Stardust Memories: Reading Evolution and Extinction in the Stars
One of the fundamental lessons of the fossil record is that extinction happens. Translated via the flick Forrest Gump - “Shit happens”.
(A cool movie, although the dude who made it may not be so cool: note the products and savoir faire of film makers is a leitmotif of the blog.) Quite frequently (every 5-10 million years, more or less regularly) this plays out in dramatic pulses of extinction (part of what Elisabeth Vrba of Yale University termed “Turnover Pulses”) involving a good portion of species in local regions disappearing in a geological instant. More rarely, but still at least 5 times in the history of animal life over the last ~ 500 million years, there have been even more cataclysmic mass extinction events, involving the rapid elimination of species at a global scale. Intriguingly, some component of each of these types of events may have been triggered by stellar explosions. Why does this matter for our understanding of evolution? The existentialist in us decries that nothing matters: yet we persist in plugging along. Maybe life is like this too? It continually gets smacked down, yet at least thus far has inexorably “come back for more”. It is like the Sisyphean drama that Charles Schulz so masterfully scripted in the ballet between Lucy, Charlie Brown, and that most highly renowned of oblate spheroids, the pigskin of American football.
Darwin closed his magnum opus with a masterful quote:
But he could have equally closed it with the more lugubrious phrase:
“forms most beautiful and most wonderful have been, and are being, DRIVEN TO EXTINCTION.”
We suspect that “On the Origin of Species … ” is much more uplifting than “On the Death of Species” (though in our modern world the latter may be more timely). However, Darwin’s vision of the origin of species very much involved one species as it originated competitively wedging out another species that had previously existed, given that he held that there were a limited number of stations of nature and thus resource space available. Consequently, emphatically in Darwin’s worldview evolution and extinction were intertwined and could perhaps be seen as two sides of the same coin. This was carried even further by the aspect of Darwin’s worldview, and the Neo-Darwinian world view, that emphasized the notion of what one of us (NE) and Stephen Jay Gould termed phyletic gradualism, whereby species would slowly and gradually evolve into the station of one species and out of the station of another species (what is called phyletic speciation conjoined to phyletic extinction).
We aren’t saying that this aspect of Darwin or the Neo-Darwinian view is valid. In fact, it is very much debated whether there is a cap on the number of species that can persist in any one setting or on the globe in total. Further, it is not generally accepted that the evolution of one species requires another species to be competitively driven to extinction: actually, rarely does one species competitively drive another species to extinction during any portion of its history. And lastly, for our present purposes, we only need mention that the phyletic gradualist perspective is supported by next to no evidence: our own favorite quote on this is Darwin’s quietly desperate note on the lack of evidence supporting his early embrace of gradualism (1837-39) in one entry in one of his Transmutation Notebooks: (paraphrasing) “...surely Mr. Lonsdale has a few examples....” Mr. Lonsdale, manifestly, never showed up with the goods.
Instead, today while it is well recognized that speciation and extinction events appear to be clustered in time, as Elisabeth Vrba recognized with the aforementioned Turnover Pulses, the causal mechanism driving this clustering is not competition but rather environmental change which in turn influences the geographic range of species and their likelihood of going extinct or producing new species.
What causes this environmental change? To a greater or less extent, the answer often lies in astronomy. Particularly in the case of the Turnover Pulse hypothesis, it is Milankovitch cycles governed by the dynamics between our sun and the changes in the amount of solar radiation the surface of Earth receives due to changes in the orbit, rotation, and axis of our planet that transpire over the course of tens to hundreds of thousands of years. We note that there is excellent evidence of these preserved throughout the geologic record. For instance, consider the Devonian of New York State, in our humble opinions a first-class time period, a first-class place of subtle yet sublime beauty.
Indeed, the virtues of this area have been extolled by many, including the exponents of the Hudson River School of Art.
Parts of this real estate (that we and especially NE prospected in search of trilobites) were blanketed very long ago by new and reworked sediments, the detritus from a mountain range whose uplift was triggered by the collision of continental plates. It was in this area that Peter Goodwin and E.J. Anderson, of Temple University, identified “punctuated aggradational cycles”, which they suggested were caused by Milankovitch driven oscillations in sea-level: https://www.jstor.org/stable/30062075?seq=1#page_scan_tab_contents . (These cycles are preserved in oozy lime muds in the segment of the Devonian deposited before the aforementioned continental collision.) Although the virtues of the punctuated aggradational cycle or PAC hypothesis may not have been widely espoused, we thought it was a pretty cool idea back in the day. Although it has not yet been examined, it would be interesting to see if these Devonian climate cycles produced corresponding pulses of speciation and extinction, like Vrba’s Turnover Pulses preserved in the latest geological intervals of the African fossil record. If they did not it may have been because the Devonian denizens of the Catskills were marine invertebrates such as brachiopods and trilobites, that were less likely to become geographically isolated and speciate than Vrba’s tropical mammals.
Other types of more calamitous “astronomically driven” environmental changes happen more rarely. There is of course the giant meteorite of end Cretaceous fame, that we shall here eschew and instead turn our purview to a category of events more properly construed as astronomical.
Joni Mitchell said “we are stardust … “
Billy Ward and his Dominoes crooned of “Stardust”, as memorialized in perhaps the most brilliantest and coolest of all flicks: Goodfellas.
A flick we would assert was made by one very cool dude! although alas we have never met academy award winner Martin Scorsese.
“Stardust” has in fact been performed by many artists over the years, and a more recent and especially moving version features Aaron Neville.
And finally, all music aficionados should know well of “Stella by Starlight”, especially any version by Miles Davis.
Well, sometimes a star across the galaxy explodes in a Gamma Ray Burst (GRB), shown schematically here:
releasing a pulse of energy lasting 30 seconds or so (gone even faster than Nicolas Cage in this movie:
a flick whose merits we might castigate except for the fact that good old NC also loves trilobites) measuring 10 to the 46 watts and equivalent to all the light from all the stars in the universe. As such, GRBs represent the most powerful explosions known.
A gamma ray burst and an Ordovician calamity
Based on research one of us (BSL) conducted in collaboration with physicist Adrian Melott of the University of Kansas and colleagues https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/did-a-gammaray-burst-initiate-the-late-ordovician-mass-extinction/F37A58C811EB82496CEF6CF989159807 a GRB 440 million years ago and 6,000 light years away may well have played a key role in causing the mass extinction at the end of the Ordovician period. This mass extinction spelled the end for perhaps 70% of all marine species, including many representatives of the group we know and love, the trilobites. For instance, never again would this charismatic species
from the Ordovician of Oklahoma scurry over the seafloor.
Whether a GRB precipitated the end Ordovician mass extinction is not yet settled, but understanding by astrophysicists of past and present rates of star formation and explosion suggests that a GRB should have occurred at least once in the last billion years in our galactic vicinity (about 6,000 light years away, give or take). We can also be fairly confident that there was never a proximate GRB, let say 500 light years away or less, over this same interval because it would have literally incinerated the face of the planet:
and wiped out life entirely; the ultimate mass extinction that thankfully never came to fruition.
Citizens love paleontology, and when you combine fossils with exploding stars it represents a subject matter that earnest folks everywhere find hard to resist. Indeed, when our hypothesis on a GRB and the late Ordovician mass extinction first was published one of us (BSL) received a phone call from a sincere employee of some western state’s Department of Fish and Wildlife enquiring about the threat GRBs represented to various birds of prey.
Thankfully, his concerns were allayed in short order. BTW, in further homage to “Donnie Brasco”, a pretty good flick but a really great book, we double down on the previous video and add - “what does ‘Forget about it’ mean”? Sometimes it means the stewards of California condors can sleep peacefully at night knowing that a cosmic catastrophe in a spiral arm of our galaxy is far down on the list of perils confronting endangered representatives of the Class Aves.
Megalodon’s gone: A supernova did in Jaws?
Another more recent and different type of stellar explosion also seems to have left a signature in the geological record and a stamp on the history of life: supernovae.
In particular, about 2.6 million years and 150 light years away a supernova exploded (intriguingly, and perhaps not coincidentally, this is when Vrba’s most pronounced Turnover Pulse occurred). This prodigious explosion (supernovae are less violent than GRBs, releasing only one hundredth the energy, but that’s still 10 to the 44th watts of power) may be associated with a decent-sized extinction event in some big animals (but since there aren’t that many big animals that doesn’t translate into a mass extinction). Because they are less violent, and their explosive energy is released outwards in a dispersed blast radius rather than concentrated, directed beams, faraway supernovae do not comprise the collective cosmic threat to us that GRBs do. Geologically recent (and astronomically nearby) supernovae can leave behind discernible geochemical signatures such as the radioisotope Iron-60 and an Iron-60 spike is present in 2.6 million-year old sediments. Adrian Melott and colleagues helped draw the connection that this spike in the sediments closely corresponds to the time horizon when several large taxa disappear from the fossil record, most notably, for charismatic fauna purposes, Carcharocles megalodon or Megalodon for short.
The types of radiation released by a supernova would be most detrimental to organisms with large body size, and the big as a bus Megalodon is nothing if not large.
Okay, sorry about that one, but it is part of the theme …
Rosa Compagnucci of the Universidade de Buenos Aires and colleagues also noted this connection and argued that a supernova at this time may have helped influence the extensive climate change at the time by stimulating global cooling. We note that other phenomena, such as the closure of the Isthmus of Panama due to the collision between North and South America, have previously been suggested to have played a major role in causing the Earth to enter the Icehouse conditions of the Pleistocene, but wouldn’t it be fascinating if a distant exploding star also played a role in fomenting this change? Melott and Brian Thomas of Washburn University further described some other effects a nearby supernova might have on Earth, including an uptick in lightning strikes and concomitant fires.
Of course this is an area of active research, and surely more insights will continue to be made regarding the role of exploding stars in the history of life. Might the entire thing even be a joke? Who knows? Yet returning to our leitmotif, we are brought full circle to our title and the 1980 eponymous film:
which we didn’t quite dig. We “liked the earlier funnier films.” E.g.:
And to further return to the dual aspect of our theme on films and filmmakers, we must say Woody seems to be one tres weird, uncool dude,
who happens to have made some great movies. And like him, we “don’t want to achieve immortality through (our) work, (we) want to achieve it by not dying”.
With that thought in mind, while the Sun may just be another star, it’s our star, and may it never explode.
This blog was written by Bruce S. Lieberman and Niles Eldredge. The manager of the website is listed below.