A. E. (Andrew Ellicott) Douglass (July 5, 1867, Windsor, Vermont – March
20, 1962, Tucson, Arizona) was an American astronomer. He discovered a
correlation between tree rings and the sunspot cycle.
"Douglass
tracked this into past centuries by studying beams from old buildings as
well as Sequoias and other long-lived trees. Noting that tree rings were
thinner in dry years, he reported climate effects from solar variations,
particularly in connection with the 17th-century dearth of sunspots that
Herschel and others had noticed. Other scientists, however, found good
reason to doubt that tree rings could reveal anything beyond random
regional variations. The value of tree rings for climate study was not
solidly established until the 1960s."
Douglass founded the discipline of dendrochronology, which is a method
of dating wood by analyzing the growth ring pattern. He started his
discoveries in this field in 1894 when he was working at the Lowell
Observatory. During this time he was an assistant to Percival Lowell and
William Henry Pickering, but had a falling-out with them, when his
experiments made him doubt the existence of artificial "canals" on Mars
and visible cusps on Venus. Craters on the Moon and Mars are named in
his honour.
In 1909, Clark Wissler, of the American Museum of Natural History,
organized the Archer M. Huntington Survey. One objective of this survey
was to determine temporal arrangement of the American Southwest’s
prehistoric ruins. Wissler, who had read about Douglass’s work
concerning the relationship between precipitation and tree growth, later
contacted Douglass saying:
Your work suggests to me a possible help in the archaeological
investigation of the Southwest…We do not know how old these ruins are,
but I should be glad to have an opinion from you as to whether it might
be possible to connect up with your modern and dated trees specimens
[with wood specimens] from these [prehistoric] ruins by correlating the
curves of growth…I shall be glad to hear from you as to whether you
think it is possible for us to secure any chronological data from the
examination of this material.
On June 19, 1914, the curator of the American Museum of Natural History
wrote a letter to Douglass expressing his desire to begin archaeological
analysis as early as possible.
In 1916, Douglass began obtaining and analyzing archaeological samples
first collected during an expedition to northwest New Mexico by the
University of Colorado and the American Museum of Natural History. In
April 1918, Wissler asked Douglass whether or not it would be possible
to assign relative dates to samples that couldn’t be dated absolutely.
Although this information would not associate particular sites with
exact years, it would reveal whether or not ruins were constructed
within the same time period. On May 22, 1919, Douglass informed Wissler
that six specimens from Aztec Ruin, New Mexico were cut down within a
two year period, and estimated that samples from Pueblo Bonito in New
Mexico were possibly 25 years older than those collected at Aztec Ruin.
Upon receiving this news, Wissler was certain that Douglass would make a
crucial contribution to archaeology. Douglass continued comparing
samples between the two sites and concluded Pueblo Bonito actually
predated Aztec Ruin by 40 to 45 years. These findings led to realization
that relative dating could be used on many of the other ruins in the
Southwest. Although promising steps had been made in solving the mystery
of the ruins in the Southwest, in 1920, the American Museum of Natural
History discontinued the funding of Douglass’s research. In order to
continue his dendroarchaeological research, Douglass would have to find
funding elsewhere.
On January 22, 1922, Douglass was informed that the National Geographic
Society could be a potential source of funding. By May of that year, the
idea of a Beam Expedition funded by the National Geographic Society was
conceived. Beam Expeditions, funded by the National Geographic Society
took place in 1923 and 1928. These expeditions produced a floating
chronology of 585 years for Southwestern ruins, and extended Douglass’s
Flagstaff chronology of Ponderosa Pine, which was 500 years long in
1914, to A.D. 1260. However, these expeditions failed to bridge the gap
that existed between these two chronologies.
In 1929, Douglass set out on a third Beam Expedition. This expedition
explicitly targeted samples that would potentially bridge the gap
between the two chronologies. Finally, on June 22, 1929, a beam labeled
HH-39 was extracted at the Show Low site in Arizona. This beam took the
Flagstaff chronology back to A. D. 1237. Later that day, the inner rings
of HH-39 were successfully crossdated against the outer rings of
Douglass’s floating chronology. Over 15 years after he began working
with Clark Wissler, Douglass had bridged the gap and, as a result, had a
continuous record of tree-ring data dating back to A. D. 700. For the
first time in history, dates could be assigned to Southwestern ruins
with certainty. Cliff dwelling at Tsegi Canyon, Mesa Verde, and Canyon
de Chelly dated back to the 13th century. It was determined that Aztec
Ruin was constructed during a period ranging from A. D. 1111-A. D. 1120.
Pueblo Bonito was found to be built in the latter portion of the 11th
century.
Douglass formally reported his findings in the December 1929 issue of
National Geographic. He wrote:
Its inner rings overlapped the late decades of the old chronology by 49
years, the final ring resting on the year 537 of that sequence; its
outer ones overlapped the earliest 120 years of the new, the last one
reaching to 1380. Thus the 26 years from 1260 to 1286, which belonged to
both chronologies, were definitely matched and their union confirmed by
HH-39, which in American archaeology is destined to hold a place
comparable to Egypt’s Rosetta Stone…With careful archaeological study we
shall perhaps be able to trace the movement of clans and test tribal
traditions which have been so often quoted as the early history of these
people.
Emil Haury, one of the men who helped extract HH-39, stated:
For the three of us [Emil W. Haury, Lyndon L. Hargrave, and Neil M.
Judd], the experience was unforgettable. To be present at the instance
of the celebrated breakthrough in science that set the chronological
house in order for the Southwestern United States was reward enough. But
beyond that, was the privilege to work for a time at the side of
Douglass, the scholar, the astronomer turned archaeologist.
Douglass returned to the University of Arizona where he became the first
person to formally teach classes in dendrochronology. In 1937, the
science continued to develop when Douglass established the Laboratory of
Tree-Ring Research at the University of Arizona.
Since Douglass’s famous discovery in the American Southwest, his
dendroarchaeological techniques have been used to date structures around
the world. Furthermore, dendrochronology has been applied in a number of
ways. Currently, tree rings are being used to reconstruct an array of
activity including: fire regimes, volcanic activity, hurricane activity,
glacial movement, precipitation, mass movements, and hydrology. In many
ways anthropologists, ecologists, geographers, and geologists are able
to analyze the past and predict future trends. All of this is possible
thanks to the archaeological achievement of A.E. Douglass.
Anecdote:
Dr Douglass's home shared a party line with his neighbours, whose
teenage daughter, as she was then, enjoyed long phone calls with her
friends. A.E. would rattle the cradle to indicate that he required
access to the line, only to be ignored. He was not blessed pleased. She
contributed: We were in awe of him because we knew of his research and
enamoured of his huge tree ring specimen which eventually was displayed
at the University of Arizona Museum.
|
