What was the estimated temperature on Earth before human activity?
There is no one estimated temperature on Earth before human activity. Does human activity mean the Industrial Revolution? Facts are that global climate goes through periodic cooling and heating, on both millennial, centurial, and decadal scales. This isn’t to say that I’m denying that recent global warming may very well be man-made, it’s just that temperatures were always changing. This goes double when you try to get a global temperature, because climate patterns can be localized in any given year that might, for instance, drive up the global temperature, even though most of the world was at its “normal” temperature. The first link below has a lot of information about the periodic heating and cooling.
