April, 19S3 



FIELD MUSEUM NEWS 



Pages 



THE AGE OF THE EARTH 



By Sharat K. Roy 

 Assistant Curator of Invertebrate Paleontology 



How old is the earth and how may one 

 know its age? This question has perplexed 

 humanity for centuries. James Hutton, one 

 of the founders of geological science, despair- 

 ingly declared, "No vestige of a beginning — 

 no prospect of an end." Since his time, 

 however, geology has progressed rapidly, 

 and various methods have been advanced 

 to estimate the earth's age. 



The oldest method was based on the 

 rate at which land was eroded and deposited 

 in the seas, estimates being made by taking 

 the observed thickness of the entire geologic 

 column and dividing by the rate at which 

 sediments are now being laid down. Early 

 in this century several such estimates were 

 made, and the earth's age, since solidification 

 from its molten stage, was computed at 

 100,000,000 years. However, this figure 

 was challenged because, to begin with, 

 there is no trustworthy starting point for 

 reckoning the total thickness of the sedi- 

 ments. Secondly, the rate of sedimentation, 

 due to changes in climate and in the eleva- 

 tion of land, has varied through the ages. 

 Finally, there is no record of the vast length 

 of time that has elapsed between the periods 

 of sedimentation. 



Another method once used by geologists 

 and geo-chemists was based on the rate at 

 which salts were dissolved from the lands 

 and accumulated in the oceans. The total 

 amount of salts in the oceans was divided 

 by the present rate of annual supply. This 

 method gives an age estimate about the 

 same as that based on the rate of sedimenta- 

 tion. But again difficulties appear. Neither 

 the area of the continents nor their relief 

 in the past was the same as today. Hence, 

 the stream gradient and its power of dis- 

 solving salts from the land surfaces have 

 not been the same. Also, it is not known 

 how much salt the ocean derived from 

 other sources, such as the shore line, ocean 

 beds, and volcanic actions. Nor is it known 

 if the oceans were essentially uniform in 

 volume throughout the ages or if they 

 grew to their present volume from a small 

 beginning. 



Still another method of computation was 

 based on the rate at which one species of 

 life changed to another in successive geo- 

 logical periods. The physical history of 

 the earth was divided into twelve periods, 

 and it was assumed that 20,000,000 years 

 were required for an entire change in the 

 species of each period, or 240,000,000 years 

 in all. This, however, did not include the 

 time before life existed on the earth. Further- 

 more, while our conception of the passage 

 of one species to another is well founded, 

 the rate of change has varied according to 

 species. On the one hand we have records 

 of species which have withstood all possible 

 environmental changes, and, on the contrary, 

 we know of types of life which have yielded 

 so rapidly to change that their evolution 

 is almost explosive. With these conflicting 

 evidences, it is hardly possible to use this 

 paleontological record as a basis for a 

 concrete expression of geologic time. 



Other methods likewise have been used 

 but were unable to withstand critical 

 analyses, because the uniformity of the 

 rate of action which is the criterion for 

 computing geological time could not be 

 relied upon. Nevertheless, the search for 

 a process in nature that takes place in 

 direction only, and does not change its 

 rate of action, eventually was discovered. 

 Not long ago, it was experimentally proved 



that such a process was present in the 

 atomic disintegration of various radio-active 

 elements contained in certain rocks and 

 minerals. This opportune and valuable 

 discovery has become the present accepted 

 basis for measuring the age of the earth, 

 and has given excellent results. 



The radio-active minerals are commonly 

 found in igneous rocks. The parents of 

 the whole series of radio-active minerals are 

 uranium and thorium. Each of these 

 parental elements transforms through a 

 succession of changes. The final products 

 of uranium are helium and an isotope 

 of lead. The rate of this transformation 

 is known, and data for calculating the age 

 of the mineral and with it the rock formation 

 of which it is a part, can be obtained by 

 measuring the quantities of helium and 

 lead in the rock and comparing them with 

 a quantity of uranium in the same volume 

 of material. Helium, however, is a gas, 

 and probably a portion of it leaks out. 

 Consequently, estimates of age on the basis 

 of helium ratios should be regarded as 

 minimum. But estimates based on the 

 lead ratios, when the mineral is fresh and 

 primary, offer results that carry great 

 weight as reliable indicators of age. 



Up to the present time, the highest 

 reliable lead ratio indicates the passage of 

 1,460,000,000 years. This has been com- 

 puted from the Keystone uraninite of the 

 Black Hills, South Dakota, the most 

 ancient uraninite yet discovered. Its age, 

 however, does not represent the maximum 

 age of the earth, as the mineral occurs in 

 a pegmatite dike which is intrusive into a 

 still older rock. What the age of the older 

 rock is, cannot be estimated from the 

 available geological data. All that can be 

 stated definitely now is that the age of the 

 earth far exceeds 1,460,000,000 years. 



Material from Utah Cliff-Houses 



An unusual and excellent collection of 

 archaeological material from clifl-houses of 

 Utah has been installed in Hall 7. It comes 

 from clifl-houses built about a.d. 900-1300. 

 The exhibit includes crutches, a cane, bas- 

 kets, beans, squash seeds, raw cotton and 

 cotton products, yucca sandals, cordage, 

 cradles, agricultural implements, a bow-drill, 

 and a wooden head rest. The remarkable 

 preservation of these perishable articles is 

 due to the extreme and permanent aridity 

 of the large caves in which they were buried. 



"Three Kingdoms of Indo-China" 



An excellent account of the journeys into 

 remote places and the adventures experienced 

 by members of the William V. Kelley- 

 Roosevelts Expedition to Eastern Asia for 

 Field Museum is to be found in a book. 

 Three Kingdoms of Indo-China, recently 

 published. The authors are Harold J. 

 Coolidge, Jr., leader of the Indo-Chinese 

 division of the expedition, and Colonel 

 Theodore Roosevelt, who was one of the 

 leaders of the expedition as a whole. The 

 book is written in popular style, giving to 

 the lay reader a clear idea of how a large 

 scientific expedition conducts its work, and 

 the many difficulties and problems that 

 beset it. The book is copiously illustrated 

 with photographs taken by the explorers. 

 The "Thomas Y. Crowell Company is the 

 publisher. 



For purposes of comparison, an exhibit 

 of specimens of fossil and modern forms of 

 life of similar species is on view in Stanley 

 Field Hall. 



HOPI DOLLS 



By Paitl S. Martin 

 Assistant Curator of North American Archaeology 



A case of Hopi dolls or katcinas has been 

 placed on exhibition in Hall 7. These dolls 

 are carefully made so as to show in miniature 

 the headdresses, symbolic masks, orna- 

 ments, and clothing worn by the masked 

 dancers who impersonate supernatural be- 

 ings or katcinas. Such figures are never 

 worshiped and are not idols in any sense. 

 At the conclusion of one of the great 

 rain-making ceremonies, the masked dancers 

 run through the 

 village streets, dis- 

 tributing dolls like 

 these and other 

 presents to the 

 young children. 



The reason for 

 impersonating the 

 supernatural beings 

 is explained in the 

 following Hopi 

 legend: 



Long ago, the 

 gods or katcinas 

 used to live with 

 the people and 

 teach them how to 

 hunt, plant seeds, 

 make pottery and 

 baskets, and build 

 houses of stone. 

 After a time they 

 became displeased 

 with the people and 

 withdrew from the 

 villages to the high 

 mountains. Then 

 no rain fell, the 

 fields became dry 

 and thirsty, and 

 desolation and 

 misery spread over 

 the land. After the 

 people had suffered a long time, the gods 

 relented somewhat and told them that they 

 might wear masks and costumes to repre- 

 sent the gods who had formerly dwelt with 

 them, and that they might dance the 

 katcina dances which bring the rain. If all 

 instructions were honorably carried out, the 

 katcina would "possess" the dancers and 

 rain would surely fall. 



So now, every year, with great faith- 

 fulness, the Indians wear costumes and 

 masks to represent the gods and dance 

 their dances so that rain will fall and the 

 harvest will be bountiful. 



Hopi Doll 



On the headdress are rep- 

 resentations of ears of maize. 



Rare Book Presented to Library 



A monumental work of the greatest rarity 

 has just been presented to the Museum 

 Library from the estate of John B. Lord 

 by Mrs. Robert E. Ross, Mrs. Joseph H. 

 King, and Mrs. William E. Pratt. It is 

 the catalogue of the famous collection of 

 Oriental porcelains of William T. Walters 

 in Baltimore, and was published in 1897. 

 It consists of ten superbly bound volumes 

 (17 X 23 inches), arranged in five portfolios, 

 and containing 116 exquisite plates in colors 

 and more than 400 reproductions in black 

 and white. The text, written by S. W. 

 Bushell, has been reprinted in a handy 

 octavo volume. The edition was limited to 

 500 copies, most of which were distributed 

 among the subscribers. The work has been 

 out of print for more than twenty years. 



Fishes of Florida and other Gulf Coast 

 waters are represented in an exhibit in 

 Albert W. Harris Hall. 



