Title: Dusk of the dinosaurs.
Subject(s): T. Rex & the Crater of Doom (Book); GREAT Dinosaur
Extinction Controversy, The (Book)
Source: Scientific American, Sep97, Vol. 277 Issue 3, p95, 3p, 1c
Author(s): Benton, Michael J.
Abstract: Reviews the books `T. Rex and the Crater of Doom,' by Walter
Alvarez, and `The Great Dinosaur Extinction Controversy,' by Charles
Officer and Jake Page.
AN: 9709243680
ISSN: 0036-8733
Note: Tucson-Pima Public Library subscribes to this magazine.
Database: MasterFILE Elite

Section: REVIEWS AND COMMENTARIES

DUSK OF THE DINOSAURS

T. Rex and the Crater of Doom

BY WALTER ALVAREZ, Princeton University Press, Princeton, N.J., 1997
($24.95)

The Great Dinosaur Extinction Controversy

BY CHARLES OFFICER AND JAKE PAGE, Addison-Wesley, Reading, Mass., 1996
($25)

The extinction of the dinosaurs is one of the great mysteries of
evolution, and scientific sleuths are not shy about reconstructing the
crime. "A world first dark and frozen, then deadly hot, a world
poisoned by acid and soot. This was the global aftermath of the
Yucatan impact," Walter Alvarez writes, advancing his theory that an
asteroid brought about the dinosaurs' demise. Meanwhile Charles
Officer and Jake Page assert: "The Alvarez hypothesis has collapsed
under the weight of accumulated geologic and other evidence to the
contrary, as well as from an increasingly obvious absence of
scientific evidence proffered in its support." How can leading
scientists who have been involved in this debate for nearly 20 years
arrive at such different conclusions?

The story effectively began in 1980,when Luis W. Alvarez (Walter's
father) and his colleagues published a paper in Science asserting that
a 10-kilometer-wide asteroid hit the earth 65 million years ago. The
impact, they contended, threw up a global dust cloud that blacked out
the sun, halted plant photosynthesis and triggered a wave of
extinction. With their food gone, the herbivores died out; the
carnivores then followed. This simple model was built on limited
observational support and was, needless to say, highly controversial.

The main piece of evidence supporting the Alvarez scenario was the now
famous "iridium spike." Concentrations of iridium, normally around 0.1
to 0.3 part per billion, shot up to nine parts per billion in
sediments from the time of the dinosaur extinction (known as the
Cretaceous-Tertiary, or K-T, boundary). On the earth, iridium comes
almost exclusively from space--specifically, from meteorites. The low
background levels derive from the numerous minor impacts that occur
all the time. Alvarez proposed that the spike indicated an unusually
high rate of iridium deposition on the earth and, hence, a huge
impact. The 1980 Science paper attracted instant and massive press
coverage.

Walter Alvarez tells the story leading up to the 1980 paper, and the
events since then, in an engaging and witty manner. Although much of
the tale is common knowledge, he offers new insights into the
published and unpublished stages of the debate. Most geologists and
paleontologists initially objected to the Alvarez theory. They argued,
first, that dinosaurs and other groups died out gradually (over at
least a million years) rather than instantaneously; second, that the
iridium layer was a local feature that represented some minor
peculiarity in the sediments; third, that Alvarez and his crew were a
bunch of physicists and chemists who should stick to their own patch;
and fourth, that the whole notion was pitched at the press and had no
scientific basis. From the start, the debate mixed science and
personalities, hype and hypotheses.

Officer and Page, who began as skeptics of the Alvarez hypothesis and
never wavered, thread their book with some wonderful gossip,
backbiting and accounts of scurrilous deeds by impact proponents. They
report extensive evidence for bias in reporting and funding of the
pro- and anti-impact viewpoints. They are uncomfortable with the
perceived pecking order in science: math and physics good, chemistry a
form of physics and so acceptable, biology and geology pretty dodgy,
psychology and geography beneath contempt. The authors characterize
Luis Alvarez as little more than the devil incarnate, one of the most
extraordinary character assassinations of a recently deceased person
that I have ever read.

But what of the science? The 1980 Science paper cited iridium spikes
from two locales. Such enhancements have now been found at more than
200 sites all over the earth, in sediments deposited in shallow and
deep seas, in rivers and on land. The iridium is frequently associated
with small, glassy beads (the results of melting) and shocked quartz
and stishovite (the results of high pressures)--pieces of confirming
evidence that were not even predicted in 1980. Searchers found the
Chicxulub crater in Mexico in 1991. This 150-kilometer-wide depression
is surrounded by thick deposits of ejecta and by deposits around the
shores of the proto-Caribbean that show the effects of tsunamis set
off by the impact.

Alvarez does not dismiss all contrary evidence and allows some role
for volcanism in the mass extinction. He is also honest in telling of
the dead ends that he and his colleagues pursued, such as the failed
attempt to use beryllium 10 to calculate rates of sedimentation and
studies of the Manson crater in Iowa (an early candidate for the K-T
impact but too small). T. Rex and the Crater of Doom is strongest in
presenting the evidence for the impact and its immediate physical
effects but rather weaker in explaining just how the dust clouds,
darkness, freezing, tidal waves and other environmental challenges
actually killed the dinosaurs.

Officer and Page have taken on the task of presenting a cohesive
opposition to the prevailing impact hypothesis. They have made things
much more difficult for themselves, however, by seeking not only to
deny the impact extinction model but also to deny the existence of the
impact as well. As a result, they fail miserably. They spend most of
the book attempting to show that the geologic evidence--the iridium
spike, shocked quartz, glassy spherules and other phenomena--points to
volcanism. To do so, the authors make selective use of the literature.
As they observe, Hawaiian-type volcanoes may emit iridium, some
volcanoes produce glassy melt spherules, and certain high-pressure
eruptions may give rise to a kind of shocked quartz. But no known
volcano, ancient or modern, produces all these materials together,
with the peculiar characteristics seen at the K-T boundary.

Presentation of the paleontological data should have been a strength
of Officer and Page's book. Here the evidence is fairly equally
balanced: there are signs that some groups of organisms died out
instantaneously, whereas others seem to have become extinct over spans
of five to 10 million years. I was staggered to see that The Great
Dinosaur Extinction Controversy treats the fossil record in only a few
pages of mostly obsolete and sometimes misleading data. For example,
Officer and Page represent the decline of ammonites by illustrations
from papers published in 1969 and 1991. The latter diagram, by Peter
Ward of the University of Washington, is said to show a gradual
decline of ammonites, even though Ward himself interprets it as
evidence of patchy collecting. The authors' account of the dinosaurs'
disappearance is vague in the extreme and takes little account of
extensive research work since 1970. Moreover, the two do not mention
at all the recent large-scale studies of dinosaur decline through the
Hell Creek Beds in Montana.

At the very least, Officer and Page develop their alternative to the
impact model fairly well. They outline recent work on what might have
been the long-term environmental effects of the events that gave rise
to the Deccan Traps, enormous outpourings of lava that occurred at the
end of the Cretaceous in what is now India. Without a strong
paleontological underpinning, however, this argument falls a little
flat. Officer and Page cannot make precise links between environmental
crises during the past 10 million years of the Cretaceous and specific
phases of the extinction.

These shortcomings are unfortunate, because the impact hypothesis
still has significant holes in it. The reality of the K-T impact is
now essentially undeniable. How else to explain the iridium layer, the
shocked quartz, the stishovite and, above all, the gigantic Chicxulub
crater? Yet I cannot see how a single impact could produce such a
complex extinction event as the one at the K-T boundary. Furthermore,
there is almost no evidence linking an impact to any of the other mass
extinctions. Equally, there have been a number of well-dated large
impacts, such as the Manicouagan event in British Columbia, that
caused no extinctions at all.

Read Alvarez first, for an excellent account of the pro-impact
position and for insight into how scientists pose questions and seek
to resolve them by sometimes roundabout means. Read Officer and Page
as a spicy account of the politics of science. But bear in mind that
whether or not they are right about Luis Alvarez's character, even
abrasive scientists may have the right ideas.

PHOTO (COLOR): DINOSAURS were a diverse group, adding to the mystery
of their extinction.

~~~~~~~~

Review by Michael J. Benton

MICHAEL J. BENTON is a paleontologist in the department of geology at
the University of Bristol.