A recently developed technique yields new information 



on environmental changes affecting prehistoric 



Indians of the Southwest 



The Archaeology 



i 



o 



Environmental Change 



James Schoenwetter, Field Assistant 

 1 960 Southwestern Archaeological Expedition 



What would the people of Chicago 

 do if the present climatic bound- 

 aries within the United States were to 

 shift ten degrees latitude to the north 

 over the next twenty-five years? 



Would we meet the challenge in the 

 same way as the prehistoric Indians of 

 the Southwest, whose struggles to adjust 

 their patterns of living and to survive in 

 a rapidly changing climate have recently 

 been reconstructed by Chicago Natural 

 History Museum archaeologists? 



These are not idle speculations, since 

 some scientists believe that a northward 

 movement of climates is taking place now. 

 If this is the case, Chicago, which was 

 once buried beneath a great glacier but 

 today has a temperate climate, may 

 gradually grow warmer. While we 

 would enjoy milder winters, the corn 

 and wheat belts of the Midwest would 

 shift to different locations. Michigan 

 and Minnesota farmers would begin to 

 grow more corn, while farmers in cen- 

 tral Illinois would be planting cotton. 

 In a few years grain elevators in Kansas 

 would be nearly empty, while new ele- 

 vators would have to be built in Mon- 

 tana and North Dakota. Many industries 

 that depend on such natural products as 

 lumber or cotton would be far from their 

 sources of supply; our railroads would be 

 concentrated in the wrong places; our 

 towns and villages cut off from their eco- 

 nomic bases; and more of our nation's 

 land would become arid waste. 



Just as we recognize that environment 

 plays an important role in the life of con- 

 temporary people — whether civilized or 



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primitive — so we know that it must have 

 influenced man's life in the past. Re- 

 cently, the Museum's Department of An- 

 thropology has been investigating the 

 effect of environment on the lives of pre- 

 historic Indians in the southwestern part 

 of the United States. We are trying to 

 discover what climate these people might 

 have lived under, whether that climate 

 changed, and, if so, what the people did 

 about it. For if a climatic alteration 

 would create hardships for our society, 

 with all its intricate technological knowl- 

 edge and skills, there is little doubt that 

 a group of Indians living in an adobe 

 pueblo in thirteenth century Arizona 

 would have a more difficult time adjust- 

 ing to change in their surroundings. 



There are a number of techniques that 

 scientists may use to uncover information 

 about prehistoric environments. The 

 most widely utilized is the interpretation 

 of geological information. Through ob- 

 servation and study of the broad, flat 

 plain that extends from northern Can- 

 ada to central Illinois, the deep basins 

 of the Great Lakes, and the moraines 

 stretching across the center of the con- 

 tinent, we conclude that at one time a 

 great sheet of ice must have been pres- 

 ent in these latitudes, which ground the 

 earth's surface flat, gouged out the Great 

 Lakes, and deposited the terminal mo- 

 raines. 



Another technique is the interpreta- 

 tion of animal remains. At a village site 

 several miles from the present course of 

 a river many clam shells, fish and water- 

 fowl bones, and shells of aquatic snails 



may be found. We infer that at one 

 time the course of the river must have 

 been nearer to the site than at present. 



There is yet another major technique : 

 the interpretation of ancient plant re- 

 mains. This has generally been applied 

 to such materials as seeds, fruits, twigs, 

 and leaves, but these are rarely preserved 

 in sufficient quantity to be useful. Since 

 plants are quite good indicators of en- 

 vironment, as any of us will realize if we 

 travel from the temperate forest area of 

 Illinois to the arid deserts of the South- 

 west, the lack of such plant remains has 

 been a hindrance to prehistorians. 



Less than fifty years ago a Scandina- 

 vian scientist, Lennart Yon Post, discov- 

 ered a new type of plant fossil — ancient 

 pollen grains. It had been known for 

 some time that the pollen of plants is dis- 

 tinctively shaped and sculptured so that 

 it is possible to differentiate between gen- 

 era of plants (for example between pine, 

 spruce, fir, oak, ragweed, and morning- 

 glory) merely from an examination of 

 the pollen grains. The next step was the 

 discovery by Von Post that pollen grains 

 buried in sediment over thousands or 

 millions of years of geologic time some- 

 times were perfectly preserved and could 

 be identified as readily as pollen that 

 was fresh and new. But pollen grains 

 are microscopic, the largest being about 

 two-tenths of a millimeter, so methods 

 had to be devised for separating the pol- 

 len from the sediment so that the fossil 

 grains could be observed through the 

 microscope. 



Present techniques of pollen extraction 

 are based upon the knowledge that pol- 

 len grains are highly resistant to chem- 

 ical decomposition. In fact, pollen will 

 not dissolve in any of our most powerful 

 acids or bases, and since it does not dis- 

 solve chemists have not yet determined 

 the exact chemical composition of this 

 material. We extract pollen from sedi- 

 ment, then, by chemically decomposing 

 the sediment and leaving the pollen be- 

 hind. As an example, many sediments 

 contain calcium carbonate, the mineral 

 which causes boiler scale. Hydrochloric 

 acid dissolves this mineral, much as sugar 

 dissolves in a cup of coffee. By adding 

 this acid to the sediment and then spin- 

 ning the soupy liquid in a centrifuge we 

 can force the undissolved material to the 

 bottom of a test tube and pour off the 



