Nature is rarely linear. Most functions and populations and processes are curvilinear.
Right, it’s a “log-linear” plot, where taking the logarithm of both sides of an equation straightens it out. What strikes me right away is that the earth comes along and it doesn’t do anything to the graph, lol, almost like it doesn’t make a whit of difference in how the process progresses, when obviously, it must. You’re not going to get whales, people, trees, etc., evolving in deep space. So they could have at least changed the slope at that point.
Not linear. The ordinate of the graph is log. Nature favors logarithmic growth functions.