World population milestones went unnoticed until the 19th century, since there was no reliable data on global population dynamics. It is estimated that the population of the world reached * one billion for the first time in 1804; * two billion in 1927, 123 years later; * three billion in 1960, 33 years later; * four billion in 1974, 14 years later; * five billion in 1987, 13 years later; * six billion in 1999, 12 years later; * seven billion in 2011, 12 years later; * eight billion in 2022, 11 years later Old estimates put the world