Pop Quiz:
If half of the worlds population was wiped out, what year would that take us back to in terms of population?

Spoiler Alert, click show to read: 
1965


If nine-tenths of humanity were wiped out in a zombie-octosquid from outer space plague, what year in terms of human population would we be at?

Spoiler Alert, click show to read: 

Approx 1700 AD


We would have still all the technology and knowledge about our world...