Date sent: Thu, 24 Apr 1997 13:20:08 -0400 (EDT)
Priority: NORMAL

From: New Scientist vol. 154, No 2079, 26 April 1997


Did comet power spark life on Earth? Researchers in
California are suggesting that comets might not only have
provided the starting material, but could also have
supplied the energetic push that got biological chemistry

About 4 billion years ago, comet impacts were a thousand
times as frequent as they are now. Comets are made up of
volatile ices and carbon compounds, which at first glance
seem the perfect ingredients to get life's chemistry

However, comets must have reached temperatures of more than
10.000 degree C as they burnt up in the atmosphere. "They
were coming in so fast and so hot that any decently sized
molecule got blown to smithereens," says Chris McKay, a
geochemist at NASA Ames Research Center in Moffett Field,

Despite this, McKay has shown that the comets may have been
the source of complex molecules after all. He calculated
that if a comet's molecules broke up into elements at high
temperatures, they would recombine as they cooled to leave
water, carbon dioxide, methane, nitrogene and hydrogen

What's more, says McKay, his team's experiments suggest
that subsequent impacts might have provided the energy to
transform these compounds into more complex ones. The
researchers took a jar filled with the comet gases, and
focused a laser onto them to deliver a 30.000 degree C
pulse of heat. As they report in last week's SCIENCE (vol
276, p. 390), this created at least a dozen new compounds,
some with chains six carbon atoms long.

"Most people think of these impacts as bad and
destructive," says Norman Sleep of Stanford University in
California. "Here they show they can actually provide the
basic building blocks of life."

Philip Cohen, San Francisco


Date sent: Thu, 24 Apr 1997 13:06:26 -0400 (EDT)
Priority: NORMAL

Book Announcement:

P J Thomas, C F Chyba, C P McKay [eds]:
Berlin, Heidelberg, New York, London, Paris, Tokyo
Springer Verlag 1996
ISBN 0-387-94650-0

"When two great masses come into collision in space, it is
certain that a large part of each is melted, but is seems
also quite certain that in many cases a large quantity of
debris must be shot forth in all directions, much of which
may have experienced no greater violence than individual
pieces of rock experience in a landslip or in blasting by
gunpowder. Should the time when the earth comes into
collision with another body, comparable in dimensions to
itself, be when it is still clothed as at present with
vegetation, many great and small fragments carrying seeds
of living plants and animals would undoubtedly be scattered
through space. Hence, and because we all confidently
believe that there are at present, and have been from time
immemorial, many worlds of life besides our own, we must
regard it as probable in the highest degree that there are
countless seed-bearing meteoric stones moving about through
space. If at the present instant no life existed upon the
earth, one such stone falling upon it might, by what we
blindly call n a t u r a l causes, lead to its becoming
covered with vegetation."

This remarkable quote is taken from the presidential
address by William Thompson to the meeting of the British
Association which took place in London in '81.

Now, you might ask yourself what is so remarkable about
this quote? After all, quite a number of scientists have
speculated about the extraterrestrial origin of life during
the last two decades. Let me tell you then that William
Thompson (later Lord Kalvin) made his remarks more than 100
years ago, in 1881!

In fact, it took almost exactly 100 years before this
"ridiculous" idea became the communis opinio about the
origins of life on earth. Whilst COMETS & THE ORIGIN &
EVOLUTION OF LIFE does not address the question as to
w h y it took scholars that long to liberate science from
the straightjacket of uniformitarian evolution, it provides
an historical overview of the development of the extra-
terrestrial hypothesis in an interesting introductory paper
by J Oro and A Lazcano.

Like most new publications on neo-catastrophism and
cometary astronomy, this historical chapter unfortunately
distorts the real struggle, obstacles and outright
opposition this and related astronomical ideas had to face
during the 19th and 20th centuries. In many respects the
paper evokes the appearance of research normality and
continuity in the development of the extraterrestrial
impact concept. This "Whiggish" treatment of science
history (sometimes also called "presentism") reminds one of
Thomas Kuhn's famous complaint about the historian's method:
"Partly by selection and partly be distortion, the
scientists of earlier ages are implicitly represented as
having worked upon the same set of fixed problems and in
accordance with the same set of fixed canons that the most
recent revolution in scientific theory and method has made
seem scientific. No wonder that textbooks and the
historical tradition they imply have to be rewritten after
each scientific revolution. And no wonder that, as they are
rewritten, science once again comes to seem largely

One only has to recall the opposition to Fred Hoyle's and
Chandra Wickramasinghe's theories (not to mention earlier
advocates of "Panspermia") to realise that science never
progresses as smoothly as is claimed in most textbooks.

comprehensive information about the current state of
knowledge and research regarding the cometary origin of
many features of our planet such as organic molecules,
water, the atmosphere and the oceans. In addition, it
assesses the affects of major impacts on the evolution of
life and the biosphere. That impact catastrophes inevitably
had a dramatic affect in this respect is clear. Mass
extinctions are certainly the most obvious and researched
consequences of significant impact events. Yet exactly how
such catastrophes might also have led to evolutionary
mutations and sudden changes in both the animal kingdom and
human evolution is not addressed in this volume.

Comets and asteroids, the editors point out, have always
had a dual role in the history of the earth: "they were
both deliverers of organic material and volatiles, and also
destroyers of organic material, by the heat and shock of
violent impact." The idea that primitive forms of "life" on
earth originated from space (rather than being homegrown)
has become the new paradigm of evolutionary theory. That's
the good news. The bad news is that - despite the title -
the book does not really address the origin (let alone
evolution) of life. By focusing on how it may have arrived
on our planet, it has simply shifted (both cosmologically
and intellectually) the age-old and more complex question
as to the real "creation" of life out of "nothing". But
then you cannot expect to get all your questions solved for
a mere 25 Sterling.

Benny J Peiser



PJ Thomas, CF Chyba, CP McKay: Introduction: Comets and the
Origin of Life

J Oro & A Lazcano: Comets and the Origin and Evolution of

A Delsemme: The Origin of the Atmosphere and of the Oceans

J Kissel, FR Krueger, K Roessler: Organic Chemistry in
Comets from remote and in situ Observations

WF Huebner & DC Boice: Polymers and other Macromolecules in

PJ Thomas & L Brookshaw: Numerical Models of Comet and
Asteroid Impacts

CF Chyba and C Sagan: Comets as a Source of Prebiotic
Organic Molecules for the Early Earth

KJ Zahnle & NH Sleep: Impacts and the Early Evolution of

D Steel: Cometary Impacts on the Biosphere

D Morrison: The Contemporary Hazard of Cometary Impacts

M Podolka & D Prialnik: 26Al and Liquid Water Environments
in Comets

CP McKay: Life in Comets

CP McKay: Comets and Space Missions

CCCMENU CCC for 1997