I too was trying to find the date of this photo this week. To narrow your time span, the first aerial photograph (also from a balloon) was taken in 1858 in France. So this photo had to have been taken after that point.

As someone who does speak native English, no clue. My best guess is that it is a typo. I think it was supposed to be $40m.

Most of the "chasm of ignorance" is the stuff we know that we don't know. We don't know what dark matter is made of. We don't know what dark energy is. We don't know how to reconcile quantum mechanics and general relativity.