The Great Dying has been dated to 252 million years ago for some decades now, but its cause(s) remain/s elusive. Part of the problem is that although they've nailed down the end of the extinction era, they hadn't constrained its start. Of course the start is what you want if you're looking for cause.
Last week this blog got a visit, I think, from the Triple-I Blog. I went to the main blog and found it, basically, an aggregate of news-releases. But hey: why not. I looked at it today and found this announcement, pointing to Michael R. Rampino and Shu-Zhong Shen, "The end-Guadalupian (259.8 Ma) biodiversity crisis: the sixth major mass extinction?" in Historical Biology (2019) DOI: 10.1080/08912963.2019.1658096.
When you go that far back, it's not easy to tell one mess from another. And indeed I have seen charts of the extinction that looked "hump backed" over a span of the end-Permian.
If these guys are right, we're over that first hump, so to speak. The Emeishan Traps were the trigger for the 259.8 Ma disaster and then, a few million years later, came another disaster which hit the by-now genetically bottlenecked survivors.
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