I once saw a graph of oil production/consumption over the last 100-150 years. Interestingly the curve is a smooth exponential right up until the late 1960's and then it gets ugly jaggy linear.
Say what you will but I think that's really significant.
And it possibly still can. There is mentioned in that link of the theory being controversial due to automation, where there ends up being less workers and more production.
napkin math. Say we start with economy size A and a year later we have A+P. The profit rate is P/A. Whole economy-wise the P comes from people doing/producing something. Next year same people doing the same would produce the same P. Thus profit rate fell - it is now P/(A+P). As a result we can see that the profit rate can be increased by increasing output - ie. P(next year) > P(this year) due to productivity increase (thus automation) and/or labor force growth (population growth).
Say what you will but I think that's really significant.