Extinction event 42,000 years ago probably not due to UV
So 42 may not be the Answer to Everything after all ...
An article reported recently in Australia makes interesting reading. The paper that it cites was just published in the prestigious US journal, Science and makes the claim that an extinction event 42 thousand years ago 1 was caused by increases in UV radiation associated with a reversal in the Earth’s magnetic field.
In a nod to The Hitchhikers Guide to the Galaxy - created by Douglas Adams - the authors cleverly dubbed it an Adams Event.
That’s a nice touch, but does the theory hold water?
I was interested but had my doubts, and passed it by a colleague (who prefers to remain anonymous - at least for now). Here’s an excerpt from his ‘shooting from-the-hip’ response.
I find their results highly speculative. If I understand correctly, the major changes observed during the “Laschamps” period are attributed to the following mechanism, explained at the top of page 4:
“Our results yield a large increase in atmospheric ionization from Galactic Cosmic Rays, resulting in an enhanced production of hydrogen and nitrogen oxides (HOx and NOx, respectively) (Fig. 2, A and B) down to very low altitudes. The increased HOx and NOx concentrations influenced ozone levels over the entire atmosphere, decreasing the O3 mixing ratio in the stratosphere (~5%) while increasing the O3 mixing ratio in the troposphere, with the greatest changes observed over Antarctica (~5%) (Fig. 2, C and D).”
I find it hard to believe that a modest 5% reduction in ozone caused, amongst others:
Megafauna extinction in Australia (even though humans made it to Australia at about the same time and it is well documented that large animals got extinct on pretty much every continent after humans set foot on it).
The onset of cave paintings because prehistoric humans sought shelter in caves to avoid getting sunburnt as the 5% ozone change led to “an increase in UV-B to potentially harmful levels.”
The extinction of the Neanderthals (even though they also had to compete (and possibly interbred) with modern humans at around the same time).
Their results are all based on results of their model and results depend on many assumptions, which are hard to validate.
Reversal of the Earth’s magnetic field occur on average every 200,000 years and according to https://www.nasa.gov/topics/earth/features/2012-poleReversal.html:
“The last time that Earth's poles flipped in a major reversal was about 780,000 years ago, in what scientists call the Brunhes-Matuyama reversal. The fossil record shows no drastic changes in plant or animal life. Deep ocean sediment cores from this period also indicate no changes in glacial activity, based on the amount of oxygen isotopes in the cores.”
Why should the short-time reversal during the Laschamps have led to major extinctions when the “major” reversal 780,000 years ago had apparently little effect?
I give the authors credit for their humor, though, for coining the term “Adams Event” in reference to the writer Douglas Adams and “42” :😊
Good points well made mate!
As another colleague noted, the increase in UV radiation due to a 5 percent reduction in ozone at mid latitudes isn’t huge anyway. It’s similar to that from just moving just a few degrees closer to the equator. So it can be compensated by moving a few degrees away from the equator: a migratory feat that can accomplished for most within a few days or weeks.
Could it be that 42 is not the answer to the Ultimate Question of Life, the Universe, and Everything? Surely not. Perhaps just everything except that extinction event? 😊
Updated June 14, 20201. In the original version of this posting, I mistakenly said 42 million rather than 42 thousand years!