Excellent point; How do you know that conditions were the same before the curse as they are now? Are compounds breaking down different than compounds decaying. Could it be the difference between rust, and a catalyst?
By definition, decaying = breaking down into component parts.
http://dictionary.reference.com/search?q=decay
I thought that all creation was done at the same time. What did the bacteria eat? You would still need some sort of food chain, unless God just kept creating new food to eat for every single living being every day.
What does rust have to do with the food chain?
You realize how ridiculous this theory sounds, don't you?