OK, just in case the link doesn't work for you (or it's forcing you to sign up and you don't want to...OR THEY HAVE HOPEFULLY PUT A HALT TO THE CRAZY):
Are you as flabbergasted as I am?? My email to customer service said, in part:
The Egyptians (to pick an old culture at random) would beg to differ with you. And remember that whole Y2K problem we had? Did you know that the "Y" in "Y2K" stands for "Year"?
My mental capacity and imagination are unable to stretch far enough to come up with a plausible explanation for what they're thinking. Earth Day was first celebrated in 1970 in San Francisco, so they can't have meant "40". Even strictly literal Biblical interpretations would say around 6,000! It wasn't a typo, because I got an email with different text that referred to the "400th" birthday and hoping we could make it to our "401st".
MAKE THE STUPID STOP!
[ETA]: Groupon customer service emailed me back and said that the copy was meant to be humorous. What do you think? Did it come across as humorous or just nuts?