previous post on these pages.
A couple of weeks ago Bond & Scott published a paper in the rather wonderfully named scientific journal 'New Phytologist' that discusses how flowering planets, or angiosperms, spread during the Cretaceous some 65 to 145 million years ago. The novel aspect to this work is the suggestion that critically during this period, because of an elevated atmospheric oxygen level compared to today - perhaps to 25% rather than our paltry 21% by volume, surface fires were much more pervasive. I talked about this general phenomenon a while back.
So, the picture goes like this. Wildfires (well, I guess every fire was 'wild' during the Cretaceous) would have been significantly more frequent with higher atmospheric oxygen. This would have posed a significant challenge to surface plant life. Long-lived and slow growing species, like larger conifer trees - which have an ancient lineage - would have a hard time regenerating their populations fast enough. Imagine a cosy little spot, a fire rips through, everything burnt to a crisp. Seeds arrive, new plants grow, but sure enough another fire comes tearing across the land. Only those plants that had grown fast enough to mature and dump out the next round of seeds (carried off by wind and newly minted mammals and birds) would stand a chance at producing another generation. It's a vicious cycle, the fast growing angiosperms (one presumes helped along by insect and animal pollination) not only outrun the fire cycle, but they quickly produce the next round of fuel.
The upshot is that flowering plants don't get as much competition for resources from the previously dominant types of vegetation - in essence the weedy daisies win the day. The evidence for all this combustible carnage lurks in the remarkable charcoal deposits, and charcoal fossils from this geological period.
It's another example of the incredibly intertwined nature of life on a planet, and another great example of the constant 'what ifs' of evolution. Would an Earth that had always kept a low oxygen level have ended up with flowering plants - and the particular effect this implies on continental albedo and biosignatures?