non-renewable resources question

Hi everyone, I have a question regarding non-renewable resources in LOG 21 g.

If non-renewable resources is a limited supply, and cannot be renewed, should it have a perfectly inelastic? On a vertical supply curve, the Q is fixed, and only price can change.

I can pretty easily memorize that non-renewable resources has a perfectly elastic supply curve, but can someone explain the reasoning on the graph? Thanks!