Dmitri Sobolev's model of mass extinction

Dmitri N. Sobolev (1872–1949; Fig. 1) was a fairly noted Russian geologist and paleontologist, best known today as an unsuccessful propagator of the non-Darwinian saltational model of phylogeny and a “heretic” ammonoid taxonomy (Kolchinskiy 2002; Dzik 2003; Popov 2008). Although Russian, his scientific career, as a graduate of the University of Warsaw, was inextricably linked to today's Poland and Ukraine. Sobolev made a major contribution to our understanding of the Paleozoic and Quaternary geology of Poland, and beginning in 1914, he continued his scientific activities at the University of Kharkov, working on tectonics, geomorphology, and mineral resources of the western Soviet Union (Racki 1979; Ozonkowa 1980; Dzik 2003; Solovyev et al. 2014; see also  http://geologia.univer.kharkov.ua/index.php/about-us/vidatni-spivrobitniki).

During the years 1926–1928, Sobolev published in Kiev a three-part, in-depth treatise entitled Zyemlya i zhizn, also outlined in two popular-science articles in Priroda (Sobolev 1915, 1927). In the third part, he discussed the issues related to the causes of organisms' extinction and recognized several Phanerozoic mass extinctions; four of these great biotic crises are accepted today: the end Ordovician, Late Devonian, end Triassic, and end Cretaceous. Sobolev put forward a theory of cyclic (diastrophism-related) volcanic cataclysm as the main trigger of these biotic revolutions. He stated (1928: 74): “The environment is persistently and continuously formed and converted by the life and other terrestrial forces, in harmony with diastrophism in their activity. These large-scale paroxysms, which accelerate the beating pulse of the Earth and increase the energy of the breath of the Earth, radically reconstruct and renew both the land and the sea bottom, change properties and composition of the atmosphere, hydrosphere and stratosphere, with which is connected terrestrial life. Disturbing the balance of life setting, they oscillate the equilibrium between the Earth and life and the equilibrium in life itself (…)”.

Sobolev recognized the perturbation in the dynamic equilibrium of gaseous exchange between the atmosphere and biosphere, i.e., carbon dioxide/oxygen imbalance, as a direct effect of increased volcanic emission of CO₂ (probably also H₂O, H₂S, and NH₄). As an ultimate killing factor for animals, he considered “oxygen starvation”, in effect a massive oxygenation of injected volcanic gases that removed atmospheric oxygen, but also “carbon dioxide starvation”, owing to large-scale CO₂ storage in carbonate and coal deposits. Thus, Sobolev finally proposed a prolonged, stepwise biotic crisis scenario in both animal and plant kingdoms during the orogenic cycle, with feedbacks that feature prominently in modern-day extinction scenarios. The lethal feedbacks include, among others, pH changes (and crucial ion ratios, such as Na+K to Ca+Mg) and anoxia in marine settings, and a cascade effect in the trophic pyramid after vegetation demise. Considering the physiologic and biogeochemical aspects of his thinking, Sobolev was mainly guided by the observations of the American biologist, Jacques Loeb (i.e., a kind of actualistic conceptual foundation), and the Gaia-like model of Vladimir I. Vernadsky (e.g., Loeb 1916; Vernadsky 1926). Thus, Sobolev struggled with uniformitarianism using actualistic arguments. The Lilliput effect and extinction selectivity were announced in his papers, as well as augmented chemical weathering in a CO₂-enriched moist atmosphere, resulting in the enhanced input of Ca and Mg from land to sea. In the crucial climatic context, Sobolev ruled out cooling as a mechanism (e.g., Schuchert 1914), instead stressing, following Loeb's experiment results, increased animal mortality with increased temperature. In consequence, he suggested volcanically- induced warming in CO₂ enriched atmospheres along lines similar to the volcanic summer scenario (see review in Bond and Wignall 2014).

Fig. 1.

Dmitri Nikolayevich Sobolev as the Professor of Geology at the University of Kharkov (photo courtesy of the University of Kharkov).

Other Russian pioneers of volcanic Catastrophism

An overall analogous concept of the volcanic catastrophe at the end of the Cretaceous (K–T boundary), an alternative to the bolide impact cataclysm, is usually thought as founded in the pioneering work of American geologists, such as McLean (1985), although the preceding less known South African contribution by Oelofsen (1978) is noteworthy. McLean (1985: 235) summarized the K–T scenario thus: “gradual (…) bioevolutionary turnover during a period of disequilibrium between the rate of mantle CO₂ degassing and uptake by sinks”, in harmony with Sobolev's (1927, 1928) paradigm. On the other hand, the hypothesis of fatal volcanic eruptions in the Deccan peninsula was actually proposed in 1924 by the Professor of Geology and Paleontology at the University of Moscow, Aleksey P. Pavlov (1854–1929), and similar K–T boundary “ridiculous notions” were at that time published also in Poland (Łoziński 1927) and USA (Marshall 1928; see also Müller 1928). Sobolev himself underlined the inspiring importance of the geological revolutions predicted by Pavlov (1924), who first proposed the possibility of ecosystem devastation by volcanogenic acidification (HCl and H2SO4). Furthermore, he clearly recognized a magmatic trigger of the end-Permian mass extinction, unexpectedly undervalued by Sobolev. Pavlov (1924: 97) mentioned even the Siberian traps, although due to the imprecise dating of these flood basalts, he did not make a causal link between their emplacement and any biotic crises.

A similar model of non-actualistic worldwide cataclysm, initiated by trap-type volcanic activity, was first discussed in 1916 in the popular-science article, entitled “Catastrophes in Earth History”, by Mikhail A. Usov (1883–1939), a young Siberian geologist from Tomsk University. Unlike his contemporaries, Usov entertained notions of an extraterrestrial trigger for some biotic crises, guided by the only the incipiently known meteorite crater in Arizona! He illustriously introduced his main approach in these words: “(…) much exists reasons for assuming that between the history of the Earth and the life of individual representatives of the organic world exists a significant analogy. And, if in the lives of the organisms, which are developed gradually, there are manifested occasionally of shocks of diverse kind, then is possible to expect, that also the Earth, calm generally on the people memory, it was not always the same; that occurred sometimes a rapid and pronounced change on the surface or in its depths, (…) that they would generate on us, so adapted to see entire that surrounding in seemingly solidified forms and to step confidently on the firm ground, the terrible impression of catastrophes” (Usov 1916: 437).

Final remarks

It is surprising that even such a multi-language erudite as Sobolev did not know (or ignored?) several benchmark papers that considered themes similar to his own. The greenhouse effect of volcanogenic CO₂ was conspicuously highlighted by the famous Swedish chemist Svante Arrhenius already in 1896. Regarding this stimulus in the global carbon cycle, Arrhenius stressed significance of another Swedish mineralogist and geologist, Arvid G. Högbom (Högbom 1894). Again, if truth be told, this credit in carbon cycle matters should be referred to the French visionary geochemist (in a recent sense), Jacques J. Ėbelmen (1845, 1847), as revealed by Berner and Maasch (1996). Ėbelmen (1847: 652) surprisingly hypothesised that the biosphere could collapse as a consequence of total volcanic quiescence that eventually led to a CO₂ deficiency due to chemical weathering. However, the concept of fluctuating atmosphere composition in geological history, as a major control of biotic evolution, may be traced many decades earlier, because it was delineated by the pre-Darwinian Scottish evolutionist and horticulturalist Patrick Matthew in 1831 (see Rampino 2011). Matthew (1831: 382) rationally deduced: “When we view the immense calcareous and bituminous formations, principally from the waters and atmosphere, and consider the oxidations and depositions which have taken place, either gradually, or during some of great convulsions, it appears at least probable that the liquid elements containing life have varied considerably at different times in composition and weight; that our atmosphere has contained a much greater proportion of carbonic acid or oxygen and that our waters aided by excess carbonic acid, and greater heat resulting from greater density of atmosphere, have contained a greater quantity of lime and other mineral solutions”.

In the last years of his life, Sobolev summarized his scientific career with a frustration: “What of [my] works is overall accepted, it does not present the scientific merit, but what I consider to be the most important, this is not acknowledged by others or indeed is rejected” (quoted from an unpublished manuscript dated 1943; Ozonkowa 1980: 140). His cyclic concept of Earth history was even criticized in 1935 from a “dialectic” viewpoint (see reply in Sobolev 1935). In fact, Sobolev and other creative Russian scholars were truly conceptual forerunners of the global catastrophe model in Earth history which is now widely accepted as the volcanic/greenhouse scenario, in particular for the end-Permian ecosystem collapse (Bond and Wignall 2014).

These progressive ideas of “crazy catastrophists” were evidently overlooked in mainstream science and forgotten for many generations (although see Hoffman 1989 for an exception). Kolchinskiy (2002: 306) remarked: “Now, when the publications, scoped on the possibility of sudden speciation and global turnovers by some planetary factors of cosmic (asteroid explosion, collision with a comet, supernova blast) or terrestrial origin (volcanism, orogenesis, transgression), they are calculated by the thousands, it is appropriate to recall name D.N. Sobolev”. Therefore, the nearly unacknowledged intellectual contribution of many European countries in developing ideas on mass extinction science, highlighted herein, significantly predate the North American renaissance in this field over the past 30 years.