by Alexei KAZDYM, Cand. Sc. (Geol. & Mineral), Senior Research Associate, Institute of Geoecology, Russian Academy of Sciences

Today most different scientists-geologists and ecologists, earth and soil scientists, geochemists and microbiologists - are closely involved with the earth's ecological problems. And yet they find out that biospheric pollution and modification of ecosystems caused by man occurred even aeons ago, in hoary antiquity. Negative environmental impacts forced primitive tribes to pull up stakes and move elsewhere.

Since 1997 the author of the present article has been studying technogenic depositions in the cultural (habitation) layer on the site of the present large cities (Moscow, St. Petersburg, Chelyabinsk, Smolensk, among others). Such depositions range in age from the thirteenth to the twentieth century. He is also concerned with ancient camping sites, settlements and protopolies (towns) - from the Upper (Late) Paleolithic to the 18th century B.C. and on up until the 1 lth century A.D. Habitation deposits are of interest not only to archeologists alone-they make it possible to reconstruct paleoecological environments, for the microstructure of these deposits is a sufficiently stable diagnostic indicator.

Both ecologists and archeologists have found common ground today at a cross-roads of sciences like soil study, geography, geomorphology, biology and geology. New interdisciplinary trends and sciences have appeared-suffice if we mention the archeological soil science, archeological geology (geoarcheology or archegeology), and archeological mineralogy. True, for the most part these are still lone-wolf studies carried out by individual enthusiasts or at best by small research teams. As a matter of fact, ecology and archeology are in close touch with a rather promising research trend - the paleoecology of primitive human societies and archeological ecology. It thus becomes possible to explain the causes of major popular migrations as large groups of people suddenly left their old habitats and trekked elsewhere. Many scientists relate such transmigrations to sudden climate coolings and desert encroachments. However, most paleoclimatic reconstructions over the past 5 to 7 thousand years (suggested by earth scientists by and large) are contradictory.

Questions related to the studies of underlying, buried soils, often not quite accurately dated by the radiocarbon analysis method (much in use for paleoclimatic reconstructions) still remain open. Allowing for an error of this method as well the rate of natural changes of landscape environment, we come to a paradoxical conclusion - the error margin may be in the range of 100 to 200 years, or three to four generations of people. This time is long

Articles in this rubric reflect the authors' opinion. - Ed.

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enough for a tribe either to adjust to a new situation (which is characteristic of some cultures) or to migrate to another, more suitable territory. Large-scale migrations (of nomadic tribes in the first place) are most likely caused not only by climatic changes but also by the cumulative effect of ecoproblems and environmental changes. Wherever this two-pronged effect was felt the hard way, the population had to move on.

For instance, the abrupt climate cooling and crop failures for years in succession at the turn of the 16th and 17th centuries (the reign of Czar Boris Godunov, 1598 - 1605, and the "Times of Troubles" after his death) forced large masses of the Russian population to move eastwards across the Urals into the forest-steppes of West Siberia with their extra-continental climate, that is very cold winters and hot summers.

In all likelihood global changes of the climate were not so dramatic and rapid (in Eurasia's steppe zone anyway) to make thousands of people with their flocks and herds, chattels and all leave their familiar spots and seek their fortune elsewhere. There must have been some ecological problem behind that - a problem the way we understand it now, empirical so far and not proved in full.

As historians and geographers see it, migrations are not only a historical phenomenon - it is a geographical one, too, connected with anthropogenic landscape modification. People often settled territories similar to their former homelands which they had to leave. Thus, in the 1 lth century Yakuts moved to the Lena river valley and started breeding horses there as they had done it in their old habitats on the shores of Lake Baikal; however, they would not settle the watersheds of the taiga woodland populated by Evenks. In the 17th and 18th centuries Russian explorers crossed all of Siberia but settled down in the forest-steppe margin of the taiga forestland and in river valleys, that is landscapes like those in their native lands in European Russia.

Nomadic and seminomadic tribes of the forest-steppe and steppe zones-from the pusztas of Hungary in the west to the steppes of Mongolia in the east-exhausted to some extent the ecosystems of the plainlands. The environmental degradation problem caused by cattle and sheep grazing came up there more than five thousand years ago. Favorable climatic conditions in the zone of steppes and forest-steppes 3 to 4 thousand years ago touched off a population explosion accompanied by a rapid rise in the livestock population.

In the Bronze Age (ca. 4 - 3.5 thousand years ago) Eurasian steppes were populated by seminomadic tribes for the most part who had relied on a string of settlements or protopolies that served as religious-social or religious-political centers. We can see that in the example of what is called

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the "Land of Towns" in the southern Urals and eastward (the protopolies Arkaim, Sintashty, Bersuat, and others).* Judging by archeological and paleoantological data, animal husbandry was the main trade of the aboriginals. They raised bovine animals (beeves, 43 - 60 percent), smalls (24 - 48 percent) and horses (6 - 25 percent). Needless to say, the livestock population was up in favorable years. This in turn improved people's life and contributed to population growth. Now, how many animals could feed within a particular ecosystem and how many people could subsist on natural resources? As ethnographers and historians estimate it, an average nomad family of five should have a livestock population equivalent to 25 horses, with one horse standing for five cows, and one cow-for eight sheep.

Supposing that at its initial stage a protopoly numbered 100 people (twenty families with 5 souls each). Which means they had to tend at least 300 horses and about 1,000 sheep. But what if there were as many as 500, and the poly's numbers increased from year to year? Say, every year 25 new-born babies survived (or 5 percent of the total population, which is a natural birth-rate). In five years the population increase would amount to 125 people (excluding parity progression). The cattle and sheep population should be up accordingly, for otherwise the tribe would be in for famine, and the death-rate would have risen dramatically. Hence the following pattern is obtained: better well-being→more of the cattle and smalls→population in-crease→higher pressure on the biogeocenosis→shrinking fodder base for the livestocks→declining population numbers and a possible exodus→abandoned protopoly→subsequent long self-rehabilitation of the territory in and around the protopoly (if it was possible at all).

It is pertinent to ask: Where are the figures from? Say, on the livestock population? There is hard archeological evidence on that. Digging in the Bolshekaragan burial grounds (Chelyabinsk region just east of the Urals), archeologists and osteologists (the latter studying the structure, growth and changes of bone skeletons) hit upon a large mass of bones belonging to domestic animals. According to tentative estimates, as many as 24 cows, 12 horses, 45 sheep and 11 goats were immolated and buried together with their lord. Such sacrificial killing would never have been done to the detriment of the tribe's well-being. In fact the steppe abounds in burial grounds and mounds like that, with only a few ones discovered or studied well enough.

Now, how reliable are the estimates of the productivity of ancient ecosystems? This is an important problem. The depletion of natural resources (in a definite region or locally, at a definite time) may be connected with long spells of favorable climate. The population of domestic animals

* See: A. Pshenichnyuk, "'Royal' Mound in the Southern Urals", Science in Russia, No. 3, 1999. - Ed.

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could be large enough to cause soil degradation because of overgrazing, trampling and livestock overlanding as a result. An ecosystem could be depleted in 20 to 30 years, with the situation compounded by soil salinization, a decrease in the number of fresh water sources-also due to the felling of relict forests and those growing in flood-lands for construction purposes, and the destruction of reed and rush thickets. So local tribes had to move on and on, leaving vast tracts of land (hundreds of thousands of square kilometers in area) no good for stock-breeding. So there was no way out-either pull up stakes and move or take up some other occupation rather than vanish from the face of the earth. At this stage we have no method of telling for sure the degree of an ecosystem's imbalance or its capacity for self-rehabilitation. But scientists are making the first (not timid at all!) steps toward this end; and they have obtained evidence confirming the hypothesis on man's potent impact on the environment in times out of mind.

What with a small density of the human population (in the Bronze and in the early Iron Age the population density was about 1 per 1,000 km² in the steppe zone) that changed its habitation territories now and then, steppe landscape environments were still capable of self-recovery (though on a partial basis, if seems). Yet the problem of overgrazing and overlanding was acute near the protopoly settlements, the scene of vegetation destruction, salinization and degradation of soil.

We know that the overpopulation of ungulates is ruinous for steppelands. The plants consumed by herbivorous animals, sheep and goats in particular, cannot make a recovery in good time, they are unable to accumulate essential nutrient substances, and have trouble reproducing. Meadow grasses suffer worst of all, but sheep's fescue and sedgeless. The hardiest plants (spurge, Kochia prostrate, wormwood), the steppeland perennials, not consumed as much by herbivores, proliferate and occupy the free ecological niches.

Trampling is also a major hazard for steppeland vegetation preventing it from natural reproduction. One sheep alone covering something like ten kilometers daily, leaves as many as 40,000 hoof prints, its hooves damage around 200 sq. m of the cover. Bovine animals, too, damage the topsoil and vegetation cover, especially near bodies of water (lakes, ponds, rivers), fords, and footpaths. Cowtrails often turn into ravines.

Steppe productivity declines two- to fourfold in consequence of overgrazing. Apparently smalls (sheep, goats) as well as some of the beeves were kept and grazed right near settlements, 5 to 10 km outside a protopoly, and the human impact on the environment was the strongest there.

As shown by archeological data collected in the "Land of Towns", each large poly was surrounded by smaller settlements, so that the anthropogenic impact area tended to go up. Besides, drinking places had to be there on pastures or next to them at a distance of 1 to 3 km for cows, 3 km for

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sheep, and 4 km for horses; the ground about these places was trampled down.

The problem of soil overmoistening is particularly felt, especially next to livestock housing places. Sheep dung and urine are very aggressive, contain as they do up to 0.85 percent of pure nitrogen, 0.33 percent of phosphoric acid, 0.67 percent of potassium and 0.8 percent of calcium salts. The acid medium thus formed kills microorganisms in the soil and causes microelements to migrate beyond the soil profile, and the topsoil degrades as a result. Acid media stimulate the transport of calcium carbonates which act as a kind of buffer in steppelands.

The most intensive anthropogenic impacts did not seem to affect all of the area bordering on polies except particular places like corrals (wintering or summering yards, sheep pens or barns) within walking distance. In the steppe the average speed of a herd's (or flock's) movement is not above 3 to 4 km/h (five to 6 hours a day), and it is from 15 to 25 km/h for horses. Longer cattle and sheep overlandings are both taxing and unprofitable, and therefore cattle-raisers and shepherds did not go father than 15 kilometers away from their poly.

"Background" soils under burial grounds were also affected, as shown by excavation data (such soils are rather easily dated by archeological evidence, and that is why paleosoil scientists use them for comparative studies). A phytolitic analysis of samples dug up from the Zunda-Tolga mounds in Kalmykia demonstrate that with the advent of catacomb culture tribes in the Bronze Age the virgin soil was subjected to considerable anthropogenic stress. Cattle- and sheep-sick pastures turned into semi-desert, saline and badly eroded expanses in less than 200 years. Such abrupt landscape modifications in a relatively short period like this can hardly been explained by global natural and climatic factors alone - the human population likewise had a finger in the pie.

Desert encroachment (desertification) on a local scale in our times, too, is a rather vigorous process taking between 20 and 25 years; as we have said, it is largely caused by degradation of the top soil. Blown off by violent winds, the soil cover gets pockmarked with deflation basins where, because of the presence of subsoil waters nearby, primary salting of the soil becomes possible. Thereupon windblown salt dust contaminates large areas, as seen in the example of steppes in the Republic of Kalmykia north of the Caspian.* In 1956 the barren wastes of the Black Lands made up 4 percent of the republic's area. Today this figure is up to about 90 percent owing to the larger sheep population and grazing malpractices. The number of pastures has dropped to one-tenth of what it used to be, while the human and cattle populations have marked a dramatic increase to speed up the desertification process. In a mere

* See: N. Yelansky, '"Will Climatic Warming Save Kalmykia?", Science in Russia, No. 2, 2004. - Ed.

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50 years almost 85 percent of pastures have turned into sandy desertlands.

Anthropogenic effects on natural environments are glaringly manifest in the forest-steppe, steppe and semidesert ecosystems. In the past 100 to 200 years the American prairies as well as the steppes of Western Siberia and Kazakhstan have been plowed up, with soil erosion spreading to extensive land areas. Africa's savannahs* have degenerated into barren wastelands; the felling of tropical forests has had an adverse effect on the vast expanses of Southeast and Southwest Asia, and on the Amazon selva (tropical woodland).

But back to the ancient times. Towns and settlements rising up in steppelands led to a powerful impact on the natural environment. The long existence of such urban centers coupled with the technogenic action exerted by the population taxed biogeocenoses, and in some cases caused a letup in urban activities and compelled town-dwellers to migrate.

The degeneration or utter disappearance of many great civilizations seems most likely to be related to the depletion of natural resources, as we can see it in the example of Ancient Egypt, Mesopotamia, the Harappa Civilization in India, and other civilizations. Land-tillers of the early Middle Ages modified as good as the entire natural environment of Europe (though the first changes had been wrought back in the Roman times); the greater part of its territory nowadays is under man-made, not natural, landscapes. About 80 percent of forests on the Apennine Peninsula and the beech groves of Gallia were hewn out still in the Roman Empire; in Hellas goat herds destroyed vegetation on the Aegean Sea islands.

The pollution of the ancient cultural deposits underlying the present technogenic strata may exceed all permissible levels. Archeologists find a high concentration of phosphorus, lead, zinc, copper, arsenic, cadmium, manganese, magnesium and other elements-all that thanks to the presence of humans there. For instance, the enhanced concentration of lead (occasionally hundreds and thousands of times above permissible standards) could be connected with the making of pottery and pipes, ceramic glaze and various dyes (like white lead or zinc white, for instance). The excess of iron, cobalt, manganese and other metals indicates the trace amounts of melting slags once present in the habitation deposits at a high concentration. The abnormally high content of arsenic was registered in tanneries and grain storage barns-this poison was needed for tanning and annihilation of rodents. Copper and zinc are indicative of copper smelting and minting, and mercury-of the jewelry industry.

Most of the deleterious elements used in ancient townships and other communities occur in the form of various compounds and minerals. Many are very poisonous-like, for example, the well-known malachite (copper carbonate), which is good as trim stone and raw material in the production of dyes: its dust may cause really bad poisoning. Likewise poisonous are certain sulphates of copper (chalcanthite) and iron (melanterite, coquimbite) as well as the widespread sulphides of iron like troilite, gragite, pyrite.

Hydrogen sulphide, sulphuric acid and some organic acids; ammonia and methane (all that released with the decomposition of organic matter) react with metal items to produce inorganic and heteroorganic compounds. Carbonates (calcite, aragonite, siderite), phosphates of iron and calcium as well as other neogenic minerals are of common occurrence in urbanized territories; some are associated with pathogenic microorganisms.

Suchlike processes took place in ancient burial places, too. For instance, digging in the burial complexes Kirsa and Pobeda in the Chelyabinsk region (5th century B.C.) archeologists have found a variety of neogenic minerals on pieces of leather clothes, on bone, arrow shafts, wood (turquoise, malachite, chalcopyrite, siderite, arsenopyrite and many other minerals).

The examination of metal articles recovered from the Sopininsky burial mound in the Kurgan region (4th-5th centuries, the early Iron Age) indicates the presence of iron oxides (lepidocrocite, goethite, hematite), siderite as well as greenalite - a rather rare metacolloidal mineral. Mineral dyes, too, are often found in burial grounds-such as realgar (red arsenic), cinnabar, orpiment, even mercury.

Geochemical anomalies combined with specific microbiological environments, alongside anaerobic (oxygen-free) media, anthropogenic microorganisms as well as definite physicochemical characteristics (alkaline pH shift) - all that is conducive to the formation of technogenic minerals and mineral associations.

It should be stressed that organic matter in cultural layers preserves quite well in the absence of oxygen. Thus, trace amounts of manure dating from the mid-18th century were found during archeological excavations in Chelyabinsk - the dung was in excellent condition, mind you! Such kind of "finds" (like cesspools) were dug up under Moscow's Manege** in 2004. Habitation depositions may conceal certain pathogenic bacteria dangerous to man even now.

Thorough ecological tests are therefore necessary prior to archeological excavations so as to spot zones of ancient pollutions and take required sanitary-hygienic precautions for the digging and building crews, archeologists and all local residents. It stands to reason that all this work should be supervised by competent archeologists.

* See: Ye. Demin, V. Kushin, '"Attack on Desert", Science in Russia, No. 4, 2004. - Ed.

** See: A. Veksler, "Archeological Finds in the Heart of Moscow", Science in Russia, No. 6, 2004. - Ed.

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