An NPR report by Christopher Joyce in the cell phone news reported earlier this week related information about a Smithsonian exhibit's information related to the greatest extinction event known in the history of the earth. The end of the Permian event about 250 million years ago nearly extinguished life on earth and was referred to as the "Great Dying".
Volcanic activity, with probably some help from asteroid impacts, reduced ice cover and made atmospheric pollution increase global temperatures far beyond the state we now have. Cold climate animals could no longer survive in the arctic regions where they may have thrived on the land mass prior to its breakup into the present continental condition.
Surface temperatures and absence of polar ice made the cold water input to the ocean bottom stop, or be very slow to replace the bottom water, but the hot surface water would become hotter and make a thicker layer. Water from polar regions would presumably be warmer and lighter than abyssal water, although colder than water from most of the ocean. That water would have an intermediate density that would replace water of similar density under or in the thermocline. The abyssal depths of some ocean basins away from asteroid impact would probably remain relatively unchanged and give refuge from the "Great Dying" to pogonophorans and other species that would provide life to shallower waters after conditions improve.
The end of Permian extinctions were the worst of the Paleozoic Era and exceed the species deaths of the second worst extinction episode at the end of the Mesozoic Era's Cretaceous Period about 65 million years ago. Pre-Cambrian extinctions may have been more deadly in the two billion years of Pre-Cambrian life, but it is unlikely for much evidence to survive geologic processes.
DEEP SEA PHYSIOLOGY
Reports of high rates of oxygen consumption by microbes deep in abyssal sediments seem to be impossible and require a different explanation, although thermal vents and heat from magma could have some interesting physiological implications of which I am unaware.
The rapid growth of giant tubeworms at thermal vents seems dependent on chemosynthesis by bacteria in special tissue as a source of nutrients; like normal pogonophorans, giant tubeworms lack a functional gut.
The reduction of diffusion in water under great pressure that I have suggested as the explanation for the dramatically slow aging of deep sea organisms would seem to be greatly modified at higher temperatures of thermal vents and presumably deeper sediment warmed by the core of the earth if the reported rates are correct.
The abyssal region remains a refuge under siege from plastic and other pollution that may survive our worst climate-altering assaults if anyone will be around a few million years from now to notice.
Joe Engemann Kalamazoo, Michigan June 8, 2019
