Even the worst mass extinction had its oases
arstechnica.com
arstechnica.com
There were a few interesting takeaways:
1) When people started realizing that these dieoffs happened there was a belief that there was probably a common cause like impactors, but end-Permian almost certainly wasn't an impactor like K-T was. There are several things that can kick-off an extinction
2) One thing that is true is that the extinctions seem to follow the same script. Lots of things can kick them off, but once they start going it's a rock rolling down a hill very quicky. End-Permian seems tied to the Siberian Traps basaltic eruption, but that eruption had been going for thousands of years before the dieoff started.
K-T definitely happened within years following the impact, but end-Permian seemed to be a "first gradually, then suddenly" as pollution from the traps put more and more stress on the biosphere until suddenly...
3) He posed the question: are we currently in an great extinction. He wrote that we are not because they look at the fossil record of really fundamental creatures (stuff like krill in the ocean) upon which the whole biosphere relies, and we're not yet seeing them collapse. But once such a collapse begins, it will be something that is unstoppable.
4) He thought that there is a big gap in our knowledge of survival and recovery. Why have none of these massive events just turned the planet into a dead world? How does life come back? Historically the early-Triassic was seen as a really boring thing to study because there's not much evidence of life in it, but understanding how life soldiers on through these "wasteland Earth" episodes is potentially a fertile ground for research.
* "Going on for thousands of years" - Dating the End-Permian has confidence intervals on the order of 30,000 years.
* Small size and diverse ecology almost guarantees survival of life. There is life basically everywhere we look, down to extremophiles living very slow lives in a random cubic meter of "solid rock" two kilometers deep. We have even evolved several chemical alternatives to photosynthesis as a primary energy source. Mammals and small birds deep in a cave somewhere appear to have been some of the only land vertebrates to survive K-T, and radiated out from there. Evolution does the rest.
Erwin discusses that theory but doesn't agree with it.
In any case, 1) there are other mass dyings that are definately not impactors like the oxygen crisis. 2) there are other basaltic eruptions on the scale of the siberian traps (like CAMP) where the cause is known and not an impactor.
But it's not proven to be an impact crater, nor is its age determined with any specificity. There's the lack of Iridium, and Erwin also had complaints about the modeling for an "antopodal convergence crack."
> End-Permian seems tied to the Siberian Traps basaltic eruption,
> but that eruption had been going for thousands of years before
> the dieoff started.
Biologists like to proclaim that things are gradual when they're really more likely sudden. This often reflects mathematical ignorance. For example, if the last specimin of a certain rare fossil is found in a stratum slightly older than the K-T stratum, does that mean it went extinct earlier than the K-T event? Probably not; it just means the fossil is rare so your sampling error is larger.
At the time of writing of the book it was "less than 60k years" which seems like a long time, but when the extinction was first discovered it was believed to be a very gradual change taking place over 10 million years, turns out that it was believed that end-Permian and end-Guadalupian were the same event.
As isotope dating has gotten more and more accurate, the length of time for end-Permian has gotten shorter and shorter. There's also other evidence that it was a very sudden event, evidence of fungal explosions for instance during the event suggesting massive amounts of decomposition.
In any case, as I said the P-T took "no more than 60k years" but the Siberian traps were erupting for at least 120k years before, so there's at least 60k years unaccounted for between the start of the eruptions and the start of the extinction.
Among other rationales: survivorship bias / anthropic principle. Of all the worlds in which a mass extinction event has wiped out all life prior to the emergence of a technologically-advanced species, there would be no (indegenous) witnesses to the fact. We are only here to ponder that question because utter annihilation did not occur.
You can make a similar argument about any catastrophic risk/event, and I was delighted to discover a few years ago that Richard Posner (former US federal judge) did just that:
By definition, all but the last doomsday prediction is false. Yet it does not follow, as many seem to think, that all doomsday predictions must be false; what follow is only that all such predictions but one are false.
-Richard A. Posner, Catastrophe: Risk and Response, p. 13.
<https://archive.org/details/catastropheriskr00posn/page/13/m...>
(Previously mentioned: <https://news.ycombinator.com/item?id=34647615>).
There are of course other points to be argued, including the resilience of life and its (possible) capacity to re-emerge multiple times. I suspect this was the case in the history of the early Earth, though of course there is vanishingly small prospect of finding any evidence of such an event.
Once life did become widespread (~3--3.5 bya) it does seem to have had remarkable tenacity.
AKA the Seneca effect. See https://terebess.hu/keletkultinfo/seneca.pdf
Not an expert on this by any means, but I always found this short series [1] quite fascinating on how cyanobacteria over a period of 200-300 million years coverted the planet from being methane based to being oxygen based, created the ozone layer and paved the way for photosynthesis, oxygen and life as we know it. I can't remember if I'm being too optimistic when I'm recalling bacteria doing something similar for the mass extinctions?
See also [2]
[1] https://www.bbc.co.uk/programmes/p09xj73n
[2] https://asm.org/Articles/2022/February/The-Great-Oxidation-E...
When clay forms in the ocean, it pulls calcium out of seawater. Calcium is normally balanced by two bicarbonate ions, so its removal causes the bicarbonate to shift back to carbonic acid/CO2. The ocean acidifies and CO2 is released. This has been called "anti-weathering", since it's the opposite of the normal process that draws down CO2 by weathering of silicates.
Sufficient injection of silicic acid and aluminum into the ocean could accelerate this process.
The ocean was acidic and anoxic and that was likely a cause of the extinction.
There definitely wasn't enough inorganic carbon released to fully account for the amount of warming that occurred (about 12°C). This was a big part of the book and highly technical (just the explanation of organic versus inorganic carbon was a chapter) so I'm afraid to try to summarize I think I'll get it wrong. But the author's theory was that methane was in the mix as well, released by cooking off carboniferous coal deposits.
https://pubs.geoscienceworld.org/gsa/geology/article/50/6/65...
The issue is not just the increase in CO2 at the P/T boundary, but the unusual persistence of high CO2 levels for 5 million years. In contrast, the CO2 spike from the CAMP flood basalts lasted only 300 thousand years. The paper proposes that the ocean became enriched in dissolved silica due to the loss of silica-secreting microorganisms (as indicated by lack of chert deposits during this time), and that this caused enhanced "reverse weathering" that kept CO2 levels high.
Well, you don't want to know how far you can safely bend over the cliff before falling down. I think attempts to gain such knowledge in a practical way should be explicitly banned.
Though I have extreme reservations about the current state of conservation science (on questions of nature and it's own agency), this is precisely why conservation is extremely important. We must protect what we have left to let nature adjust to what we become and want to be: https://eos.org/features/critical-zone-science-comes-of-age
Source: I work in palaeoecology.
While I think that a great many things can be learned by studying the relative few fossils discovered; making broad assumptions about ecosystems based on limited evidence seems like a bit of a stretch.
One way they do that is by focusing not on megafauna but on creatures that exist in immense numbers in a biosphere like insects or even smaller creatures. They also look at pollen and other biological matter that gets spread evenly.
They can also look at the effects life has on the structure and chemistry of earth. For instance, they know when oxygenation happened because there are chemicals in older rocks that can not form in the presence of oxygen, while there are chemicals in younger rocks that can only form in the presence of oxygen.
A big evidence that the end-Permian effected land as much as the ocean is the behavior of rivers. When plants are present, rivers tend to meander because plant roots hold onto the river banks. When plants are not present, the river is able to take the shortest path to the ocean. Rivers banks laid down at the end of the Permian meander, river banks laid down at the start of the Triassic do not.
* subject to relative flatness
But what an interesting thought, I'd never considered how river topography might indicate world conditions. So start of Triassic really was a blow to life!
Is this the right phrasing? I thought the whole planet was terrestrial
Not a distinction between sea and land life
The entire planet was very seldom, if ever, referred as "Terra". The correct Latin word for the entire planet was "Tellus" (whence the adjective "telluric"), whose likely meaning was "support" in the sense "the earth that supports us on it".
I think the first alien we'll find will be an extremophile bacteria or other microorganism.
With N=1, we know that life exists but not how common different development might be. Algae on another planet would suggest panspermia of common development pathways.
1.5C done, Onwards to 2C, should hit it before 2030.