If the law had been intended to apply to oil drilling and specific pollutants, it would have named them. Or at least named specific types of pollution. Instead it appears to have been deliberately written broadly to capture a wide variety of forms of environmental degradation, perhaps including some not discovered at the time of writing.

The connection between atmospheric CO2 and warming was actually identified as early as around the year 1900.

I wasn't around then to have a sense of the broad social awareness of things, but I've gotten the impression that the science was fairly obvious before the 1970s.

Except it literally was just tested.