The problem of assigning a specific date for man's "causing fundamental shifts in the state and functioning of Earth Systems" is that the tools and methods we currently utilize for such endeavors are built upon cruder and less efficient tools of a previous era. I recall reading something from an old game "Sid Meier's Alpha Centauri" along the line of, we don't simply take a handful of sand and produce microchips; we make simple tools, which lead to ever-increasing complex tools and every iteration of this process must be followed.

The first instance of man harnessing fire was the moment of his realization that he can shape his surroundings by the force of will alone. One could argue that manipulation of fire was the germ of the conceptual framework that shapes our world-view today.