Possible extinction event: nearby supernova

[jim mcnamara]

TL;DR Summary

The extinction event 359 mya that ended Devonian times may have been caused by a nearby supernova.

A popular science article on the end of the Devonian era examines the likelihood of an extinction event mediated by a nearby supernova.
https://www.sciencedaily.com/releases/2020/08/200818142104.htm

Per the article -
A convincing argument can be made by finding Samarium 146 and/or Plutonium 244 isotopes in rock strata from that period.

The proposed model includes what the authors call a double whammy:
First a blast of ionizing radiation, then a massive radioactive cloud of ejecta that persists over a long period. Both which could alter the magnetosphere of Earth and allow the solar wind to damage extant flora and fauna. The latter cloud effect could persist over long periods. Which matches the known geologic record of a ~100000 year decline in species diversity at the end of the Devonian.

My takeaway is this looks like a great research project.

Gather rocks from several sites around the globe, test for those two isotopes that do not naturally occur on Earth. The most likely results will be either clearly negative or positive if the experiment is well designed. A positive result is sure to spark intense criticism of the experimental design. New findings are often generate that. The downside is Geology has a long and tortuous history of downright ugly debate.

Ruling out other causes for the presence of those two isotopes would be intense. Meteors.

Finding anomalous abundances of weird elements in rock layers often is the result of meteor impacts. They may need to be ruled out. Meteor impacts can create layers. Thin layers with odd isotopes or elements have been found and used to help prove other hypotheses. Example:

Iridium in the K-Pg (KT is the old name) boundary layer caused by the Chicxulub impact, which made life hard for the dinosaurs. This layer is high in Iridium, rare or non-existent in most Earth rock. It is sometimes called the Iridium Anomaly.

https://en.wikipedia.org/wiki/Cretaceous–Paleogene_boundary
https://en.wikipedia.org/wiki/Chicxulub_crater
https://en.wikipedia.org/wiki/Iridium_anomaly

 

[Genava]

It is an interesting hypothesis, although it would be better to narrow it down to one particular event. In their paper, they are not distinguishing the Kellwasser event with the Hangenberg event (10 Myr separating them). Basically they are saying that their hypothesis could explain one of those events or even both. They should have stick with the Hangenberg event like it was suggested in previous papers.

Their paper: https://www.pnas.org/content/early/2020/08/17/2013774117

 

[Baluncore]

My takeaway is this looks like a great research project.

Gather rocks from several sites around the globe, test for those two isotopes that do not naturally occur on Earth. The most likely results will be either clearly negative or positive if the experiment is well designed. A positive result is sure to spark intense criticism of the experimental design. New findings are often generate that.

There is a huge volume of sedimentary rock near the surface of the Earth. Checking it randomly for exotic isotopes would be a very expensive process. Instead, mapping the contacts of formations that show a reduction in palaeontology, and analysing those for changes in exotic isotopes is a tractable project. But that is exactly what is done now, for example the Chicxulub Iridium.

 

[sbrothy]

I seem to remember one particular star which could go supernova any time with our Earth right in the line of fire. I cannot seem to find it now but here:

https://en.m.wikipedia.org/wiki/Near-Earth_supernova#Effects_on_Earth

is food for thought. ;)

 

[snorkack]

There is a huge volume of sedimentary rock near the surface of the Earth. Checking it randomly for exotic isotopes would be a very expensive process. Instead, mapping the contacts of formations that show a reduction in palaeontology, and analysing those for changes in exotic isotopes is a tractable project. But that is exactly what is done now, for example the Chicxulub Iridium.

The problem is that this presupposes the conclusion.
You should check the sedimentary rocks for changes in exotic isotopes that show no accompanying extinctions, too.

 

[Baluncore]

The problem is that this presupposes the conclusion.
You should check the sedimentary rocks for changes in exotic isotopes that show no accompanying extinctions, too.

If you are trying to correlate exotic isotopes with extinction events, you should sample the extinction horizon, along with the profile immediately before and immediately after. That will provide the necessary control.

The extinction event in a sedimentary section can be identified using a binary search for the step change in palaeontology. That comes naturally to a geologist walking out a formation, or examining the core from a drill hole. The same is not true of exotic isotopes that appear as a pulse in the section. Exotics cannot be easily seen while walking up stream beds, ascending rocky ridges, or climbing cliff faces.

It is not feasible to sample and analyse all candidate sections for a pulse of exotics that will probably be less than one millimetre thick. A one kilometre thick stratigraphic section would require one million samples. Some of those samples may contain exotic isotopes from meteorites that are local, not regional or worldwide. It would be impossible to find the exact same age strata, in different rock types in different locations, without the help of fossil evidence. If there is no extinction, then you have no reliable calendar.

You could reduce the analysis processing cost by bulking the milli-samples into one metre mixed samples, but there is nothing to say the exotic layer would be present in any of the samples, or in the section. Random sampling will blow your budget long before you get any usable data.