You ever wondered why in Adventure time there is ruins of modern day stuff everywere and why Marsiline and the Ice king are been alive for 30,000,000 years and there were zombies.
On the year 2009 a nuke-bomb blowed up and droped the humans to 570,000,801,044,000,094 to 4, 80% of the humans were zombies. In the year 30002009 Finn, Marsiline, and the Ice king are the 3 last humans on earth.