@pschwede Thats a fine theory to put forth and all and im sure people made such theories int he early days when they didnt know about climate change and the topic hasnt been investigated.

So why not go and investigate yoru theory. Go look at the fossil record around plants and see where their relative biomass high and low periods are and plant extinction events and see if they line up with the chart and validate your theory.

Obviously you will find that your theory is easily debunked but int he name of science if you feel it is a valid explanation i do encourage you to research it rather than just assume it to be valid.