The Earth
goes through periodic ice ages
within the context of a
greater ice age that we
are in the midst of now 
these ice ages last about
100,000 to 110,000 years...
these periods of ice
are punctuated by periods
when this ice retreats, sometimes
disappears utterly...
These periods last about
10,000 to 12,000 years...
We human beings popped into
being at the very beginning
of this "interglacial"
about 12,000 years ago...
We Humans now number
about 7 billion souls
and we now approach the
carrying capacity of the Earth.
We are due for another
Ice Age, and soon
geologically speaking.

You do the Math

(agriculture and cities...civilization began about 10,000 years ago,
man has been around far longer, if only briefly...in the cosmic
scheme of things.)
I ponder on the fact that the spot where I was born is usually
covered by many hundreds of feet of ice. A spot that today feeds many of
the over 7,000,000,000 now alive.