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by Rudolf BALANDIN, geologist
Climate is a statistically generalized description of weather conditions. It used to be considered stable within the life span of one single generation. In these past fifty years, however, the situation has changed, what with weather vagaries everywhere and the ongoing global warming, according to many competent experts. What is the cause of this warming? Its possible consequences? Some of the clues are offered in a capital study off the press here in this country (Climate in the Ages of Major Biospheric Reconstructions; M., Nauka Publishers, 2004; 299 pp.).
The geologic history of our planet is characterized by predominantly warm periods alternating with cold spells now and then. That has led to cardinal structural changes of natural zones and landscapes and to the appearance of ice sheets (caps) spreading from circumpolar regions down to lower latitudes.*
Now what caused such changes, and how did they proceed? The book under review furnishes a wealth of information to this effect and is illustrated by a picture of paleoclimatic succession of events, maps, charts, and so forth. The authors seek to explain the peculiarities of climate dynamics as an important factor of biological life.
The book is in four parts, each dealing with changes that occurred in the natural environment at the turning-points of geologic epochs. Looking through paleographical maps you kind of travel back into the distant past to see the changeability of the face of the earth: its continents moving here and there, its climatic belts, land-and-sea balance changing out of recognition. You just wonder: there is another planet before you, poles apart from what we are having today-its surface, land and ocean contours, and many other things are so much different.
The first part of the book (author, Mikhail Akhmeyev) considers the period of transition from the warm biosphere to a colder one during the Paleogene (65 - 23 mn years ago). The second, much more extensive (authors: Nikolai Chumakov, Mikhail Zharkov, Ivan Murdmaa, Nadezhda Filatova, Alexei Hermann, Kirilla Kuznetsova, Oleg Korchagin) looks into climatic fluctuations taking place in the Jurassic and Cretaceous (213-
* See: A. Velichko, "Climatic Warming: Glimpse into the Future", Science in Russia, No. 3, 2002. - Ed.
Paleoclimatic overview. Cretaceous, Barriassic (simplified). Climatic belts: high-latitudinal moderate humid (NM - northern, SM -southern); mid-latitudinal warm humid (NW - northern, SW - southern); tropical-equatorial arid (ТЕ); tropical arid hot (NA - northern, SA - southern); equatorial humid (E, EQ); ES - Euro-Sinayan region; A - Australia.
65 mn years ago) when "hothouse" conditions prevailed on a global scale. The third chapter (authors: Mikhail Zharkov, Ernest Leven, Sergei Naugolnykh, Nikolai Chumakov) takes us back to the age of global cooling (286 - 243 mn years ago). And the final, fifth, chapter reconstitutes the succession of climatic and biospheric events of the Late Precambrian (1 - 0.55 bn years ago). This study offers copious and diverse material, factual pieces of evidence including. Earth scientists are never tired of putting forward hypotheses and theories so as to get to know the causes and motive forces behind the most dramatic biospheric changes. Naturally certain moot points are unavoidable every now and then: after all, truth is born in heated discussions and clashes of opinion, not in stating the obvious.
This monograph makes you stop and query the notions so much in vogue of late about sudden global cataclysms (in the same vein as the theory of catastrophes advanced by the French zoologist and geologist George Cuvier, 1769 - 1832) triggered, say, by a fall of an asteroid followed by biospheric stress, mass deaths, and that kind of horrors. We do not exclude the possibility of periodic "bombardments" of the terrestrial surface by meteorites and even small asteroids, for there are real facts of such impacts.* And yet we should not exaggerate their significance in the evolution of plants and animals. It has seen an irregular course throughout the geologic history of our planet, this evolution. It has seen active periods when particular forms of life die out and are replaced by others. Such events, related by and large to overall global changes, follow a sluggish course; besides, they are connected with the subtle dynamics and fickle structure of "living matter" (which, according to Vladimir Vernadsky, is a totality of organisms).
The authors of the work under review have done a good job in reproducing the succession of paleographic events. Still, there are questions in what concerns geological indeterminacy. The chronicle of the biosphere is reconstituted from a set of characteristics (fossils and soils, the composition, structure and conditions of rock occurrence). We know that even in well-studied outcroppings a considerable part of deposits is absent due to breaks in the accumulation of sediments or else because they have been destroyed by erosion. Besides, we have to deal with random and odd data from regions hundreds and even thousands of kilometers apart, something that interferes with the accuracy of geochronological methods of dating. Furthermore, it is difficult to take account of local climatic factors which depend not only on latitudinal, but also on vertical zonality. Microrelief features play a part, too.
And yet another essential consideration. It has been proved that in the last 10 to 15 thousand years there have been significant climate changes in some regions, e.g. in Sahara: a savannah plain of many rivers, lakes and marshes, it turned into a barren desert-land.** Landscapes have changed beyond recognition without man's interference. Can we trace vigorous processes like that by reproducing the succession of geological events? If we can't, the degree of indeterminacy (uncertainty) ought to be taken into account then.
The authors took into consideration-insofar as it was possible-these and many other things. However,
* See: A. Litvak et al., "Space Wanderers", Science in Russia, No. 2, 2003. - Ed.
** See: Ye. Dyomin et al., "Cyclone Over Sahara", Science in Russia, No. 4, 2003. - Ed.
Paleoclimatic shorthand. Cretaceous, MaastrichAge (same characters).
they supplied only one paleographical map version for each epoch in particular. This approach is justified for the last few millions of years, for no essential changes, could have occurred in the position of continents and partly oceanic currents during this time. But the picture is different for more distant periods when the appearance of dry land was quite otherwise. Now it merged into a solid supercontinent, now it broke up into parts. Reproducing the exact dimensions, outlines and relief features of the erstwhile lands seems hardly possible. Therefore it would be advisable in some cases to come up with two or three versions of paleographical maps.
We are puzzled a bit by what Dr. Chumakov calls a "persistent glaciosphere", i.e. ice sheets, underground glaciation, the old ice and snow of plains and seas. But do we need a new term, what with the other one - cryosphere - adopted long ago (introduced by Andrei Dobrowolski, a Polish geographer, in 1924)? Acad. Vernadsky as well as his friend and pupil Boris Lichkov made use of it; by the way, Dr. Lichkov is the author of a pioneering study (1935) in which he saw a connection of biospheric reconstructions with tectonics and continental migration (drift). He was the first to study the variations of hydrological and hydro-geological conditions in the past, something that has a direct bearing on our subject-matter.
It would have been useful to show, be it only in broad outline, how paleogeographers have changed their views with time, and what concepts they have propounded. The history of science has always been a wellspring of fresh ideas. It helps shake off the enchantment of new-fangled theories and hypotheses. Let us recall the words of the great chemist and thinker Dmitry Mendeleyev: "Real science is what has come to stay after so many doubts and all kinds of tests and trials (observations and experiments, numbers and logic); you'd better not trust overmuch the 'latest word' in science..."
Alexei Hermann followed this advice: proceeding from an in-depth study of plants of the Late Cretaceous (113 - 87 mn years ago), he disproved computer simulation results. In his words, computer simulation "cannot reproduce the picture of climatic events in mainland Asia under the conditions of greenhouse climate on the basis of geologic evidence alone." Paleontologic data are certainly primary. Dr. Hermann has made a cogent description of the strategy of vital activity of plants in the warm biosphere during the polar night.
But how could we explain the errors of computer simulation models showing the starkly continental conditions (judging by the flora remains) to have been much milder? The monograph gives no answer, though this question is important for understanding the present-day climatic conditions, too. As Acad. Valentin Dymnikov sees it, mathematical modeling leaves out the global geochemical cycles of carbon which have a substantial effect on the state of the biosphere.* That's what the great Swedish scientist Svante Arrhenius wrote about a hundred years ago. And, as Acad. Vernadsky noted: "The amount of CO2 liberated from the biocycle in the form of calcium carbonate and preserved as such is hundreds of times larger than the total amount of carbon dioxide present at this moment in the atmosphere, in the ocean, in living matter..." Carbon gets into the crust as hard coal, too. As to carbon dioxide (CO2 ), it belongs to greenhouse gases
* See: V. Dymnikov, "Computer Models of Terrestrial Processes", Science in Russia, No. 3, 2004. - Ed.
not transparent to UV radiation of the sun and terrestrial surface. Consequently, the abundance of this gas in the air makes the global climate milder and more even; however, when too much carbon has accumulated in the crust, the climate becomes colder and contrasting.
If so, climate changes should proceed gradually, the way it was in the epochs of global changes of the biosphere. Says M. Zharkov: "The essential invariability of the spatial position of the principal paleographical elements of the earth in the Permian and in the Early Triassic invites the supposition that changes of this stage of geological history were not due to any rapid and cardinal paleotectonic and paleographic events. Apparently reconstructions were caused by long and consecutive global changes that occurred on Pangaea* and that changed but slowly its links with the ambient seas and oceans."
Now why did the "geologic winter" come to an end and the biosphere got warmer? It would have made sense to look into two old ideas which we have already mentioned: the migration of continents and the geochemical cycle of carbon. But according to Dr. Chumakov, the main cause of that great change lay in the grandiose bursts of volcanic activity whereby a huge amount of hothouse gases was ejected into the atmosphere to cause a temperature rise. The author, however, does not cite even approximate figures to this effect, without which his hypothesis could hardly be well-validated enough.
Dr. Chumakov explains the onset of "geologic winter" by the intensification of volcanism responsible for a dust loading of the atmosphere, which prevented a large part of solar radiation from reaching the earth's surface. But when the air cleared up and more of the hothouse gases came to be released from underground rock, a global warming set in.
Such hypotheses revive the views of the plutonists (from Pluto, in Greek Mythology the lord of the dead and the lower world) who in the 18th century put down every kind of change to plutonic phenomena deep under. Today one sets much store by outbursts of heat flows (plumes) from the earth's mantle, which is quite in line with the
* Pangaea - a hypothetical supercontinent that united all the present continents in the Paleozoic and Mesozoic. It is thought to have broken up between the Late Precambrian and the Ordovician, giving rise to four or more continents with intervening oceans. - Ed.
Paleoclimatic zonality picture in the early Permian (after N. Chumakov, M. Zharkov), with migration of continents (above), and on present-day data. Climatic belts: a - hot and arid, em - equatorial/mountain, et - equatorial/tropical, temp. -temperate, gl - glacial; A - North Eastern Asia, Аи - Australia, An - Antarctica, Af - Africa, E - Europe, I - India, Na - North America, Sa - South America
theory of global plate tectonics* that has gained much popularity in the past few decades.
It would be appropriate, however, to recall the opinion of Acad. Vernadsky, the author of the teaching on the biosphere, who thought that it exists and develops thanks to a flux of solar energy, thousands of times as high as the heat released from the earth's interior. "Life is truly one of the most potent geochemical forces of our planet, and the biogenic mutation of atoms it causes is actually a form of paramount orderliness in the biosphere's structure." Major structural changes are not only possible there, they are most likely because of the outer (exogenic), not the plutonic geologic processes alone. These are not ruled out either, of course, but they can hardly play a decisive role.
The ongoing global warming is an eloquent case in point. In the opinion of most experts**, it has been caused by human activity (technogenesis), though natural climatic variations are not excluded either. To clarify this problem, it is advisable to trace back the succession of events that led to the Recent Ice Age. Reproducing these events, Mikhail Akhmetyev, one of the authors of the book under review, concludes: A warm biosphere still persisted about 40 mn years ago. In that period, the Eocene, the temperature of the ocean near the North Pole was as high as 18 - 20 degrees on the centigrade scale, and our planet's climate was 5 degrees warmer than it is today. Thereupon it became ever more continental, with natural zones moving toward the equator. The final isolation of the Antarctic continent around the South Pole contributed to its glaciation. The buildup of huge masses of ice on dry land and continental shelf caused a recession of the World Ocean. The water areas of inland seas of the Northern Hemisphere shrank, and the West Siberian Sea dried up. The Arctic Ocean came to be isolated in part, and its waters cooled...
In this case, as Dr. Akhmetyev demonstrated for the territory of Kazakhstan, the climate changes were smooth, with some fluctuations now and then. The global temperature fall continued for more than 30 mn years, a period when major transformations of the terrestrial surface could occur due to the migration of continents, the growth of mountain ranges, the overall rise of land, and many other factors like the dropping level of the World Ocean, the changing system of sea currents, the deformation of the geoid (a hypothetical figure of the earth with the entire surface represented as at mean sea level) under the action of galactic forces or variations in the rotational rate of the earth... We could go on with this list. But in Dr. Chumkov's view, the chief cause resides in the weaker hotgas flow from the bowels of the earth (along with the effect of carbon-containing compounds accumulated in the earth crust).
M. Chumakov, it seems, wants to marry paleographical data to tenets of the global plate tectonics theory. He underrates the influence of the vital activity of organisms on processes taking place in the biosphere, even though this global system is an active accumulator and transformer of radiant solar energy owing to what we call the "film of life", plants and bacteria first and foremost.
Such views may appear obsolete, out of keeping with the latest postu-
* See: V. Trubitsyn, "Global Plate Tectonics: New Turn?", Science in Russia, No. 2, 2003. - Ed.
** See: Yu. A. Izrael, "Threat of Climatic Catastrophe", Science in Russia, No. 4, 2004. - Ed.
lates of plate tectonics. However, no one has ever refuted the basic points of the teaching on the biosphere- quite the contrary, they are being confirmed by hard evidence.* We might as well recall that in the previous warm epoch the globe saw a vigorous buildup of carbon-rich deposits, coal in particular, a process instrumental in bringing down the concentration of greenhouse gases in the air. The predominance of land continents in the Northern hemisphere and the relative isolation of the Arctic Ocean contributed to the continental glaciation of northern Eurasia and America.
The question about the causes of global warming and cooling in geologic history is still open. If man's technogenic activity has been able to change the composition of the atmosphere that much in a short time, the same scenario could have occurred within far longer stretches of time under the effect of the vital activity of organisms.
Be that it may, regardless of their approaches to the subject-matter, views and hypotheses, the authors of the monograph we have reviewed have succeeded in assessing a vast body of factual material on historical geology, paleontology, biostratigraphy, paleoclimatology and other disciplines. Thus, one of the authors (Sergei Naugolnykh) has adduced data on fossil soils making it possible to obtain a comprehensive picture of the natural conditions of the past. Indeed, Vassily Dokuchayev, an eminent natural scientist of the 19th century, has called soil a landscape mirror.
The authors make this conclusion: "Climate changes are a component element of all biospheric reconstructions, their 'trigger', preparation or first cause." And we would rather add: there is also a feedback, and therefore modification of the vital medium, the biosphere, climate including, could have been caused by the activity of "living matter", the chief transformer of cosmic (solar) energy.
Illustrations supplied by the author
* See: R. Balandin, "Geophysic Models and Reality", Science in Russia, No. 2, 2004. - Ed.
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