The terrestrial Frasnian/Famennian mass extinction event?

We know life on Earth constantly evolves with continual extinctions and their replacement by new species. Think of it as a football club. To remain successful the team has to constantly change by recruiting new stars and transferring out failing players because of age, lack of success or injury. However, there are times when this constant churn of extinction and evolutionary replacement is interrupted by catastrophic collapses in total species numbers. These are mass extinctions. At these times entire groups of plants and animals disappear during a geologically short time. Good examples are the dinosaurs at the end of the Cretaceous and the trilobites at the end of the Permian, the greatest mass extinction of them all. There are 5 of these big mass extinctions during the last 500 million years. Some we know understand better, such as the meteorite impact at the Cretaceous/Tertiary boundary (65 million years ago) and the relatively short and severe ice age at the end of the Ordovician Period (440 million years ago). One mass extinction event that we still don't understand occurred ~376.5 million years ago in the later part of the Devonian Period. This, was the Frasnian/Famennian or F/F event and was a greater extinction than that which killed the dinosaurs. Palaeontologists have suggested many causes for the F/F event ranging from meteorite impacts, massive volcanic eruptions, global warming and global cooling. Life on Earth has even been suggested as the cause with the combined effects of giant reefs and land plants both locking up carbon dioxide and causing global cooling and an ice age. Land plants were then relatively new to the Earth and were both spreading rapidly across the land surface and increasing in size to become significant trees and were therefore potentially locking up atmospheric carbon dioxide. For most of the other mass extinctions we now better understand the causes by being able to see the combined effects of extinction on plants and animals from land and sea. However, for the F/F event we only have a very poor record of plant numbers through the time of the extinction and in particularly do not know whether any extinctions occur at exactly the same times as the extinctions that killed the sea life. Fortunately we have discovered a new rock unit in northern Russia that was deposited on the edge of the sea and contains a good record of land plants through the time of extinction. We can do this because we are studying the microscopic spores (just like pollen) from the plants. These spores are very resistant and can be found and extracted from rocks even when the parent plants are not fossilized. Unfortunately this new rock unit is mostly buried in the bank of a river. But we can get a solid core of rock by using a drilling rig. We can then use this core to extract the fossil spores and count them in closely spaced samples through the rock unit. This will show when the plants became extinct, for example was is slowly through time with no new plants evolving, was it suddenly with many of the the plants becoming extinct together or as a series of shorter duration successive crises with a few becoming extinct each time. We can then match this record to the extinctions in the sea. We have already studied rocks in East Greenland which during the Devonian was in the southern hemisphere arid zone. This direct record of land climate shows times of severe aridity when the spores became simple and rare. Using these spores we can compare this direct climate record to the borehole from Russia together with the marine extinctions to try and prove that cool aridity was a cause of the F/F mass extinction.