There are so many concerns and theories for "the end"

A new spread virus "A New Plague" some believe could be formed by altered versions of small pox disclosed if it's still out there, in the wrong hands.. spread through subways airports any large traffic area.

Super Volcanoes around the world erupting causing a new Ice age globally.

Nuclear warfare.. 2 nukes crossing causing a darkness and dying of plant life globally.

Global Warming of course..

But really, how long have these theories and concerns been developed?

Can any of them really be that accurate? Our "Ancestors" I'm still not sure about history myself but that's my own conspiracy theory..
How could they possibly have knew, as SignGuy said.