Title: Hearts of Oak.   
Subject(s): EXODUS to Arthur (Book)
Source: Sky & Telescope, Dec99, Vol. 98 Issue 6, p79, 3p, 3c
Author(s): Steel, Duncan
Abstract: Reviews the book `Exodus to Arthur: Catastrophic Encounters
with the Comets,' by Mike Baillie.
AN: 2421797
ISSN: 0037-6604
Note: Tucson-Pima Public Library subscribes to this magazine.
Database: MasterFILE Elite

Section: books and beyond

HEARTS OF OAK

Exodus to Arthur: Catastrophic Encounters with Comets Mike Baillie
(Chrysalis Books Ltd., 1999). 256 pages. ISBN 0-7134-8352-0. $19.95.

AS A SCHOOLBOY I LEARNED A SONG dating from when Lord Nelson ruled the
waves for Britannia.

The chorus began:

Heart of oak are our ships Jolly tars are our men.

The song lives on in the Steel household, as I rouse my own jolly tars
(sons aged 6 and 4, known to asteroid watchers as 5263 Arrius and 6828
Elbsteel).

What has this to do with the book now under review? Well, the text
largely concerns the hearts of oaks found in the British Isles and the
light they throw upon changes in Earth's cosmic environment throughout
the past several millenniums -- at least as interpreted from a
heterodox British/Irish viewpoint.

Mike Baillie is a professor of paleoecology at Queen's University,
Belfast. He should not be confused with Mark Bailey, Director of the
Armagh Observatory, only 60 kilometers away, an authority on cometary
dynamics who will enter this story again below. Baillie is an
acknowledged expert on dendrochronology, the study of tree rings and
what they can tell us about the changing ancient climates in which
those trees grew.

It should not be a surprise that tree rings have the capacity to
inform us on matters astronomical. The science of dendrochronology was
pioneered by Andrew Douglass, working in Arizona in the early part of
the 20th century. The University of Arizona continues as a major
center of excellence in this area of study, with allied subjects
having sprung from it (such as archaeological dating). At one stage in
his career Baillie considered moving to Tucson but decided to remain
in his native Belfast. Just as well, because the mighty oaks he has
examined have been preserved in Irish peat bogs, and there are few
swamps in the Sonoran Desert.

While he was later hailed as a visionary, the early ideas of Douglass
were greeted with less than instant acclaim. For example, he
maintained that tree rings showed the 11-year solar cycle in normal
times as well as abnormal events, such as the Maunder Minimum of
sunspots in the 17th century. Perhaps Baillie's suggestions will be
treated likewise. But I think that, in broad stroke, he is on the
correct track.

Some time ago Baillie came to the conclusion that tree rings indicate
a severe widespread disruption of the climate around A.D. 540, a
phenomenon evidenced by other events, such as the Justinian plague of
the Eastern Roman Empire. As has been the norm, an endogenous cause
was sought, the favorite being a massive volcanic eruption. For
Ireland, great Icelandic eruptions have been shown to deposit tephra
(glassy dust) layers in the bogs, and for some time Baillie championed
this concept.

But Baillie is open to new ideas, and in 1980 he noted, along with
much of the rest of the scientific world, the evidence from Luis
Alvarez and his team for an asteroid or comet impact having caused the
Cretaceous-Tertiary boundary event 65 million years ago (when the
dinosaurs died out). In this picture the Earth is not isolated from
the cosmos, and the environment can be perturbed (to say the least) by
exogenous agents.

Living in the United Kingdom, however, Baillie was also exposed to an
alternative history of asteroid/comet-driven extinctions. In 1979 Bill
Napier and Victor Clube -- then both at the Royal Observatory,
Edinburgh -- published in Nature a broader hypothesis of impact-caused
extinction than the specific concept of the Alvarez group. Note,
though, that the idea of impact-driven catastrophes has a much longer
history, dating back to at least Edmond Halley and William Whiston
three centuries ago. Lord Byron spoke of cometary calamities in 1821.
After Earth-crossing asteroids were discovered in 1932, the great
American meteoriticist Harvey H. Nininger wrote of their significance,
as did Fletcher Watson and Ralph Baldwin in terms of the origin of
lunar craters. In 1958 Ernst J. Opik, of Armagh Observatory, wrote of
the hazard that asteroids pose, and today his grandson (a member of
the British Parliament) is trying to push the U.K. government into
playing a significant part in the international Spaceguard effort.

The Napier and Clube impact hypothesis of two decades back involved
terrestrial catastrophism on time scales of tens of millions of years,
linked to the oscillations of the Sun about the plane of the Milky
Way. A quite different aspect of their work has been the idea that a
giant comet has gradually disintegrated in the inner solar system over
the past 10 or 20 millenniums, causing periodic bombardments of the
Earth by a stream of debris, affecting our climate. In this work they
have been joined by Mark E. Bailey, David J. Asher, and me, all of
whom either are or have been associated with Armagh at some stage. The
group was labeled the Cavaliers by Gerrit L. Verschuur in his book
Impact! (S&T: January 1997, page 64).

This coterie of astronomers, then, was close at hand to feed Baillie
alternative ideas for the origin of the A.D. 540 climatic downturn
that he felt sure he had identified (an important era, when
Christianity was spreading through Ireland). Eventually Baillie became
pretty much convinced that he should abandon his previously favored
volcanic thesis.

Baillie explains the background in the opening third of the book and
then embarks upon an explication of his new hypothesis. He is honest;
he writes that "the reader is about to embark on a journey which will
stretch credulity but which is entirely based on documentary sources
and a few logical jumps"

Actually his interpretation of the evidence is more closely aligned
with the suggestion published by Fred Hoyle and N. Chandra
Wickramasinghe in 1978 that the dinosaur extinction was due not to a
cometary impact but rather to a close call. The logic is impeccable.
The Earth is a tiny target, so for every strike there are thousands of
close approaches. For asteroids, only impacts count. But for comets, a
flyby results in our planet passing through the cometary coma, which
can be larger than the Moon's orbit. In such an event, we would
accumulate a mass of dust, which takes years to settle out of the
atmosphere. These crossings must occur on millennial time scales.
(Napier and Wickramasinghe are currently investigating the climatic
effects.)

Baillie suggests that the A.D. 540 climatic disruption was due to a
dust veil being lowered over the planet, and he adduces much evidence
in support of the idea: not only physical evidence from tree rings and
the like, but also from the written accounts and mythology of
disparate civilizations.

Was the A.D. 540 event the sole such episode in recent times? Baillie
thinks otherwise. He also explores other epochs. Bronze Age
specialists know that something strange happened around 2345 B.C., and
Baillie discusses the evidence. Similarly in 1628 and 1159 B.C. he
finds that the Irish oaks preserved in their bogs tell a story of
exceptional cooling, at the same time as Egyptian and Chinese (and
indeed Irish) annals speak of interesting times in the sky.

If these climatic excursions were due to veiling events resulting from
cometary dust, then should we not find layers of such material in
suitable reservoirs? As Baillie explains, the ice-pack evidence is
equivocal. Just five weeks back I visited Belfast to discuss with
Baillie, Valerie Hall, and other members of the team their plans to
search for cosmic dust in the Irish peat bogs themselves. A positive
result might mean that the bogs have exhibited both the cause and the
effect of these environmental deviations.

The book is not without fault. If Baillie had seen fit to coin
abbreviations for "dendrochronology" and "dendrochronologist" then the
text would have been 10 pages shorter, and fewer trees would have been
chopped down to print it. The comet associated with Julius Caesar
actually appeared months after his assassination. James Ussher (who
came up with 4004 B.C. as the beginning of the universe) was
Archbishop of Armagh and Primate of All Ireland, so it is especially
incongruous that Baillie spells Ussher's name incorrectly.

Nevertheless, Exodus to Arthur is a valuable addition to the
literature. For those enthusiasts of astronomy who would like to
discover more about how their science may have affected the
development of human civilizations, it is a highly recommended read.
Baillie is not scared of being wrong. But he may well be right.

For some years DUNCAN STEEL directed an asteroid and comet search and
tracking program in Australia, resulting in his book Rogue Asteroids
and Doomsday Comets (Wiley, 1995). He has recently moved back to the
United Kingdom to start a space-research program at the University of
Salford.

PHOTO (COLOR): What hath comets wrought? According to Exodus to
Arthur, ...

What hath comets wrought? According to Exodus to Arthur, perhaps ice
ages and the Dark Ages. Comet Tago-Sato-Kosaka (C/1969 T1) passed
safely by 30 years ago.

PHOTO (COLOR): Climatic digressions are preserved in trees from an
Irish ...

Climatic digressions are preserved in trees from an Irish bog. The
narrow rings seen in this slice signal harsher weather in 2354 to 2345
B.C., perhaps caused by the dusty wake of a comet that passed a little
too close to Earth. Courtesy Mike Baillie.

~~~~~~~~

Review by Duncan Steel
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Source: Sky & Telescope, Dec99, Vol. 98 Issue 6, p79, 3p, 3c.
Item Number: 2421797
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