When Glossopteris Missed the Spring

Late in the Permian Period, springtime had clearly changed in what is now the Sydney Basin (New South Wales, Australia).  No longer did forests of Glossopteris trees greet the changing of the seasons with new leaves.  The collapse of this Glossopteris flora in the Basin’s ecology occurred some 370,000 years before the mass extinction of marine life on the planet which happened roughly 251.9 million years ago as part of the End-Permian-Extinction (EPE).  This is the picture that geologist Christopher R. Fielding and his colleagues paint in a new study drawing on careful study of geologic formations in the Sydney Basin that allow for fine tracking of changes in flora from the late Permian through the EPE, and into the first half of the Triassic.  (Fielding, et al., Age and Pattern of the Southern High-Latitude Continental End-Permian Extinction Constrained by Multiproxy Analysis, Nature Communications, January 23, 2019.)

The glossopterids were large, very likely deciduous gymnosperms with trunk diameters that could reach 80 centimeters (over 2.6 feet) and heights of up to 30 meters (over 98 feet).  They lived in water-soaked environments, creating “moderately dense mire forests.”  (For an excellent article on the Glossopteris, see Stephen McLoughlin’s Glossopteris – Insights Into the Architecture and Relationships of an Iconic Permian Gondwanan Plant, Journal of the Botanical Society of Bengal, 2011.)

Pictured below are my sole Glossopteris fossils - multiple impressions of Glossopteris sp. leaves stained red-orange with hematite (iron oxide) during the fossilizing process.  They stand out dramatically from the cream colored matrix of claystone, a sedimentary clastic (composed of rock fragments).  These were found near the town of Dunedoo in New South Wales, on the northwestern edge of the Sydney Basin.

The demise of glossopterids in the Sydney Basin was a change with probably profound implications for that location at that time,and possibly for us today.  In the Late Permian, the Glossopteris was under threat across the mid to high latitudes of the Southern Hemisphere.  Until then, these trees had been so abundant and widespread in the southern expanses of the world that paleontologists refer to the vegetation found fossilized in Permian alluvial settings of the Southern Hemisphere as “Glossopteris flora.”  Indeed, the Glossopteris is an index fossil used to identify Permian strata.

Fielding et al. attribute the demise of the glossopterids in the Basin to a relatively short period of climate change.  Temperatures rose.  As they put it, there was “a brief perturbation to warmer, more humid climate conditions.”  The largely complete disappearance of the Glossopteris in the Sydney Basin was a piece of a much more widespread vanishing of this plant across the southern latitudes prompted by subsequent changes in climate.  As paleontologist Stephen McLoughlin has written (see article cited above), “it is clear that the demise of the Glossopteris flora in most regions is intimately associated with the global environmental changes and biotic crisis at the close of the Permian.”  (p. 10)  The plant did not go extinct in the EPE, but, instead, hung on into the Triassic for awhile in the colder climates found in higher latitudes further south.

Significantly, Field et al. find no evidence in the Basin of an “exceptional erosional event or catastrophic physical degradation of the landscape” coincident with the EPE.  The damage to the glossopterids had been done hundreds of thousands of years earlier.

Geologist Robert A. Gastaldo, in an article that considers this work on the Sydney Basin, observes that Fielding et al. delineate a “scenario for how vegetation might respond to current global warming.”  (Ancient Plants Escaped the End-Permian Mass Extinction, Nature News and Views, March 1, 2019.  More on that title later.)  The experience of plants, such as the Glossopteris, so clearly sensitive to relatively small changes in the average temperature in the climate, “might be a harbinger of the plant group’s ultimate extinction.”  And it’s that related aspect of the research on this once amazingly abundant tree that intrigues and worries me.

It’s now very evident that spring is here in the Northeast United States, though for several weeks many subtle signs had been there to see.  In the 1930s, botanist and nature writer Donald Culross Peattie (1898 – 1964) noted in An Almanac for Moderns (1935) (written, I believe, when Peattie lived in the D.C. area and had a nature column in the Washington Star newspaper) that it was in the last week or so of March that one could say that spring had, in fact, arrived.  That was not too early, he thought, though “poets and musicians” tended to announce its coming in late April and early May when, he noted sarcastically, no fool could miss the signs.

Peattie wrote in his Almanac entry for March 24th:

So does our spring begin, in a slow flowering on the leafless wood of the bough of hazel and alder and poplar and willow, a hardy business, a spawning upon the air, like the spawning in the ponds, a flowering so primitive that it carries us back to ancient geologic times, when trees that are now fossils sowed the wind like these, their descendants – an epoch when the world, too, was in its naked springtime. (The Norton Book of Nature Writing, edited by Robert Finch and John Elder, 1990 p. 452.)

“Naked springtime” is a wonderful phrase for that very brief period when the woods are still airy and filled with myriad shafts of light, even as buds open and leaves unfurl.  Without the Glossopteris in the Sydney Basin, the nakedness was probably much more pronounced and long lasting.

Peattie’s observation for March 24th about the “spawning upon the air” describes a phenomenon with which we are very familiar, to wit, car windshields thickly coated in sticky yellow-green pollen.  But that pollen-based covering of cars is only just in its early stages here in the waning days of March.  Is this late for us?  Were we vigorously cleaning our windshields last year at this time or the year before?  I don’t remember, but I seriously doubt that spring typically arrived for Peattie earlier in the 1930s than it does for us today.

In fact, with the relentless climate change we’ve set in motion for the planet, spring is arriving earlier and earlier in many places.  Data from the citizen-science project, USA National Phenology Network, show that around the country, spring, or, at least, certain harbingers of spring have been arriving on average several days earlier in recent years compared to prior decades.  A recent study, based on USA-NPN data for the four major migratory bird flyways and for the National Wildlife Refuge System, finds that in those areas:

the onset of spring is now earlier in 76% of all wildlife refuges and extremely early (i.e., exceeding 95% of historical conditions) in 49% of refuges. . . .  This differential rate of advance in spring onset is most pronounced in the Atlantic flyway, presumably because of a “warming hole” in the southeastern US.  (Erik K. Waller, et al., Differential Changes in the Onset of Spring Across US National Wildlife Refuges and North American Migratory Bird Flyways, PLOS One, September 12, 2018, abstract.)

Some do argue that earlier plant growth in the early spring will lead to greater absorption by plants of carbon dioxide with an ameliorating impact on the warming climate, but recent research seriously challenges that contention, showing that early spring growth comes at a cost.  Water is absorbed from the soil earlier in the year and the plants are unable to sustain their growth spurt throughout the summer leading to increased drought conditions and early death of the plants.  Indeed, climate change modeling apparently assumes some degree of increased absorption of carbon dioxide which this research asserts is overestimated.  (See, for example, Marlene Cimons’ blog post titled With Shorter Winters, Plants Bloom Early and Die Young, National Geographic Blog, October 19, 2018.)

Earlier springs can have dire consequences for some species as dependent relationships that have built up over millennia are broken.  Mismatches between feeders and food sources are increasing.  For instance, research has shown that some migratory songbird species are arriving at their springtime destinations too late for their offspring to be sustained on caterpillars and other insects because those insects have long since emerged in order to feed on the plant leaves that have come out early.  Ecologist Stephen J. Mayor, as quoted in a Washington Post article on this research, observed, “The rate at which birds are falling out of sync with their environment is almost certainly unsustainable.”  He added, “We can end up with these increasingly quiet springs.”  (Ben Guarino, Experts Fear ‘Quiet Springs’ as Songbirds Can’t Keep Up With Climate Change, Washington Post, May 16, 2017.)

Peattie’s naked springtimes may become also very quiet springtimes.

I find it worrying that a dominant tree like the Glossopteris could be undone by relatively small increases in temperature in the Sydney Basin in the Late Permian, well before the severe changes in climate that marked the EPE elsewhere on the planet.  On point (and fueling my anxiety) is a recent study of the distribution today of 86 tree species in the Eastern U.S. that found that among important factors influencing the distribution of tree species, climate change had a significant (though not sole) impact, possibly driving some species northward to cooler climates and some species westward to areas of greater precipitation.  (Songlin Fei, et al., Divergence of Species Responses to Climate Change, Science Advances, May 17, 2017.)  Ecologist Fei and his colleagues, focusing on data covering a 30-year period that describe the geographical abundance of different tree species, found that 73 percent of the 86 species experienced a westward shift (mean shift per decade was 9.6 miles) and 62 percent of the 86 species moved poleward (per decade mean shift of 6.8 miles).  Clearly, some species moved both westward and poleward.  The angiosperms in the study group were more likely to more westward, most of the gymnosperms moved north (ah, there go the Glossopteris trees in the Late Permian).  The authors raised the possibility that this divergence might be related to the fact that most gymnosperms are pollinated by the wind, while angiosperms are pollinated by animals.  Nevertheless, trees are on the move today, a phenomenon with potentially profound affects.  Fei et al. write:

The reduction or replacement of certain species in a community can be consequential, because species can have substantially different effects on ecosystem structure, function, and services, and the impacts can cascade through a broad range of ecosystem processes.

Almost a no brainer to suggest that the interdependence of organisms in ecosystems means that the loss of any taxon (through extinction or movement to more hospitable environments) may have adverse consequences for other organisms in those systems.

As noted earlier, Robert Gastaldo's article has what would appear to be a rather contradictory title – Ancient Plants Escaped the End-Permian Mass Extinction – given its coverage of the research findings by Fielding et al. just described.  But Gastaldo reviewed not just Fielding’s work but also a study by Hendrik Nowak et al. of a database on the plant fossil record across the Permian-Triassic boundary.  Nowak and his colleagues found that the evidence of substantial plant extinction cross this boundary was largely a function of biases in the fossil record.  In fact, they found that diversity of plant genera was largely unchanged, even though species diversity declined in this period.  Gastaldo observes, “In contrast to prevailing wisdom, Nowak and colleagues demonstrate that land plants did not experience widespread extinction during Earth’s most severe biological crises.”  This finding, Gastaldo asserts, is supported by Fielding and his coauthors because they posit that, at the EPE, the environment in the Sydney Basin was not marked by any dramatic change or decimation of flora.

But I would caution that, though the analysis by Nowak and his colleagues does cast doubt on a significant extirpation of plants at the EPE, their work should not be read as evidence that all was well for plants at that point and that, more generally, plants have been able to skate largely unscathed through those events across deep time that decimate the ranks of marine organisms and land animals.  Changes in flora occur at these dramatic junctures in deep time, something that even Nowak et al. do acknowledge:

[T]he compositions of floras changed repeatedly throughout the history of land plants.  By all accounts, their dominance structures were also drastically altered during the Permian-Triassic transition both on the short term and long term.  (No Mass Extinction for Land Plants at the Permian-Triassic Transition, Nature Communications, 2019, p. 6.)

Further, Nowak and his colleagues observe that plants that rely in some fashion on the activities of animals are particularly susceptible during periods of mass extinction because animals are generally more at risk during periods of rapid environmental change.

Most troubling to me is the note of optimism (seemingly directed to those of us who worry about the impact of climate change) that Nowak et al. strike at the very end of their analysis for those plants that do not partner up with animals:

[O]ther major plant groups that rely on abiotic vectors have a comfortable chance of survival.  (p. 6)

Frankly, I found their conclusion puzzling and offering only cold comfort.  “Abiotic vectors” are those nonliving elements in the environment – light, temperature, atmospheric gases, pollution, geography, etc.  If the Glossopteris would be included in the abiotic plant groups then clearly there is something to worry about with changes in climate.  And, now revealing my ignorance and bias toward a belief that all living creatures are interdependent, I must ask, Are there really significant plant taxa reliant solely on abiotic vectors, that is, independent of any animal partners?

Even if there are, all other plants that clearly survive and flourish in partnership with animals are at risk and the consequences of the loss of such plants – think, for example, food crops – would be profound.  I conclude that, whether or not plants generally managed to make a transition across the Permian-Triassic boundary without the same level of extinction that marine organisms or land animals experienced, the earlier blinking out of Glossopteris in the Sydney Basin means something troubling for us today in this 2019 springtime.

Patrick Principle(s)

My father “influenced me to realize that the most important things in life [are] to understand the natural world and . . . to be kind to my fellow man, even though I might not understand them.”
   ~ Ruth Patrick, Hometown Legends:  Ruth Patrick, WHYY TV, aired October 30, 2004

 Perhaps I’m impressed by trivial connections that I consider insights and the one at the center of this post might be one of those.  Even if that’s true, Ruth Patrick is someone we should all get to know.

Over the past several weeks, I have been reading a couple of informative and entertaining accounts of the Permian extinction, that mother of all mass extinctions – Gorgon:  Paleontology, Obsession, and the Greatest Catastrophe in Earth’s History by Peter D. Ward (2004) and Extinction:  How Life on Earth Nearly Ended 250 Million Years Ago by Douglas H. Erwin (2006).  Ward and Erwin, both practicing paleontologists, certainly know how to write for a popular audience.  Ward’s account focuses on terrestrial extinction, particularly as it is recorded in the bleak and beautiful Karoo region in South Africa.  His is a decidedly more personal story (sometimes too much so) as he plays the starring role; on occasion, it crosses into the “tell all” territory (one wonders whether he has been able to continue to work with at least one of his colleagues, Roger Smith, after the way Smith is characterized in the book).  Erwin’s volume offers a more deliberate explanation of the Permian extinction and a well-structured exploration of the various hypotheses about its causes.  It, too, ventures into the first person at times when it takes the reader into the field.  Good videos of talks on this subject delivered by both authors are available on the web.  There’s Ward’s TED talk and Erwin’s talk at the Santa Fe Institute.

I found one aspect of the aftermath of the Permian mass extinction that both Ward and Erwin describe to be particularly surprising.  Yes, the Permian extinction cut a devastating swathe through the ranks of plant and animal taxa.  For example, according to Erwin, the two pulses of Permian extinction, separated by some 10 million years, eliminated at least 90 percent of all marine species.  I suppose I’d previously assumed (if I'd actually had any coherent thoughts about it) that a devastated, lifeless environment ensued and endured for thousands, hundred of thousands, or perhaps millions of years.  But that’s not necessarily the case.

Erwin opens his book in Utah, where “the Triassic is laid out for anyone who cares to look, although few do,” apparently because the fossils are either scarce or boringly the same.  (p. 1)  Later, he describes formations that were laid down during the early stages of recovery from the Permian extinction, formations that essentially are “pavements built of thousands upon thousands of specimens of the characteristic Early Triassic scallop Claraia. . . . Despite the incredible abundance of some species, the total number of Early Triassic species is a tiny fraction of those alive only a few million years earlier or later.”  (p. 200-221)

Along the same lines is this observation by Peter Ward about fossil hunting in the Karoo,

For reasons still unfathomable, the lowest Triassic strata above the mass-extinction boundary are composed of red beds packed with fossils.  Almost all belong to a single species of mammal-like reptile – Lystrosaurus.  After the hard work of finding the very rare fossils in the youngest Permian beds, the fossils in these oldest Triassic beds were indeed a holiday.  There is an irony and mystery to this.  These beds were deposited soon after the mass extinction.  Yet the fossils – at least of this one species – are very common.  (p. 145)

(The fossil skeleton of the pig-sized Lystrosaurus hedini is shown above in a photograph by Rama, downloaded from Wikimedia and reproduced under the Creative Commons Attribution-Share Alike 2.0 France license.)

Ward suggests that perhaps this simply reflects that, in the post extinction period, conditions conducive to fossil formation were more prevalent.  But, significantly, he adds, “Or perhaps there were more animals – at least of this one single species.”  (p. 145)

In the midst of my immersion in the Permian extinction and its consequences, I happened to come across obituaries for botanist and ecologist Ruth Patrick (1907 – 2013), who died on September 23, 2013 (Julie Zausmer, Ruth Patrick, Ecology Pioneer, Dies at 105, The Washington Post, September 23, 2013; William Dicke, Ruth Patrick, a Pioneer in Science and Pollution Control Efforts, is Dead at 105, The New York Times, September 23, 2013.)

What a marvelous human being she was.  I am quite taken by her life story and scientific endeavors for many reasons.  One of them is the link, at least I think it’s a link or a connecting insight between Patrick’s signal contribution to science – the so-called Patrick Principle – and the aspect of the aftermath of the Permian mass extinction that I’ve just described – loss of taxonomic diversity.  In addition, a side of her life that I found particularly compelling was her relationship with her father.  I consider both of these topics below.

(This picture of Ruth Patrick is reproduced with the permission of the Ruth Patrick Science Education Center at The University of South Carolina Aiken.)

Patrick was a pioneer in many ways, not only as a woman breaking into the male-dominated scientific ranks in the 1930s and 1940s (talk about surviving in a hostile environment), but also as a botanist central to the modern development of the science of limnology (study of the ecology of rivers).

In 1934, largely because she was a woman and the Depression was in full swing, Patrick who was about to earn her doctorate from the University of Virginia could only find volunteer work at the Academy of Natural Sciences in Philadelphia.  In recounting her work experiences in science and at the Academy, Patrick was very matter of fact about the sex discrimination she encountered.  Not until 1945 did the Academy begin to pay her a salary.  In time, she established a department of limnology in the Academy, taught for many years at the University of Pennsylvania, published over 200 articles and several books, was elected to the National Academy of Sciences, and received the National Medal of Science, as well as the John and Alice Tyler Ecology Award.

She was a force to be reckoned with.  Her husband, entomologist Charles Hodge, once described his marriage as “like being married to the tail of a comet.”  It is clear in the 2004 WHYY TV show devoted to Patrick that, even at age 96, she remained youthfully passionate about science and about the role of women in the sciences.

Her key scientific contributions came from her study of diatoms (single celled algae), particularly her analysis of the relationship between water quality and the diversity of diatom communities in rivers.

(Photo on left is of Amphiprora alata (95 microns or 0.095 mm long); on right is Achnanthes frigida (no length given).  These images are from the Smithsonian Environmental Research Center's Phytoplankton Guide to the Chesapeake Bay and Other Regions.  They are used with permission of the Smithsonian.)

I do not pretend to know Patrick's work, reliant as I largely am on others’ descriptions, but it is widely asserted that Patrick was instrumental in a major shift in how water quality is analyzed, broadening it from a narrow focus on the presence of pollutants in the water to an appraisal of the diversity of the communities of organisms living in the water.  Her work on water pollution helped lead to enactment of the Clean Water Act.

Her conclusion that the diversity of species living within a fluvial environment reflects the overall health of this water is sufficiently profound that biologist Thomas E. Lovejoy has named it the Patrick Principle.  He writes,

In 1948 a line of research led by Ruth Patrick on freshwater communities in the United States (principally rivers) demonstrated that the number and variety of species reflected the natural physics and chemistry of a river as well as the stresses to which it was subject (e.g., pollution).  This work, which deserves to be recognised as the Patrick Principle, can be generalized to all kinds of biological communities, i.e., marine and terrestrial as well as freshwater.

Put differently, environmental stresses are all defined as problems because they affect living systems (not just humans).  So whether pollution, habitat destruction or climate change, they all impinge on biological diversity.  Consequently biological diversity is the ultimate integrator of environment change.  When that change is sufficiently intensive and extensive it leads to species extinction.  That, together with the scale and rate of the various kinds of environment change, conspires to create the biological diversity crisis.  (Biodiversity:  Threats and Challenges, in Biodiversity, Sustainability and Human Communities:  Protecting Beyond the Protected, edited by Tim O’Riordan and Susanne Stoll-Kleemann, 2002, p. 34. )

If I interpret the Patrick Principle properly, it’s that in times of environmental stress the diversity of the species that remain within the community is changed and impoverished.  Indeed, it’s possible that some of those that survive the stresses actually thrive.  Perhaps in the three decades since we were first introduced to the terms biological diversity and biodiversity we’ve become so familiar with them and their implications for our understanding of the environment that the Patrick Principle seems like a truism.  It shouldn’t be.

And then, at some point, I made what probably seems to be the pretty obvious connection between the aftermath of the Permian extinction and the Patrick Principle.  The consequences of environmental degradation documented in American rivers and streams by Patrick (the lessened diversity of life, not necessarily its absence) played out in the lowest Triassic – fewer species but, in some places, an abundance of individuals, like the Early Triassic scallop Claraia or the herbivore Lystrosaurus hedini.

Maybe it’s a prosaic insight, but it’s what I had.

There’s another aspect of Patrick’s life that I found particularly appealing – her unbridled admiration of her father.  (I suppose as a father, I’m inclined to make a big deal out of this.)  Her father, a lawyer, not only instilled a love of nature in Ruth and her sister, but also encouraged them to reject the traditional roles that females were expected to play in society, much to consternation of his wife.

Ruth recounted that her father “loved the natural world.”  (This and all subsequent quotations are from the WHYY show Hometown Legends:  Ruth Patrick cited earlier.)

Every Sunday afternoon, from the time I was five to about twelve, I would take a walk with him.  And we would always go to some woods.  Typically I would carry a basket.  And when I was little, of course I collected everything, worms, mushrooms, plants, and rocks, and everything and then we’d go home.  And my sister and I would have our milk and crackers, and, while we were eating and afterwards, Father would identify what we had in our baskets.  And, of course, we felt very proud if we could identify them and tell him what they were.

That her scientific pursuits had her mucking around in fields and streams did not sit well with her mother.  Even as her mother “felt girls should be in the home, not out in the fields, so to speak,” Patrick turned to her father and followed his advice, embracing science, academic pursuits, and the field.  In that day and age, she noted, “Ordinarily, [a] nice, healthy girl, just shouldn’t want to get a Ph.D.”  But, her father “believed that women could accomplish a good deal.  He used to say to me, ‘With your spare time, read, improve your mind.  You can hire people to wash dishes.’”

And, so, into her old age, Ruth Patrick remained focused on “trying to understand the natural world and to understand why we have the assortment of species we do have operating in our ecosystems and how can we protect them, how can we keep it happening.”

Classical Gas

In which the blogger ponders breaking wind, benefits of a toxic gas, mass extinctions (ah, the paleontological link), and taking blood pressure in mice – yes, the usual mélange.


A Passing Gas

Pediatrician Howard Bennett contributes a column to the kids’ page of the Washington Post and his little identifying blurb at the bottom of each column says that “he writes about gross things” – very true. His columns are direct, informative, fun, and never condescending to his (supposed) young audience. A quintessential example is the column that ran on February 22, 2010, with the daring title (daring for the Post and, yes, it generated complaints) of :

“Ever Wondered Why People Fart?”

Thank you for asking. Yes, I have.

According to Bennett, it’s a combination of the air we swallow (some of which reemerges as belches – topic of his previous month’s column, of course) and the job done on undigested food by the bacteria that inhabit our gut. These bacteria add gases, including oxygen, nitrogen, hydrogen, carbon dioxide, methane, and hydrogen sulfide, to the swallowed air and that gaseous mixture has to get out some how.

As for that smell, credit goes to the hydrogen sulfide some of the bacteria produce as their own waste product from chowing down. Hydrogen sulfide (H₂S) – that’s the paleontological link here. More on that in a moment.

I’m still lingering on the flatulence and the smell. Biologist Betsey Dexter Dyer knows bacteria and she wants us to know them, too. In her book, A Field Guide to Bacteria (2003), Dyer identifies the macroscopic field marks of bacteria, those signs around us of the presence of different species of bacteria that we can see (without a microscope), smell, taste (think I’ll pass), and touch. As for the bacteria in our intestinal tract, it’s not surprising they’re there, because, as Dyer writes, “Guts are safe, nutrient-rich places, extremely popular as habitats . . . .” (p. 16-17) The gut-dwelling bacteria work at fermenting and processing food our own enzymes cannot. Dyer ascribes the smell of flatulence to sulfate-reducing bacteria, and some fermenter bacteria, particularly when they process foods with abundant sulfur compounds (e.g., broccoli). These sulfate-reducing bacteria in our gut produce hydrogen sulfide as a waste product.

But, wait, isn’t hydrogen sulfide, even in relatively slight concentrations, highly toxic? Yup, it kills. Farting, clearly, is no joking matter.

“Yet, paradoxically, we need H₂S to survive,” asserts biologist Rui Wang in a recent Scientific American article on the positive and potentially lifesaving attributes of hydrogen sulfide. His primary focus is not on the gas being generated in our intestines, but rather on that produced by the human body in blood vessels. (Toxic Gas, Lifesaver, by Rui Wang, Scientific American, March 2010) It turns out that an enzyme found in blood vessels combines with a specific amino acid to produce hydrogen sulfide, among other compounds. Working with rats, Wang found that H₂S helps to regulate blood pressure by causing smooth muscle cells to relax, thereby dilating blood vessels. (The effects of another gas, nitric oxide, on reducing blood pressure are well established.) Wang notes that the potentially positive reach of hydrogen sulfide in the human body may extend beyond the cardiovascular system; it may have positive effects in the nervous system. Regulation of metabolism may also be one of its effects, leading Wang to some dramatic speculation about hydrogen sulfide hibernation to stabilize trauma victims at disaster sites. Pretty heady stuff.

Smelly Extinctions – An Upside?

So, a little hydrogen sulfide, good; more, bad. Each instance of hydrogen sulfide production in the human body appears to have an upside, despite the toxicity of the compound. Wang suggests that this capacity of humans to utilize hydrogen sulfide has its roots in our long, long, long ago ancestors’ survival of the massive Permian extinction. The theory of the causes of this extinction, described by Wang, features enormous amounts of hydrogen sulfide generated by bacteria thriving in oxygen-depleted oceans. When that gas, so the theory goes, bubbled to the surface of the ocean, it made the atmosphere toxic. Wang writes:

The importance of H₂S in human physiological processes is probably a holdover from that long-ago time. The creatures that survived this catastrophe were the ones able to tolerate and, in certain cases, even consume hydrogen sulfide, and we humans have retained some of that affinity for the gas.

If true, I wonder if our tolerance for hydrogen sulfide produced by sulfate-reducing bacteria in our intestines is another legacy of that survival.

With regard to the Permian extinction and hydrogen sulfide, Wang cites an article by paleontologist Peter D. Ward (Impact from the Deep, Scientific American, October, 2006). To say that Ward is prolific is a gross understatement. He’s written many informative and entertaining books on this and related topics, and there are various videos out there of him lecturing on these issues, including a succinct and amusing one posted on dotSub from about a year ago.

Ward, as I understand him, posits that possibly only the extinction at the end of the Cretaceous was the direct outcome of an impact with Earth of a large extraterrestrial object. He labels others, such as the Permian and the one marking the divide between the Triassic and Jurassic, as “greenhouse extinctions” and a central villain in each is hydrogen sulfide. Ward asserts that the greenhouse extinctions follow a generally similar sequence of steps (a few are cited in this post – for more detail, see Under A Green Sky (2007), particularly p. 137-138): temperatures on the planet rise relatively suddenly due to the release of carbon dioxide and methane from vast areas of volcanic action called blood basalts; the warming of the world changes ocean circulation patterns leading to a growing presence of warm low-oxygen water at the ocean bottom; over time, this anoxic water pushes up toward the top, reaching sunlight which sparks massive growth of bacteria in this water that produce hydrogen sulfide in enormous quantities; this gas bubbles from the ocean into the atmosphere killing some life as it goes and subsequently destroys the ozone layer, delivering the coup de grâce.

Now, that’s what my family, invariably in a conversation around the dinner table, would certainly call “TF” or terminal flatulence.



Postscript – Working with Mice

To refine his research further, Wang and others developed a line of mice lacking the enzyme that enables production of hydrogen sulfide in blood vessels. They analyzed the impact on blood pressure of the absence of this compound in these mice and then its reintroduction.

So, how is blood pressure measured in mice?

With little blood pressure cuffs, attached to their tails.

Not sure I’d trust those readings. Surely, a lab mouse’s blood pressure must soar as a lab worker approaches with the little blood pressure cuff (“oh, no, not the tail again”) – yes, a classic case of “white coat hypertension.”