It is remarkable how certain industries are protected against shocks, this reminds me of countries who easily bare financial crises as a result of being primary food exporters (NZ). What is even more interesting is the difficulting of fully getting rid of humans in an econmic endevour (latter part of the chart).
Regarding your point on linearity, this chart does show a linear decrease as of 1800. However lets say farming activity halved as a portion of all jobs in the first 100 years, in the latter hundred years it decreased with a multiple of 25. So in the first half it was transformed by X*1/2 and in the second half X*1/25. Is this still linear ? I was wondering about this phenomena, is there something like absolute and relative linearity or exponentiality ?
It seems that the percentage change then is exponential