I would imagine this is probably the source, which benchmarks using the last 200,000 years. https://www.prb.org/articles/how-many-people-have-ever-lived-on-eart

I would imagine this is probably the source, which benchmarks using the last 200,000 years. https://www.prb.org/articles/how-many-people-have-ever-lived-on-earth/ https://www.prb.org/articles/how-many-people-have-ever-lived... Given that we only hit the first billion people in 1804 and the second billion in 1927 it's not all that shocking.