It took thousands of years for the global population to hit 5 billion, which happened in 1987. Some 32 years later, we're closing in on 8 billion.
원문출처 : https://www.cnn.com/2019/07/11/world/world-population-day-trnd/index.html
원문출처 : https://www.cnn.com/2019/07/11/world/world-population-day-trnd/index.html