Earth hit a major milestone in November. According to United Nation (UN) statistics, the world population has reached eight billion. That’s an immense number. To count all the people on the planet, one by one, a second at a time, would take 253 years.

Boom!

The population broke the one-billion mark in 1804, 300,000 years after human beings first appeared on Earth. It reached two billion only 123 years later, in 1927.