It's a real shame that so many of our datasets start out in the middle of the 20th century when people used atmospheric nuclear tests to light cigarettes [0] and then drove home in their lead gasoline fueled trucks to eat in lead painted dining rooms food grown under the protection of DDT. I would guess if one looked at the chemical environment for all of human history, somewhere between 1950 and 1970 would probably be the absolute furthest from the baseline.

[0] https://www.wearethemighty.com/mighty-history/physicist-lit-...