Perspective Chapter: Plate Tectonics and Global Dynamics of Biodiversity

Abstract

The article analyses the relationship between tectonic plate movements and global biodiversity dynamics. A new tectonic hypothesis of the causes of mass extinctions of biological species, which have repeatedly occurred in the history of the biosphere, is considered. It is proposed that the triggering mechanism for such extinctions is the periodic unification of lithospheric plates, leading to the formation of supercontinents and, consequently, to a decrease in the geographical isolation of species, increased interspecific competition, climate change, a decrease in the shelf area, changes in global sea level, and other determinants of biodiversity. The separation of lithospheric plates increases the degree of geographic isolation and, conversely, causes a new burst of species diversity that is greater than the previous one, as it engages the species best suited to the changing environment and wins the competition. The tectonic factor (geodynamics) thus becomes an important factor in the dynamics of biodiversity and evolution in general. Similarly, the dynamics of biodiversity are affected by contemporary processes of globalization: the human-accelerated reduction of habitats for native species, the removal of the factor of geographic isolation due to introduction, and increasing invasions are also leading to another mass extinction.

1. Introduction

Elucidating the causes and mechanisms of mass extinctions of species, which have repeatedly occurred over more than 4 billion years of the biosphere’s history, is one of the most interesting unresolved issues in the evolution of life on Earth. The number of species inhabiting the biosphere periodically dramatically decreased against the background of a general growth trend. There are more than a dozen hypotheses to explain this, which consider phenomena of a very different nature as the main cause, namely: cosmic catastrophes (first of all, the fall of large meteorites, other phenomena of cosmic origin); supervolcano eruptions; trap magmatism; climate changes (glacial cycles or even temperature increases critical for certain species [1]); changes in the level of the World Ocean; changes in the chemistry of the atmosphere and oceans (including changes in the atmospheric oxygen level); changes in Earth’s magnetic field (periodic exchange of the south and north poles [2]); genetic problems (in particular, genetic diversity loss, diseases, such as osteoporosis in extinct mammoths [3]); and even the anthropogenic factor, despite its “biospheric youth.” However, none of these hypotheses is universal; each one explains, as a rule, only one of the extinctions, considering coincidence in time only.

It should also be noted that the events considered as the root cause of mass extinctions occur much more often than mass extinctions themselves, and for some reason, their other manifestations are not associated with mass extinctions. For example, the death of dinosaurs at the border of the Mesozoic and Cenozoic is associated with the formation of one of the largest impact craters (astroblems) on Earth – Chiksulup – with a diameter of about 180 km on the Yucatan Peninsula. At the same time, the formation of a number of craters much larger than Chicksulup in size (namely, Warburten in Australia – 400 km, Vredefort in South Africa – 300 km, Sadbury in Canada – 250 km, and Dowling in China – 190 km) was not accompanied by subsequent extinctions and even global climatic changes, although they significantly exceeded the Yucatan event in terms of impact.

In our opinion, since mass extinctions have taken place in the history of the biosphere repeatedly, even with some regularity and in the same way, there must be one reason that prompts these biospheric crises.

2. Global dynamics of biodiversity

Table 1 summarizes information about the most famous mass extinctions according to the literature data with their supposed root cause.

Major mass extinction (Size of the extinction)	When (million years ago, Mya)	Supposed causes of mass extinctions
The Ordovician-Silurian extinction mass extinction (~ 85% of all living species eliminated)	The Paleozoic Era, End-Ordovician (~ 440–445 Mya)	Beginning of glacial cycles on Earth, and corresponding changes in sea level; Changes in atmospheric and oceanic chemistry relating to the rise of the Appalachian mountains.
The Late Devonian mass extinction (~ 80% of all living species eliminated)	The Paleozoic Era, End-Devonian (~ 383–359 Mya)	Climate change, possibly linked to the diversification of land plants; Decrease in oxygen levels in the deep ocean.
The Permian mass extinction (~ 96% of all living species eliminated)	The Paleozoic Era, End-Permian (~ 250–252 Mya)	Volcanic activity; Climate change; Decrease in oxygen levels in the deep ocean; Changes in atmospheric chemistry; Changes oceanic chemistry and circulation.
The Triassic-Jurassic mass extinction (~ 50% of all living species eliminated)	The Mesozoic Era, End-Triassic (~ 200 Mya)	Volcanic activity
The Cretaceous-Paleogene (K-T) mass extinction (~75% of all living species eliminated)	The Mesozoic Era, End-Cretaceous (~ 66 Mya)	Asteroid impact; Volcanic activity; Climate change; Changes in atmospheric and oceanic chemistry.

Table 1.

Major mass extinction and geodynamic situation (by [4, 5]).

Why, for what, and how do extinctions occur? There are still no unambiguous answers to these basic questions, which arise in the analysis of biodiversity dynamics.

The extinction of species as a result of natural processes is a normal phenomenon, balanced in geological time by the appearance of new species. According to C. Darwin [6], the extinction of species and their entire groups, which played such an outstanding role in the organic world history, is an almost inevitable consequence of the principle of natural selection. According to V.A. Krassilov [7], extinction is a way of regulating diversity under variable conditions, which weakens competition.

From the evolutionary viewpoint, the cause for the extinction of species is considered to be their permanent improvement in order to maximize the use of the environmental resources, which, in turn, is changed by new species in their favor. In the biosphere evolution process, the number of species increased, the biosphere spread to areas unoccupied by life, included new substances in the orbit of its activity, and utilized the energy of sunlight and chemical compounds more and more efficiently. Academician M.A. Fedonkin [8] noted: “extinctions were a boon for the biosphere, just as the death of an individual from old age is a boon for the species. In both cases, the carriers of inert hereditary information, which hinders evolution are cut off.”

In the evolution process of the biosphere, the number of species was continuously increasing: from the Cambrian to the Silurian, over 200 million years, the number of families of marine animals increased from 5 up to 400. By the Quaternary period, the number of families of marine animals alone increased to 750. At the same time, the dynamics of biodiversity, as well as the evolutionary process as a whole, was of a spasmodic nature: there were several large bursts of speciation and extinction, when entire families, orders, and even types of organisms appeared or disappeared. Several mass extinctions have been identified over the past 500 million years. The most famous, although not the largest, Cretaceous-Paleogene extinction (~65 million years ago) took away more than half of the species, including dinosaurs. During the period of the “great” Permian extinction (~250 million years ago), according to some estimates, ~90% of the species became extinct.

In the period accessible to the paleontological record, five mass extinctions are identified, as a rule; they are viewed in Figure 1 and listed in Table 1. J.D. Corso et al. [10] proposed to add the extinction in the Carnian pluvial period (~233 Ma ago) to them as a sixth one. Ceballos et al. [11] proposed to consider the modern period associated with human activity as the sixth mass extinction.

Figure 1.

Changes in the diversity of marine animals: A – Orders, b – Families, c – Genera. N is the number of taxa that existed at the lower boundary of the century, and N_R is the number of modern taxa known in the fossil state [9].

3. Features of mass extinctions

An analysis of the nature of mass extinctions allows us to note some of their characteristic features, namely:

1. after a sharp decrease in the diversity of biological species during their death, at the next stage of evolution, biodiversity was restored and subsequently exceeded the precrisis level;

2. the duration of mass extinctions is sometimes estimated as millions of years (the Late Devonian extinction, according to Racki et al. [12], lasted ~13 million years), which does not correspond to the duration of catastrophic events and their consequences (as a rule, few years);

3. mass extinctions concerned various animal species to a much greater extent than plants, which cannot be explained within the framework of the existing, especially catastrophic, theories; and

4. most of the events indicated as the causes of mass extinctions for some reason acted as such only once, although they occurred regularly. For example, giant eruptions of supervolcanoes occurred quite regularly. For example, the Yellowstone supervolcano erupted relatively often: 640 thousand years, 1.3 and 2.1 million years ago.

Since mass extinctions have been repeated more than once in the history of the biosphere, there must be one root cause to prompt global fluctuations in the numbers of species.

Without downplaying the role of catastrophic events in the decline in the abundance of many biological species, let us try to look at mass extinctions from an evolutionary position, taking into account the horizontal and vertical movements of lithospheric plates. These movements lead to the consolidation and separation of continents, islands, and, accordingly, to changes in the geographical isolation of biological species. Some considerations in this regard were expressed by us earlier [13, 14]. A possible relationship between tectonics and the mass extinction was discussed in refs. [15, 16] when the formation of the Pangea supercontinent most obviously coincided with the largest Permian-Triassic extinction. At the same time, a somewhat belated extinction effect was noted.

4. Consolidation of lithospheric plates as the root cause of mass extinctions

The development of life on our planet over the billions of years of the biosphere’s existence was under the continuous influence of geological processes, both catastrophic (volcanism, earthquakes, etc.) and much slower, but permanent in their manifestation, such as horizontal and vertical movements of Earth’s crust. Such movements cause changes in climate, orography, and length of coastlines as well as changes in other environmental conditions, including the isolation factor of biological species.

As the main universal root cause of mass extinctions, we propose to consider relatively slow movements of lithospheric plates, due to which, periodic consolidations and separations of continents and islands occur and large continental associations are formed up to a single supercontinent such as Pangea (Figure 2), Gondwana, Rodinia, etc.

Figure 2.

The late Paleozoic supercontinent Pangea as envisioned by Wegener (1922) (from [17, 18]).

With this, the movements of lithospheric plates significantly change the isolation factor, which plays a very important role in speciation. Populations of species turn out to be either united over vast expanses or disunited on separate continents and islands.

It is important to note that the periodic consolidation and divergence of lithospheric plates had a regular character. Figure 3 illustrates the periodic merging of lithospheric plates to form the supercontinents Pangaea, Gondwana, Rodinia, Columbia, etc.

Figure 3.

Evidence of the association of lithospheric plates based on the comparison of orogenic peaks (arrows) recognized on radiometric data with spectra of U – Pb detrital zircon crystallization ages and proposed times of supercontinent assembly [19, 20].

Further movement of lithospheric plates, according to the hypothesis of the American geologist Ch. Scotese [21], will lead to the formation of a new single supercontinent Pangaea Ultima in 200–300 million years when the British Isles will turn to be in the North Pole region, while Alaska and Siberia will move to the subtropics. Other versions of the next supercontinent are also being considered: the Novopangea, Amasia, Pangea Proxima, and Aurica [16].

Ecological consequences of the consolidation of lithospheric plates. In an ecological sense, the consolidation of lithospheric plates leads to the removal of geographical barriers and a decrease in the factor of geographic isolation of species.

When the continents unite, not only do the climatic and geomorphological¹ conditions change but also several species belonging to the same ecological niche in the united spaces may well merge. As a result, interspecific competition increases, and the competitive exclusion rule² comes into play.

According to this rule, two or more species cannot coexist stably within a limited space if they occupy the same ecological niche. The process of competition in this case always proceeds until the complete displacement of one species by another. Species less adapted to environmental conditions die out.

Another important consequence of the unification of continents is the reduction in the number of ecological niches due to the decrease in the diversity of climate and other geographical conditions, which also reduces the opportunities for the existence of species. At the same time, the length of coastlines is reduced and the area of life-rich shelf ecosystems is sharply reduced.

Consequently, the consolidation of lithospheric plates, due to the amalgamation of species in similar ecological niches and the decrease in their diversity, triggers the mechanism of interspecific competition. In the further process of extinction of species, a variety of factors become important, namely: physiological characteristics, the degree of adaptation to food resources, and changed climatic and other geographical features.

For example, presumably, when six continental plates are combined, up to six different species could appear within one ecological niche, five of which are evolutionarily doomed to slow extinction due to strong interspecific competition. Perhaps that is why the most massive was the Permian extinction 250–252 Ma ago, which claimed up to 90% of species and was timed to coincide with the unification of most lithospheric plates into a single supercontinent Pangea (see Figure 2). But for a mass extinction, the union of 2–3 lithospheric plates is enough, which can threaten the extinction of up to half of the species.

Similar processes proceed in the oceanic expanses, where a single ocean (Panthalassa) is formed instead of several geographically isolated oceans and seas. At the same time, the area of the shelf zone saturated with life significantly reduces.

When the continents diverge, the surviving species in the new conditions of geographical isolation give rise to a new round of evolution to surpass the previous one, since the most evolutionarily developed species adapted to changing environmental conditions participate therein.

In the future, the convergence of the continents in new geographical conditions leads to a new cycle of extinction and a subsequent increase in biodiversity during their divergence (isolation).

Therefore, the consolidation of the continents and the accompanying extinction contribute to the preservation and further evolution of the most adapted species, which, in the course of the subsequent separation of the continents, gave rise to new even more promising species.

A comparison of the times of mass extinctions and collisions of lithospheric plates (Table 2) shows that almost all five identified mass extinctions occurred after significant mergers of lithospheric plates up to the formation of a single supercontinent. It is important to note that the process of extinction due to interspecific competition is a very slow process that occurs over many generations of species.

Major mass extinction	Associations of the continents
Ordovician-Silurian extinction mass extinction	Formation of Laurussia (Euramerica), the Paleozoic supercontinent, as a result of the collision of the North American platform (the ancient continent of Laurentia) and the East European platform (the ancient continent of Baltica) during the Caledonian orogeny (500–400 Mya).
Late Devonian mass extinction	In the Devonian, the northern continents formed a single large continent (Atlantia), to the east of which was Asia. Gondwana continued to exist.
Permian-Triassic mass extinction	Pangaea formed in the second half of the Carboniferous and Permian (~ 300–180 Mya). This period was long and took place in several stages.
Triassic-Jurassic mass extinction	Collision of the continents broke away from Gondwana with parts of Laurasia.
Cretaceous-Paleogene (K-T) mass extinction	In the Paleogene (~ 65 Mya), the territory of Eurasia increased: the Sundian archipelago joined the mainland, the Balkan Peninsula formed a single whole with Asia Minor, Europe joined Africa in the area of modern Gibraltar, and there was a merging with the North America in the northwest.

Table 2.

Consolidations of lithospheric plates during mass extinctions.

4.1 Vertical tectonic movements and biodiversity

Similarly to the horizontal movements of lithospheric plates, the ascending and descending movements of Earth’s crust lead to transgression and regression of the seas, that is, the processes of amalgamation-separation of territories, and, accordingly, to changes in the factor of geographic isolation and biodiversity.

For example, the situation with the late Pleistocene extinction of megafauna in the period 20–4 thousand years ago (about 36% of large mammals died out in Northern Eurasia and about 72% did in North America) can be explained by the periodic formation of the Eurasia–America supercontinent due to the periodic formation and disappearance of the Bering Isthmus. It is known that over the past 3 million years, the territory of Beringia has risen and again submerged under water about 6 times [23]. The last time Eurasia and North America separated was 10–11 thousand years ago.

Before this, the isthmus had existed for 15–18 thousand years. Of the large herbivores, the mammoth and wooly rhinoceros became extinct at this time; of the large predators, giant sloths, saber-toothed lions, and cave bears died out.

5. Globalization as a factor in the extinction of species

The proposed mechanism of mass extinctions is also quite acceptable for explaining the current situation with biodiversity on our planet. The processes of globalization, which are actively developing owing to man, largely act similarly to the influence of the unification of continents, reducing the impact of the geographic isolation factor. The activation of accidental (invasion) and deliberate (introduction) movement of animals and plants with the help of humans leads to competition between species that find themselves within the same ecological niche, with the inevitable subsequent extinction of less adapted ones. Thus, in recent decades, there has been a steady increase in the number of invasive species [24], which undoubtedly contributes to the extinction of the natives.

In the context of globalization, island populations are at particular risk. For example, the communities of the islands of Madagascar, New Zealand, and many other isolated territories, unique in terms of biodiversity, are constantly threatened by the introduction of new species.

First of all, representatives of animals are threatened. Plant species are less sensitive to competitive exclusion and more resistant to land consolidation because the spread of plant spores and seeds is global due to birds and atmospheric transport.

6. Discussion

Mass extinctions of biological species represent one of the obscure problems of evolution, perhaps overdramatized. Nevertheless, the available paleontological data on biodiversity “depressions” in some periods of the history of the biosphere require clarification of the causes of such events.

The proposed fairly universal hypothesis of mass extinctions is capable of explaining the mechanism of reductions in biodiversity at certain stages of the history of the biosphere without being too dramatic.

They are the tectonic movements of Earth’s crust, which cause periodic consolidation and separation of lithospheric plates and, accordingly, change the degree of geographical isolation of species, which are proposed to consider as the major factor triggering the process of mass extinctions of species, which have repeatedly occurred in the history of the biosphere.

The mechanism of extinctions is implemented according to the competitive exclusion rule due to the growth of interspecific competition and the death of less adapted species in the conditions of a decrease in the diversity of ecological niches and the falling of different species into one ecological niche when lithospheric plates unite. This is especially clearly seen in the formation of supercontinents. With the separation of the lithospheric plates, a new progressive jump in speciation occurs, since the most competitive surviving species participate therein.

The removal of the isolation factor also explains the phenomenon of the Late Pleistocene extinction of megafauna in Northern Eurasia and North America as a result of the transgression and regression of the sea and the periodic unification of the old and new worlds.

It should be noted that data on the loss of plant species during periods of mass extinctions are usually less significant, which is associated with their lower migratory activity and, accordingly, with a significantly lower increase in competition when tectonic plates unite. For example, the periodic consolidation of the North American and Asian continents during the formation of the Bering Isthmus did not change the situation in the struggle for a “place under the Sun” for plants, and the exchange of their seeds and spores, for example, with the help of birds and wind, occurs even in the absence of the isthmus.

The tectonic hypothesis of the causes of mass extinctions also explains the long duration of the periods of mass extinctions, due to the fact that the extinction of species due to interspecific competition occurs during the change of a large number of generations.

Human activity, turning into an increasingly powerful geological factor, like the consolidation of lithospheric plates, has significantly reduced the isolation degree of biological species. During the period of globalization, due to introduction and invasion, migration processes have significantly accelerated, which inevitably leads to an increase in interspecific competition, to a decrease in biodiversity, and finally to a new mass extinction. There is no doubt that the process of global chemical and physical anthropogenic pollution of all components of the biosphere and the reduction of habitats of native species are superimposed on the said cause of, in fact, anthropogenic biological pollution.

The catastrophic natural processes considered in the literature as the primary source of mass extinctions undoubtedly played and continue to play a large role in reducing the number of species inhabiting the affected regions, but cannot fully explain the regularity of manifestations of global depressions in biodiversity dynamics and their duration.

Such cycles of mass extinctions of species during the unification of continents and jumps in speciation after the separation of the continents are evolutionary progress for the biosphere since the most surviving competitive species participate in a new round of speciation.

For final conclusions about the reality of the considered provisions, detailed comparisons of the periods of collision of tectonic plates (not only with the formation of supercontinents) and data on the biodiversity dynamics during these periods are required. At the same time, there are considerable limitations both from the side of dating the consolidations of tectonic plates and from the standpoint of assessing biodiversity during these periods.

Despite increasing scientific possibilities, many aspects of plate tectonics and the supercontinent cycle “cannot be demonstrated; even the number of supercontinents that may have existed prior to Pangea remains a matter of debate” ([16], p. 892). On the other hand, “any conclusions may be erroneous only because the paleontological record is a very small and nonrandom sample, which does not allow obtaining reliable information about the total ancient biota at a certain taxonomic level, and unreliable not only quantitatively, but even qualitatively” ([9], p. 8).

7. Conclusion

The considered material illustrates one more aspect of the influence of geological factors on the evolution of life on Earth. At the same time, the tectonic hypothesis of the causes of mass extinctions of species to the maximum extent, in comparison with other hypotheses, explains the features of these global phenomena, in particular:

1. the large proportion of extinct marine species, since when the plates merge, the area and diversity of shelf territories sharply reduce;

2. lack of reliable data on the extinction of plants, perhaps due to their less migratory ability, but greater globality due to the spread of their spores and seeds around the world by birds and atmospheric currents;

3. the jump in biodiversity following the extinction due to the increase in the diversity of ecological niches during the separation of the plates due to the participation of the most competitive species, which won;

4. long duration of mass extinctions due to the low speed of movement of lithospheric plates and the significant duration of the replacement of species in the process of interspecific competition;

5. recurrence of mass extinctions during the next association of lithospheric plates, which act as a trigger for increased competition, extinction of species, and subsequent growth of biodiversity when the plates are separated.

Further refinement of the periods of mass extinctions and periods of lithospheric plates joining divergence will make it possible to create a more accurate concept of the role of geological factors in the evolution of species and the dynamics of biodiversity.

Acknowledgments and funding sources

The work was supported by the state assignments of Lomonosov Moscow State University (AAAA-A16-116042010089-2) and the Institute of Basic Biological Problems RAS (FMRM-2022-0029).