How thick would the atmosphere have to be to block all the sunlight?

this is a question I haven't been able to find an answer to anywhere. How thick would our atmosphere have to be for the surface of the planet to be completely dark? Is that even possible? Thank you!

• Is this question aimed at an atmosphere of 21% oxygen and 79% nitrogen, with no clouds in it? – David White Jun 13 '19 at 0:25
• Yes absolutely! – Timothé Jun 13 '19 at 16:55

Wikipedia says that “At most about 75% of the solar energy actually reaches the earth's surface.” You can roughly estimate that if the atmosphere were $$n$$ times as thick, the fraction would be $$(0.75)^{n-1}$$ compared with what we get. For example, if the atmosphere were 20 times as thick, sunlight would be reduced to 8%; at 20 times, to 0.4%; at 30 times, 0.02%. It never gets completely dark, but at 100 times you get less than one trillionth of the sunlight we get.