[Vaevictis Asmadi]

Originally Posted by ericthered

I'm not sure how complete the die-off will be. Yes, UV radiation is a powerful sterilizer. But life is suburb at surviving. The deep sea vent life, at least, will come out alive. The food chain at the bottom normally fed by the top will survive for a long time by cannibalizing itself, and its got a slow metabolism in the first place. The plankton locked in Antartic ice will survive. I'm also not sure if there is a depth where visible light reaches but the deadly UV varieties do not. That last category offers some hope for sustaining human life, as well as for repopulating the land once UV goes down.

Yes, a couple meters below the water surface appears to be photic enough for life but mostly safe from UV (A thru C).

But oxygen would get depleted very fast in the water. All that dead material would be a bonanza for any decomposer that can survive UV by being buried in its food and/or catch dead stuff falling into the aphotic zone. Deep ocean anoxia also appears to have cascade effects that could kill huge swaths of the biosphere -- it was probably a significant factor in the Permian mass extinction. With decomposition overtaking photosynthesis both on land and in water, I'd expect a CO2 and CH4 increase -- though when offset by a rapid end to industrial activity and possible darkened skies, it may not accelerate global warming.

Some marine life would survive, after all it survived a 96% die-off at the Permo-Triassic. But I think that all or nearly all land and freshwater life would be gone. Keep in mind that Earth plants are exquisitely vulnerable to radiation, compared to animals. Unless humans already had self-sufficient underwaters cities, I doubt any of us would make it. People would have to last on stored food until the ozone layer fully recovered, before agriculture would become viable again. Then they'd have to cope with soils that might be changed -- essential microbes and fungi might be gone, replaced by large quantities of decomposers.