Does syncing your iphone iOS calendar with Google calendar overwrite what's currently in your iPhone calendar?

I have been syncing my iphone calendar over icloud. I want to sync it with my google calendar now, as well (my google calendar is currently blank and has no entries). If I set this up, will my iphone calendar get overwritten by my google calendar, ultimately erasing everything? The instructions I'd be using to sync my iphone calendar to my Google calendar are at the link below:

http://support.google.com/calendar/bin/answer.py?hl=en&answer=151674

Thanks!