Your "Scuba Earth" designation doesn’t match their trademark description, so unless they amend their description, I’d say this has been a rather empty threat. I’d sit on it and see and in the meanwhile, consult with a qualified attorney who knows this type of law as to whether you need to apply for your own trademark.
I, personally, think you have a superior product to PADI’s application and I’ll continue to log my diving experiences on this site as long as it continues to work. I hope it works out to be no big deal for you in the end. :)