ScienceWeek

SCIENCE-WEEK

A Weekly Email Digest of the News of Science

A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy-makers.

March 16, 2001 -- Vol. 5 Number 11

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The fairest thing we can experience is the mysterious.
It is the fundamental emotion which stands at the cradle
of true science. He who knows it not, and can no longer
wonder, no longer feel amazement, is as good as dead.
We all had this priceless talent when we were young.
But as time goes by, many of us lose it. The true scientist
never loses the faculty of amazement. It is the essence
of his being.
-- Hans Selye (1907-1982)

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=-=-=-=-=-=-=-=-=
Section 1
=-=-=-=-=-=-=-=-=

Contents of this Issue (Full reports in Section 2):

1. ASTROBIOLOGY:
EXTRASOLAR JOVIAN PLANETS AND EXTRATERRESTRIAL LIFE
The most striking and oft-quoted characteristic of the extrasolar
planets thus far detected is the preponderance of Jovian-mass
planets at small orbital distances from their parent stars.
Although the apparent statistical overrepresentation of such
tight orbits in the cohort of planets is biased by the fact that
Doppler spectroscopy is most sensitive to smaller orbital semi-
major axes, the mere existence of such objects forces a
significant shift in our expectations regarding planetary system
architectures. By virtue of their strong gravitational pull,
giant planets define the dynamical and collisional environment
within which Earth-like planets form. The spatial location and
mass distribution of giant planets will predetermine the
existence and habitability of terrestrial planets. The presence
of giant planets scattered uniformly from 0.04 to 3 *astronomical
units (AU) has enormous implications for the frequency of 
habitable Earth-like planets in our Galaxy.
(Jonathan I. Lunine: Proc. Natl. Acad. Sci. US 30 Jan 01 98:809)

2. EXPERIMENTAL PHYSICS: ON DEFINING THE METER
Underlying all measurements of the speed of light is the
assumption that it has a unique and universal value that connects
space and time. Thus, of the three quantities, the meter, the
second, and (c) (the velocity of light), two can be defined
independently -- whichever two are most convenient. In the 1960s,
it became apparent that the meter was not convenient: one could
achieve higher precision in the measurement of length by defining
the speed of light to have a convenient value and letting the
meter be some fraction of the distance that light travels in one
second. Consequently, in 1983, the 17th General Conference on
Weights and Measures decreed that the velocity of light (c) is
exactly 299,792,458 meters per second. Thus, the meter is now a
derived unit, defined to be the distance light travels in 1/c
seconds. (Daniel Kleppner: Physics Today March 2001)

3. MATERIALS SCIENCE:
A NEW METHOD FOR PATTERNING OF THIN-FILM ELECTRETS
Researchers report a new method that uses a flexible
micropatterned electrode to pattern an electret thin film in a
parallel process by injecting and trapping charges over areas of
approximately 1 square centimeter. The method is called
"electrical microcontact printing". Because the electrode is
flexible, it can make sufficiently intimate electrical contact
with a solid surface to produce uniform pattern transfer by
charging. Areas as large as 1 square centimeter were patterned
with trapped charges at a resolution better than 150 nanometers
in less than 20 seconds. This process provides a new method for
patterning, and it suggests possible methods for high-density,
charge-based data storage and possible methods for high-
resolution charge-based printing.
(H.O. Jacobs and G.M. Whitesides: Science 2 Mar 01 291:1763)

4. NEUROBIOLOGY: THE STRUCTURE OF THE NEUROMUSCULAR JUNCTION
Researchers report the use of computerized serial angular
electron microscope imaging (electron microscope tomography) to
demonstrate the arrangement and associations of structural
components of active zone material in a model synapse, the frog
neuromuscular junction. On the basis of their observations, the
authors propose that the active zone material is a
multifunctional organelle that regulates a) the docking and
fusion of synaptic vesicles at, and with, the presynaptic
membrane; b) the anchoring of calcium channels in the membrane;
and c) the maintenance of spatial relationships between docked
vesicles and channels. The authors suggest the active zone
material is also likely to be involved in the adhesion of the
presynaptic membrane to the postsynaptic membrane via the
extracellular matrix of protein between the cells. The authors
suggest their general hypothesis should be testable at
neuromuscular junctions and other synapses.
(M.L. Harlow et al: Nature 25 Jan 01 409:479)

5. PALEONTOLOGY: ON THE SKULL OF THE MIGHTY ALLOSAUR
Researchers have applied computed tomography and finite element
analysis to the long skull of the carnivorous theropod dinosaur
Allosaurus fragilis. The authors report they have generated the
most geometrically complete and complex finite element analysis
model of the skull of any extinct or extant organism. They have
used the model to test the mechanical properties of the skull,
and to examine in a quantitative manner long-held hypotheses
concerning overall shape and function. The results provide
quantitative evidence to suggest that during attack or feeding,
Allosaurus generally used a high velocity impact of the skull
into its prey: An analog would be a person wielding a large and
heavy hatchet. Aided by sharp, recurved teeth and powerful neck
musculature driving the skull downwards and then imparting a
retractile force, portions of flesh were sliced, torn away and
swallowed.
(E.J. Rayfield et al: Nature 22 Feb 01 409:1033)

6. ORIGIN OF LIFE: THE HABITAT AND NATURE OF EARLY LIFE
Our planet is more than 4.5 billion years old. Massive
bombardment of the planet occurred in the first 500 to 700
million years, and the largest impacts would have been capable of
sterilizing the planet. Probably until 4 billion years ago or
later, occasional impacts might have heated the ocean over 100
degrees centigrade. Life on Earth dates from before approximately
3.8 billion years ago, and is likely to have experienced one or
more hot-ocean bottlenecks. Only organisms optimally living in
water at 80 to 110 degrees centigrade (hyperthermophile
organisms) would have survived. It is possible that early life
diversified near hydrothermal vents, but hypotheses that life
first occupied other pre-bottleneck habitats are tenable
(including transfer from Mars on ejecta from impacts there).
Early hyperthermophile life, probably near hydrothermal systems,
may have been non-photosynthetic, and many housekeeping proteins
and biochemical processes may have an original hydrothermal
heritage. (E.G. Nisbet and N.H. Sleep: Nature 22 Feb 01 409:1083)

7. IN FOCUS: ON ELEMENTARY PARTICLES IN PHYSICS

8. FROM THE SCIENCEWEEK ARCHIVE:
ON AMMONIA AND THE POPULATION EXPLOSION

=-=-=-=-=-=-=-=-=
Section 2
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1. ASTROBIOLOGY:
EXTRASOLAR JOVIAN PLANETS AND EXTRATERRESTRIAL LIFE
     Since the discovery of a planet orbiting the star 51 Pegasi
in 1995, approximately 50 other planets have been detected
through their influence on the radial velocities of lines in the
spectra of their parent stars. The orbital motion of the planet
can be detected by perturbations of the motion of the parent star
("reflex motion"), and these perturbations can be measured using
high-precision spectroscopy. This indirect technique cannot
investigate the radius or composition of the planet, and can
place only a lower limit on the mass of the planet. Of the
planets detected so far, many are apparently massive planets
larger than Jupiter, but there is controversy concerning
categorizations of these planets.
... ... Jonathan I. Lunine (University of Arizona, US) presents
an analysis of current research on giant extrasolar planets, the
author making the following points:
     1) The author points out that during the past 5 years the
field of extrasolar giant planets has matured from a field which
questioned the existence of planets around other stars to a field
that is currently involved in comparative extrasolar planetology.
Over 50 nearby stars, all approximately similar to the Sun, have
apparent companions detected by radial velocity measurements, at
least one system apparently has multiple planets, and one planet
(HD209458b) can be directly detected as it transits its parent
star. These data have enabled meaningful statistics to be
accumulated on the frequency of planets around solar-type stars,
and have also allowed modeling to reveal the bulk density and
early history of one planet.
     2) The author points out that at the present time there is
no standard nomenclature concerning extrasolar planets. The
author takes the term "Jovian mass" to denote an object ranging
from 0.1 to 13 Jupiter-masses. The upper mass is the minimum mass
for deuterium fusion in stars, a convenient cut-off for planets.
The author uses the term "giant planets" to refer specifically to
bodies in the mass range 0.1 to 13 Jupiter-masses that are
primarily hydrogen-helium, with a greater or lesser admixture of
heavier elements. Such objects are like our own giant planets in
approximate composition. There is only one extrasolar planet that
can be assigned with confidence to be a "giant planet", because
we know its radius, and hence its bulk density and composition.
In our own planetary system, Uranus and Neptune barely qualify,
because they are so rich in heavy elements; some planetologists
call Uranus and Neptune "ice giants" to distinguish them from
Jupiter and Saturn.
     3) The author points out that the most striking and oft-
quoted characteristic of the extrasolar planets thus far detected
is the preponderance of Jovian-mass planets at small orbital
distances from their parent stars. Although the apparent
statistical overrepresentation of such tight orbits in the cohort
of planets is biased by the fact that *Doppler spectroscopy is
most sensitive to smaller orbital *semi-major axes, the mere
existence of such objects forces a significant shift in our
expectations regarding planetary system architectures. Leaving
aside the issue of whether giant planets could form in place at
small orbital distances or must migrate inward, the author
suggests that the presence of giant planets scattered uniformly
from 0.04 to 3 *astronomical units (AU) has enormous implications
for the frequency of habitable Earth-like planets in our Galaxy.
Two important questions are: a) What fraction of Sun-like (solar-
type) stars might be precluded from having Earth-like planets
through occupation of the habitable zone by giant planets? b) Do
the processes of giant planet formation and dynamical evolution
generally suppress or encourage the production of habitable
planets, in terms of planetary growth, supply of volatiles and
organic material to the habitable zone, and long-term collision
rates of *planetesimal debris with habitable planets?
     4) From his analysis of current observations, the author
suggests: "By virtue of their strong gravitational pull, giant
planets define the dynamical and collisional environment within
which *terrestrial [Earth-like] planets form. In our Solar
System, the position and timing of the formation of Jupiter
determined the amount and source of the volatiles from which
Earth's oceans and the source elements for life were derived...
The spatial location and mass distribution of giant planets will
predetermine the existence and habitability of terrestrial
planets."
-----------
Jonathan I. Lunine: The occurrence of Jovian planets and the
habitability of planetary systems.
(Proc. Natl. Acad. Sci. US 30 Jan 01 98:809)
QY: Jonathan I. Lunine: jlunine@lpl.arizona.edu
-----------
Text Notes:
... ... *Doppler spectroscopy: In general, the "Doppler effect"
is a lengthening of the wavelengths of electromagnetic radiation
from a source caused by the movement of the source away from the
observer, and a shortening of wavelengths as the source moves
towards the observer. In this context, "Doppler spectroscopy" is
an indirect method of detecting extrasolar planets. It is stellar
wobble that betrays the existence of an invisible orbiting
planet. The greater the wobble, the more massive the planet, and
the time to complete one wobble cycle is the orbital period of
the planet. The Doppler effect has been used to detect these
small stellar movements: As a star travels toward the observer,
the light waves are shortened toward the blue; conversely, as a
star moves away from Earth, the wavelengths are lengthened toward
the red. These Doppler shifts are extremely small. In our Solar
System, the Sun wobbles by only 12.5 meters per second because of
the presence of Jupiter; Saturn induces variations of 2.7 meters
per second on a longer time scale, and the effect of other
planets is substantially less. A reliable detection of this
wobble requires precision of 3 meters per second, which is
equivalent to detecting changes in the wavelengths of starlight
by 1 part in 10^(8). The periodic wobble of a star provides the
planet's orbital period, the orbital distance, and the mass of
the planet multiplied by the unknown parameter sin(i), where (i)
is the inclination of the planet's orbital plane to the line of
sight.
... ... *semi-major axes: Either of the equal line segments into
which the major axis of an ellipse is divided by the center of
symmetry.
... ... *astronomical units (AU): 1 AU = the mean distance from
the Sun to the Earth = approximately 93 million miles, and
exactly 149,597,870 kilometers.
... ... *planetesimal: Planetesimals are bodies with dimensions
of 10^(-3) to 10^(3) meters that are believed to form planets by
a process of accretion. The term "accretion" refers to an
aggregation, an increase in the mass of a body by the addition of
smaller bodies that collide and adhere to it, provided the
relative velocities are low enough for coalescence. As the mass
of the agglomerate increases, so does the rate of accretion, and
this accretion process is believed to generally occur in the form
of a disk. A stellar accretion disk is a swarm of dust grains
that evolve into planetesimals and then planets.
... ... *terrestrial: The author defines terrestrial planets as 
"those bodies made primarily of rock (including metals, such as
iron-nickel), with solid surfaces capable of holding volatiles in
liquid and gaseous (as well as solid) form."
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Mar01
For more information: http://scienceweek.com/swfr.htm

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2. EXPERIMENTAL PHYSICS: ON DEFINING THE METER
     Length is one of the fundamental measuring units of physics,
and the standardization of this unit has an interesting history.
Indeed, a history of length measurement provides a revealing
perspective on the general history of science.
     Although there is evidence that many early civilizations
devised standards and various tools of measurement, the Egyptian
"cubit" is generally recognized as having been the most widely
used standard of linear measurement in the ancient world. The
cubit was developed in approximately 3000 BC, and was based on
the length of the arm from the elbow to the extended fingertips.
This length was standardized by a royal "master cubit" of black
granite, against which all the "cubit sticks" in use in Egypt
were measured at regular intervals. The idea of maintaining a
standard of length, therefore, is at least 5000 years old. The
royal cubit measured 524 millimeters in current units and was
subdivided in a complicated manner. The accuracy of the cubit
sticks derived from this royal cubit are demonstrated by the
dimensions of the Great Pyramid of Giza: although thousands of
laborers built this edifice, the sides of the pyramid vary no
more than 0.05 percent from the mean length of 230.364 meters.
     After the ancient Egyptians, the Babylonian "kus", or
"Babylonian cubit", was adopted nearly everywhere in the Middle
East. The kus measured approximately 530 millimeters; the "shusi"
was defined as 1/30 of a kus and was equal to 17.5 millimeters;
the "Babylonian foot" was taken as 2/3 of a kus.
     After 1000 BC, commercial domination of the Mediterranean
passed into the hands of the Greeks first and then the Romans. A
basic Greek unit of length was the "finger" (19.3 millimeters);
16 fingers equaled 30 centimeters (a "foot"); 24 fingers equaled
one "Olympic cubit". The Greeks probably derived their measures
partly from the Egyptians and partly from the Babylonians. The
Romans, adopting the Greek system, subdivided the foot into 12
"ounces" ("unciae", later "inches"). The Romans made 5 feet equal
to one "pace", and 1000 of these made up the "Roman mile".
     Apparently completely independent of Middle Eastern and
Mediterranean measurement history, the Chinese developed a system
of their own. The Chinese system also used parts of the body as
sources of units. The two basic units of length, the "chih" and
"chang", were set at approximately 25 centimeters and 3 meters,
respectively. A noteworthy characteristic of the Chinese system
was the common use of decimal notation, evident in Chinese
decimal rulers dating back to the 6th century BC, long before any
decimal measurement notation was used in the West.
     Medieval Europe inherited the Roman system, with its Greek,
Babylonian, and Egyptian roots. This system soon became common in
Europe, with many linguistic and regional variations, with some
measuring elements borrowed from Scandinavia and from the Arabs,
and with original European contributions resulting from the needs
of medieval commerce. Charlemagne (747-814) tried to impose
uniformity at the beginning of the 9th century, but he failed.
Ultimately, the great trade fairs of the 12th and 13th centuries
enforced a rigid uniformity on merchants of all nationalities
within the fair grounds, and this had some effect on the
standardization of units. The "ell", for example, was the
universal measure for wool cloth, a trading staple of the Middle
Ages, and it was standardized at 2 feet 6 inches, measured
against an iron standard in the hands of the Keeper of the Fair.
The ell was accepted by all the great cloth-manufacturing cities
of northwestern Europe.
     In England, by the time of the Magna Carta (1215), abuses of
weights and measures were common, and within a few years a royal
ordinance defined a broad list of units and standards that
remained in force in England and its colonies for 600 years. A
standard "yard", "the Iron Yard of our Lord the King", was
prescribed for the realm, divided into the traditional 3 feet,
each of 12 inches, "neither more nor less". The inch was
subdivided into 3 "barleycorns". The "furlong" (a "furrow long")
was eventually standardized as an eighth of a mile.
     A most important historical event in the history of the
fundamental measuring units was the establishment of the metric
system by the leaders of the French Revolution. In April of 1790,
one of the foremost members of the French National Assembly,
Charles Talleyrand-Perigord (1754-1838), re-introduced the idea
of a standard metric system (an idea that had been discussed in
various forms for over a century), and this launched a debate
that resulted in a directive to the French Academy of Sciences to
prepare a report. After several months, the academy recommended
that the length of the meridian passing through Paris be
determined from the North Pole to the Equator, that 10^(-7) of
this distance be termed the "meter" and form the basis of a new
decimal linear system, and that a new unit of weight be derived
from the weight of a cubic meter of water. A list of prefixes for
decimal multiples and submultiples was proposed. The liter was
defined as the volume equivalent to the volume of a cube, each
side of which had a length of 10 centimeters. The meridian survey
proved more difficult than anticipated, but finally in June 1799
the metric system became a fact, with the motto for the system,
"For all people, for all time." In the scientific world, this
standardization brought about by the French Revolution endured
until the 20th century.
     The present International System of units (SI System) was
developed because the 18th century standards were not accurate to
the degree required by 20th century science. After lengthy
discussions in Paris, the birthplace of the metric system, in
October 1960, the 11th General Conference on Weights and Measures
formulated a new international system of units. This system was
further amended in 1983, and currently the length unit of the SI
system, the "meter", is defined as the distance traveled by light
in a vacuum in 1/299,792,458 second.
... ... Daniel Kleppner (Massachusetts Institute of Technology,
US) presents an essay on the meter as a standard unit, the author
making the following points:
     1) The author points out that after the meter was defined in
France at the end of the 18th century, several platinum bars were
put forward to embody this length. Subsequent meridian surveys
revealed inaccuracies, and in 1889 the 1st General Conference on
Weights and Measures redefined the meter to be the distance
between engraved lines on a platinum-iridium bar that would rest
in Sevres (FR). But already 2 years before that Albert A.
Michelson (1852-1931) had discovered how to measure distance to a
fraction of the wavelength of light, and his method was so
precise that in 1889 the meter was obsolete at the moment of its
redefinition.
     2) In spite of the superiority of Michelson's methods, the
meter-bar in Sevres remained the legal standard for 71 years.
Finally, in 1960, the meter was redefined to be a certain number
of wavelengths of a particularly sharp and stable spectral line,
the red line of krypton-86. That happened to be the very year
that the laser was invented, and lasers and laser spectroscopy
quickly rendered this new definition of the meter obsolete. The
meter, in fact, was soon demoted from a primary standard to the
inferior rank of a derived unit.
     3) The author points out that underlying all measurements of
the speed of light is the assumption that it has a unique and
universal value that connects space and time. Thus, of the three
quantities, the meter, the second, and (c) (the velocity of
light), two can be defined independently -- whichever two are
most convenient. It was apparent that the meter was not
convenient: one could achieve higher precision in the measurement
of length by defining the speed of light to have a convenient
value and letting the meter be some fraction of the distance that
light travels in one second. Consequently, in 1983, the 17th
General Conference on Weights and Measures decreed that the
velocity of light (c) is exactly 299,792,458 meters per second.
Thus, the meter is now a derived unit, defined to be the distance
light travels in 1/c seconds.
-----------
Daniel Kleppner: On the matter of the meter.
(Physics Today March 2001)
QY: Daniel Kleppner, Dept. of Physics, Massachusetts Institute of
Technology 617-253-1000.
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 16Mar01
For more information: http://scienceweek.com/swfr.htm

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

3. MATERIALS SCIENCE:
A NEW METHOD FOR PATTERNING OF THIN-FILM ELECTRETS
     The term "dielectric" refers to an insulating material or a
very poor conductor of electric current. When such materials are
placed in an electric field, little or no current flows because
of the absence of mobile electrons. Instead, an electric
polarization occurs.
     In this context, the term "polarization" refers to a small
relative shift of positive and negative electric charge in
opposite directions within a dielectric, the shift induced by an
electric field as the field distorts the negative clouds of
electrons around positive atomic nuclei in accordance with the
polarity of the field. The slight separation of charge is a
"polarization". In material whose molecules are permanently
polarized as a consequence of chemical structure (e.g., water
molecules), some of the polarization of the material under the
influence of an applied electric field involves molecules
rotating into alignment with the applied field.
     The term "electret" refers to a material that retains its
electric polarization after being subjected to a strong electric
field: charges within the material become permanently displaced
in accordance with the polarity of the field. One end of the
electret becomes positive and the other end becomes negative.
Electrets are usually prepared from certain waxes, plastics, and
ceramics, the individual molecules of which are permanently
polarized but randomly arranged before an electric field is
applied. Upon the application of a strong electric field (e.g., 1
million volts per meter), the field rotates the polar molecules
into an alignment that persists when the external field is
removed. Electrets can also be made by allowing a molten material
to solidify in a strong electric field. The behavior of electrets
is analogous to that of permanent magnets. An electret, for
example, lines up in an electric field according to the polarity
of the field; and like a permanent magnet, if an electret is cut
into two pieces, each piece is found to be permanently polarized
as an electret. First discovered in 1925, electrets have found
applications in electrostatic (condenser) microphones.
... ... H.O. Jacobs and G.M. Whitesides (Harvard University, US)
report a technique for submicron patterning of charge in thin-
film electrets, the authors making the following points:
     1) The authors point out that patterns of charge are used in
photocopiers (xerography) to develop images with 100 micron
resolution. Systems that write and read patterns of charge have
been explored extensively because of their potential in
rewritable digital data storage. Current procedures based on
scanning probes achieve a writing rate of 100 kilobits per second
at an areal density of 7 gigabits per square centimeter, and
achieve a resolution of 100 nanometers. Although this density is
approximately 140 times the areal density of optical compact
discs, the writing rate is slow: patterning an area of 1 square
centimeter requires 24 hours.
     2) The authors report a new method that uses a flexible
micropatterned electrode to pattern an electret thin film in a
parallel process by injecting and trapping charges over areas of
approximately 1 square centimeter. The authors call this method
"electrical microcontact printing". Because the electrode is
flexible, it can make sufficiently intimate electrical contact
with a solid surface to produce uniform pattern transfer by
charging. Areas as large as 1 square centimeter were patterned
with trapped charges at a resolution better than 150 nanometers
in less than 20 seconds. This process provides a new method for
patterning, and it suggests possible methods for high-density,
charge-based data storage and possible methods for high-
resolution charge-based printing.
     3) In the present method, a poly(dimethylsiloxane) stamp,
patterned in bas-relief and supporting an 80-nanometer-thick gold
film, is brought into contact with an 80-nanometer-thick film of
the electret poly(methylmethacrylate) supported on silicon doped
with negative charge (n-doped silicon). A voltage pulse between
the gold film and the silicon transfers charge at the contact
areas between the gold and the polymer electret.
-----------
H.O. Jacobs and G.M. Whitesides: Submicrometer patterning of
charge in thin-film electrets.
(Science 2 Mar 01 291:1763)
QY: Heiko Jacobs: hjacobs@gmwgroup.harvard.edu
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 16Mar01
For more information: http://scienceweek.com/swfr.htm

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

4. NEUROBIOLOGY: THE STRUCTURE OF THE NEUROMUSCULAR JUNCTION
     The junctions between nerve cells and between nerve cells
and muscle cells are called "synapses", and in general there are
two types: electrical synapses and chemical synapses. Electrical
synapses involve direct flow of electrical current from one
neuron to another, the current flowing through so-called "gap
junctions", which are specialized membrane channels that connect
the two cells. Chemical synapses, which are more common, involve
communication via the secretion of "neurotransmitter" substances:
chemical agents released by the presynaptic neuron produce
secondary current flow in the postsynaptic cell by activating
specific receptor molecules in the surface membrane of the
postsynaptic cell. The secretion of neurotransmitter is triggered
by voltage-gated calcium ion channels through which an inflow of
calcium ion into the presynaptic terminal occurs. The rise of
calcium concentration causes presynaptic organelles that store
neurotransmitters ("synaptic vesicles") to fuse with the
presynaptic plasma membrane and release their contents into the
space between the pre- and postsynaptic cells.
     That is the general scheme of chemical transmission, and it
is apparently true not only for many types of neuron-neuron
interactions, but also for interactions between nerve cells and
muscle cells, the latter interactions occurring at so-called
"neuromuscular junctions".
... ... M.L. Harlow et al (5 authors at Stanford University, US)
present a study of the micro-architecture of the neuromuscular
junction of the frog, the authors making the following points:
     1) The authors point out that at synapses throughout the
nervous system, one or more areas on the cytoplasmic surface of
the plasma membrane of presynaptic nerve cells are studded with
distinctive aggregates of proteins. The aggregates can only be
observed by electron microscopy, and they are viewed best in
sections from fixed plastic-embedded tissue, where they stain
with heavy metals. The protein aggregates are confined to the
portion of the presynaptic membrane that faces the narrow cleft
between the pre- and postsynaptic cells, and some of the numerous
synaptic vesicles of the presynaptic cell, vesicles that contain
neurotransmitter molecules, are "docked" at the membrane adjacent
to the vesicles. The protein aggregates are situated at the
active zones of the presynaptic membrane, the sites where initial
events in the rapid neurotransmitter-mediated signaling between
the pre- and postsynaptic cells occurs. Since their discovery in
1956, the protein aggregates have been referred to in a variety
of ways, including "membrane thickenings" and "presynaptic
projections", as well as "active zone material", the term used by
the authors.
     2) The authors report the use of computerized serial angular
electron microscope imaging (electron microscope tomography) to
demonstrate the arrangement and associations of structural
components of active zone material in a model synapse, the frog
neuromuscular junction. On the basis of their observations, the
authors propose that the active zone material is a
multifunctional organelle that regulates a) the docking and
fusion of synaptic vesicles at, and with, the presynaptic
membrane; b) the anchoring of calcium channels in the membrane;
and c) the maintenance of spatial relationships between docked
vesicles and channels. The authors suggest the active zone
material is also likely to be involved in the adhesion of the
presynaptic membrane to the postsynaptic membrane via the
extracellular matrix of protein between the cells. The authors
suggest their general hypothesis should be testable at
neuromuscular junctions and other synapses by combining electron
microscope tomography with established procedures for localizing
specific proteins, and with procedures for studying the behavior
of synaptic organelles during synaptic transmission. The authors
suggest that accurate information concerning the 3-dimensional
structural organization of the active zone material and the
molecular nature of its components is essential for a complete
understanding of the presynaptic mechanisms that are involved in
the regulation of synaptic transmission throughout the nervous
system.
-----------
M.L. Harlow et al: The architecture of active zone material at
the frog's neuromuscular junction.
(Nature 25 Jan 01 409:479)
QY: Uel J. McMahan: ujmcmahan@stanford.edu
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 16Mar01
For more information: http://scienceweek.com/swfr.htm

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5. PALEONTOLOGY: ON THE SKULL OF THE MIGHTY ALLOSAUR
     The term "Theropoda" (theropods) refers to a suborder of
dinosaurs, all of which were carnivorous, that ranged in size
from that of a chicken to the huge Tyrannosaurus, which weighed 6
tons or more. Theropod fossils have been recovered from the late
Triassic through the late Cretaceous periods (from 230 to 66.4
million years ago), and from all continents except Antarctica.
All the theropods were bipeds, with strong hind legs designed for
support and locomotion, and with short forelimbs and mobile hands
apparently adapted for grasping and tearing prey. Theropod feet
usually resembled the feet of birds, and many researchers believe
that all modern birds are descended from one lineage of small
theropods.
     The allosaurs are a genus of large theropod fossils from
late Jurassic to early Cretaceous, and these dinosaurs were
apparently the top Jurassic predator. Allosaur fossils have been
found in North America, Africa, and Australia. These animals,
standing approximately 4 meters high, weighed 2 tons and grew to
10.5 meters in length, and perhaps to 12 meters in length. Half
the length consisted of a well-developed tail that probably
functioned as a counterbalance for the body. The skull was
extremely large relative to the compact body and contained
several large openings that reduced its weight. The powerful jaws
had large pointed teeth, the flexible jaws allowing the animal to
take large bites of its prey. It is believed that allosaurs
preyed upon medium-sized dinosaurs, possibly hunting in groups,
but it may also have been a scavenger that fed on carcasses of
dead or dying animals.
     In general, "finite element analysis" is a numerical
technique in which a complex geometrical problem is broken up
into a system or more manageable problems, the break-up process
based on geometry and producing a system of equations that can be
solved by conventional methods. The method was outlined by the
mathematician Richard Courant (1888-1972) in 1943 and put into
practical use in the 1950s by aeronautical engineers. In the
modern most common version of the finite element method, the
domain to be analyzed is divided into cells ("elements"), and the
mechanical forces acting within each element are interpolated in
terms of displacements at a few points around the element
boundary called "nodes". With this technique, the mechanical
strain at every point can be expressed in terms of nodal
displacements, and considering the stresses associated with these
strains, and the given properties of the material, what is
generated is a system of simultaneous equations that can be
solved by numerical computer techniques. In the present context,
"computerized tomography" (computed tomography) of an allosaurus
skull was used to provide detailed quantitative input data for
finite element analysis. In general, in computerized tomography,
a narrow beam of x-rays sweeps across an area or object and is
recorded by a radiation detector as a pattern of electrical
impulses. Data from many such sweeps are integrated by a computer
to assess the density at thousands of points.
... ... E.J. Rayfield et al (7 authors at 4 installations, UK US
CA) present an analysis of cranial design and function in an
allosaur, the authors making the following points:
     1) The authors point out that finite element analysis is
used by industrial designers and biomechanicists to estimate the
performance of engineered structures or human skeletal and soft
tissues subjected to varying regimes of stress and strain. The
method is only rarely applied to problems of biomechanical design
in animals, despite its potential for use in structure-function
analysis. Non-invasive techniques such as computed tomography
scans can be used to generate accurate 3-dimensional images of
structures such as skulls, and these images can then form the
basis of an accurate finite element model.
     2) The authors report they have applied computed tomography
and finite element analysis to the long skull of the carnivorous
theropod dinosaur Allosaurus fragilis. The authors report they
have generated the most geometrically complete and complex finite
element analysis model of the skull of any extinct or extant
organism. They have used the model to test the mechanical
properties of the skull, and to examine in a quantitative manner
long-held hypotheses concerning overall shape and function.
     3) The authors suggest the combination of a weak muscle-
driven bite force, a relatively light and open skull and
architecture, and an unusually high cranial strength, indicates a
very specific feeding behavior for this animal. The authors
suggest their results provide quantitative evidence to indicate
that during attack or feeding, Allosaurus generally used a high
velocity impact of the skull into its prey: "An analog would be a
person wielding a large and heavy hatchet. Aided by sharp,
recurved teeth and powerful neck musculature driving the skull
downwards and then imparting a retractile force, portions of
flesh were sliced, torn away and swallowed." The crushing bite of
Tyrannosaurus rex apparently represents a specialization towards
carcass dismemberment, and possible the tackling of larger and
heavily armored prey. In contrast, Allosaurus may have "traded" a
heavy skull and bite strength for greater speed and mobility of
upper jaw impact in order to capture lighter and more agile
animals.
     4) Concerning the technique of the study, an almost complete
skull of Allosaurus fragilis from the Museum of the Rockies
(Montana State University, US) was subjected to computed
tomography to obtain a series of transaxial scan images separated
by 4-millimeter intervals, and (x,y) coordinates from the
computed tomography images were imported into a commercial finite
element modeling and analysis software package COSMOS/M 2.0
(Structural Research and Analysis Corporation, US).
     5) In summary, the authors suggest their results demonstrate
the inherent potential of finite element analysis for testing
mechanical behavior in fossils in ways that until now have been
impossible.
-----------
E.J. Rayfield et al: Cranial design and function in a large
theropod dinosaur.
(Nature 22 Feb 01 409:1033)
QY: Emily J. Rayfield: eray@esc.cam.ac.uk
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 16Mar01
For more information: http://scienceweek.com/swfr.htm

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6. ORIGIN OF LIFE: THE HABITAT AND NATURE OF EARLY LIFE
Central to many scientific and philosophical problems, and to any
consideration of extraterrestrial life, is the question of the
origin of life on Earth. Of particular significance is our
understanding of the early history of Earth and of the time
during which life apparently first appeared on the planet.
... ... E.G. Nisbet and N.H. Sleep (2 installations, UK US)
present a review of current research on the habitat and nature of
early life on Earth, the authors making the following points:
     1) The current consensus view is that the Solar System began
after one or more local *supernova explosions approximately 4.6
billion years ago. In one generally accepted scenario of the
later stages of accretion of the Solar System, it is proposed
that there were approximately 500 *planetesimals, bodies
approximately the size of the Moon, in the region now occupied by
Mercury, Venus, Earth, and Mars (the "inner planets"). Venus,
Earth, and Mars all received during their formation water vapor
and carbon, perhaps with early oceans on all three. But other
models are also possible. The fate of the volatiles associated
with each planet was completely different: a) Venus is dry, with
a surface now at approximately 500 degrees centigrade under 90
*bar of carbon dioxide. b) Mars is in *permafrost. c) Earth has
approximately the same external inventory of carbon dioxide as
Venus, and both planets radiate heat to space at very similar
"effective" temperatures, but for Earth most of the carbon
dioxide is in the form of carbonate minerals (e.g., limestone).
The carbon dioxide blanket on Earth is less dense, and so the
oceans can exist. 
     2) Water is a strong *greenhouse gas, and at some stages
early in the history of Venus and Earth water vapor was probably
present high in the atmosphere. Such water vapor would have been
*photolyzed into hydrogen and oxygen, and the hydrogen present in
the upper atmosphere would have been lost rapidly to space.
Deuterium would have been lost also, but being more massive,
would have been lost more slowly. In comparison to the deuterium
content that is thought to have been originally in the planetary
mix, the atmosphere of Venus has a strong deuterium enrichment,
and the simplest explanation is that Venus lost its water early
in its history when a runaway greenhouse developed. In this
model, Venus initially had oceans and a warm surface of
approximately 75 degrees centigrade. Water was partitioned into
the high atmosphere, there photolyzed, hydrogen was lost and the
planet dehydrated and left more oxidized. Alternately, if Venus
has or had a molten *magma ocean in its *mantle, it may there too
have sequestered deuterium-poor hydrogen ("light hydrogen") as
OH. Mantle minerals are typically light, or depleted in deuterium
relative to sea water.
     3) The authors summarize their view of the early history of
Earth: Our planet is more than 4.5 billion years old. Massive
bombardment of the planet occurred in the first 500 to 700
million years, and the largest impacts would have been capable of
sterilizing the planet. Probably until 4 billion years ago or
later, occasional impacts might have heated the ocean over 100
degrees centigrade. Life on Earth dates from before approximately
3.8 billion years ago, and is likely to have experienced one or
more hot-ocean bottlenecks. Only organisms optimally living in
water at 80 to 110 degrees centigrade (hyperthermophile
organisms) would have survived. It is possible that early life
diversified near *hydrothermal vents, but hypotheses that life
first occupied other pre-bottleneck habitats are tenable
(including transfer from Mars on ejecta from impacts there).
Early hyperthermophile life, probably near hydrothermal systems,
may have been *non-photosynthetic, and many *housekeeping
proteins and biochemical processes may have an original
hydrothermal heritage. The development of anoxygenic and then
oxygenic photosynthesis would have allowed life to escape the
hydrothermal setting. By approximately 3.5 million years ago,
most of the principal biochemical pathways that sustain the
modern biosphere had evolved, and were global in scope.
-----------
E.G. Nisbet and N.H. Sleep: The habitat and nature of early life.
(Nature 22 Feb 01 409:1083)
QY: E.G. Nisbet: Department of Geology, University of London, UK.
-----------
Text Notes:
... ... *supernova: A violent explosion in which certain stars
end their lives. The star may become more than 10^(9) times as
bright as the Sun and may outshine its host galaxy for weeks.
... ... *planetesimals: Planetesimals are bodies with dimensions
of 10^(-3) to 10^(3) meters that are believed to form planets by
a process of accretion. The term "accretion" refers to an
aggregation, an increase in the mass of a body by the addition of
smaller bodies that collide and adhere to it, provided the
relative velocities are low enough for coalescence.
... ... *bar: 1 bar equals 0.99 atmosphere.
... ... *permafrost: In general, permanently frozen ground.
... ... *greenhouse gas: The physical basis of the so-called
"*greenhouse effect" is essentially simple: carbon dioxide gas is
transparent to visible light but relatively opaque to infrared
radiation. The same is true of glass. Relatively high-energy
visible light radiation from the sun passes inward through the
atmosphere, warms the surface of the Earth, which then radiates
lower energy in the form of infrared radiation (heat) back to the
atmosphere. But if the atmosphere has a concentration of infrared
impenetrable gases such as carbon dioxide, the infrared radiation
cannot pass out, and the surface of the Earth underlying the
atmosphere cannot cool, and the surface of the Earth thus will
continue to grow hotter.
... ... *photolyzed: In general, any chemical reaction produced
by exposure to light or ultraviolet radiation.
... ... *magma: In general, any molten mass of rock.
... ... *mantle: Seismic studies indicate the interior of the
Earth consists of three parts: a metallic core, a dense rocky
mantle, and a thin low-density crust. In this context, the
assumption is that Venus, like Earth, has a mantle layer between
its core and its crust.
... ... *hydrothermal vents: In this context, the term
"hydrothermal" refers to hot solutions rising from cooling molten
rock (magma). "Hydrothermal vents" are hot springs occurring in
volcanic regions of the ocean floor.
... ... *non-photosynthetic: In general, photosynthesis is the
utilization of light energy to power biosynthesis.
... ... *housekeeping proteins: So-called "housekeeping" proteins
are proteins involved in essential functions such as metabolic
cycles.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Mar01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ORIGIN OF LIFE:
ATMOSPHERIC AEROSOLS AS PREBIOTIC CHEMICAL REACTORS
     An amphiphile is a molecule that has a polar head attached
to a long hydrocarbon tail. The result is that one part of the
molecule (the polar head) interacts strongly with water, while
the other part of the molecule (the long hydrocarbon tail)
interacts strongly with nonaqueous phases or with the hydrocarbon
tails of neighboring same-species molecules via dispersion forces
(van der Waals forces). Amphiphile molecular systems are usually
self-organizing, the spontaneous organization maximizing all
possible interaction energies, and a "micelle" is a spontaneously
forming colloidal aggregate of amphiphiles, usually in a
spherical arrangement. Such self-organization of amphiphiles may
also occur in a gas phase, with particular parts of molecules
arranged to be in the interior of the micelle, while other parts
are external and exposed to the gas. In general, in any system,
both the existence and detailed structure of micelles depend on
the specific chemical species in the system, the paramount factor
the tendency of molecular aggregates to arrange themselves in a
way that maximizes interaction energies.
     In the first half of the 20th century, when various micellar
systems were first investigated (albeit their detailed molecular
structure was not yet clearly established), both micelles and
larger colloidal aggregates were considered possible protobiotic
structures, primarily for two reasons: 1) the sizes of these
structures are of the same dimensions as biological cells; 2) and
more important, the membranes of all biological cells (i.e., the
barriers that separate the internal cellular contents from the
external environment) are composed mainly of amphiphiles, and
indeed such amphiphiles are evidently absolutely necessary for
biological membranes to exist.
     In general, the term "aerosol" refers to a dispersion in
which a finely divided solid is suspended in air and the
particles are of colloidal dimensions. The term "colloidal
dimensions" refers to the range approximately 1 nanometer to 100
nanometers in diameter.
... ... C.M Dobson et al (5 authors at 3 installations, UK US)
now present a proposal that large populations of aerosols in
micelle form could have been of great importance in the origin of
life on Earth. The authors make the following points:
     1) The authors point out that aerosol particles in the
atmosphere have long been known to scatter sunlight and thus to
have a substantial influence on the temperature of the Earth.
Recent real-time observations of the chemical composition of
individual aerosol particles have shown an unexpected and
remarkably high content of organic molecules, and these
observations can be accounted for by a model involving an
inverted micellar structure in which surfactants form a spherical
monolayer enclosing an aqueous interior. The authors propose that
analogies in size, form, and composition between these aerosols
and single-celled organisms such as bacteria suggest that similar
atmospheric particles could have been the precursors of living
systems on Earth.
     2) The authors suggest that large populations of aerosol
particles would have provided an environment for the
concentration of prebiotic molecular species and for their
chemical transformation through exposure to the fluctuating
fields of humidity, temperature, and sunlight available in the
atmosphere at different altitudes and latitudes. Coagulation and
division of the particles could have resulted in an increased
diversity of molecular species and an early mechanism for
reproduction and replication of successful molecular populations.
     3) The authors point out that it has long been known that
aerosols are formed by wind-driven wave action followed by
bubble-bursting at the ocean surface. Aerosols, therefore, act as
separators that concentrate surfactants, such as long-chain
carboxylic acids, at the air-water interface. There is evidence
that organic molecules partition in laboratory-formed aerosols
such that the more hydrophobic molecules in a mixture tend to
migrate to the outside of the droplets. The authors suggest it is
important to note that aerosol droplets (radii 10^(-7) to 10^(-6)
meters) are different in crucial respects from cloud droplets
(radii 10^(-5) to 10^(-4) meters) and raindrops (radii
approximately 10^(-3) meters). The fractional organic content of
these larger "hydrometeors" is small, is minuscule for
surfactants, and is therefore a significant handicap for their
previously proposed role in the origin of life.
     4) In summary, the authors suggest that atmospheric aerosols
coated with organic surfactant films appear to offer a number of
attractive features as versatile chemical reactors in the
prebiotic production of polymeric molecular species. These
features include their mobility through a wide range of
temperature and radiation fields, their frequent, widespread, and
continual formation, their natural ability to concentrate aqueous
solutions, and their ability to coagulate and divide, thus
sharing contents and information. Atmospheric dispersion by fluid
motion allied to diffusion would ensure that not all aerosols
would share any evolved advantage, so natural selection would not
be inhibited. The natural tendency of aerosols, through the
forces of gravity, aerodynamics, drag, and surface tension is to
be of the same size as terrestrial single-cell organisms. The
authors suggest their model addresses several key issues in the
development of prebiotic chemistry and its conversion to
biochemistry. At least the first steps of the evolution of
monomers in aerosols are testable by experiment, particularly
under light of shorter wavelengths than those cut off by ozone in
the present atmosphere.
-----------
C.M. Dobson: Atmospheric aerosols as prebiotic chemical reactors.
(Proc. Natl. Acad. Sci. US 24 Oct 00 97:11864)
QY: Adrian F. Tuck: tuck@al.noaa.gov
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 10Nov00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ORIGIN OF LIFE: PRODUCTION OF PEPTIDES ON INORGANIC SURFACES
The primordial process responsible for the activation of amino
acids and the formation of peptides under primordial conditions
is one of the great riddles of the origin of life. ... ... Huber
and Wachterschauser (Technische Universitat Munchen, DE) now
report that in experiments modeling volcanic or hydrothermal
settings, amino acids were converted into their peptides by use
of coprecipitated (Ni,Fe)S and CO in conjunction with H(sub2)S
(or CH(sub3)SH) as a catalyst and condensation agent at 100
degrees centigrade and pH 7 to 10 under anaerobic aqueous
conditions. The amino acids involved in the experiments were
phenylalanine, tyrosine, and glycine. The authors suggest their
results demonstrate that amino acids can be activated under
geochemically relevant conditions, and that the results support a
thermophilic origin of life with a primordial surface metabolism
on transition metal sulfide minerals. They further suggest that a
continuously recycling library of peptides was generated on the
surfaces of a library of (Fe,Ni)S structures, and that the
results raise the possibility that CO and Ni had a much greater
role in the primordial metabolism than in any of the known extant
metabolisms. They point out that all known extant organisms are
found in habitats with low activities of CO and Ni, and they
suggest this could explain why organisms resorted to the
formation of CO from CO(sub2) and to the elimination of nickel
from many enzymes.
QY: Gunter Wachterschauser, Tal 29, D-80331 Munchen, DE.
(Science 31 Jul 98 281:670) (Science-Week 28 Aug 98)
-------------------
Related Background:
PREBIOTIC ORGANIC COMPOUNDS: OCEANIC PROTECTION FROM SOLAR UV
It is generally believed that the Earth's primitive atmosphere
lacked oxygen, and therefore that an ozone layer protective
against ultraviolet radiation did not exist. This is considered
to be a serious problem for the accumulation of prebiotic organic
compounds on Earth and on Mars, and this problem would have been
worsened by the theoretically expected elevated ultraviolet
radiation production of the early Sun. Protection from
ultraviolet radiation is one of the motivations for proposing an
origin of life in submarine vents, benthic regions, and in deep
subsurface environments. Most attempts to deal with this problem
have involved atmospheric absorbers such as H(sub2)S, SO(sub2),
S(sub8), and organic hazes. ... ... Cleaves and Miller
(University of California San Diego, US) present an analysis of
the problem and report that even in the absence of atmospheric
shielding there would have been sufficient ultraviolet absorbers
in the ocean to allow for the accumulation of organic material.
These absorbers include organic polymers from electric discharges
and hydrogen cyanide polymerizations, solubilized elemental
sulfur, and inorganics such as Cl(-), Br(-), Mg(2+), SH(-),
Fe(2+). Complete ultraviolet protection could also be provided by
a frozen ocean, an oil slick, or large amounts of organic foams.
The authors suggest that oceanic ultraviolet protectors increase
the size of planetary habitable zones and thereby increase the
number of planets on which life may have arisen.
QY: Stanley L. Miller: smiller@ucsd.edu
(Proc. Natl. Acad. Sci. US 23 Jun 98 95:7260)
(Science-Week 17 Jul 98)
-------------------
Related Background:
BIOCHEMICAL EVOLUTION: POLYMERIZATION ON MINERAL SURFACES
J. Smith (University of Chicago, US) proposes a conceptual
framework for consideration of the origins of replicating
biopolymers. Although extended Darwinian natural selection
coupled with Mendel-Watson-Crick genetic inheritance/mutation
provides a plausible framework for integrating the patchy
paleontological record with the increasingly complex biochemical
zoo of the present Earth, the actual chemical beginning of "life"
still poses major challenges. How could the first replicating and
energy-supplying molecules have been assembled from simpler
materials that were undoubtedly available on the early proto-
continents? Catalysis at mineral surfaces might generate
replicating biopolymers from simple chemicals supplied by
meteorites, volcanic gases, and photochemical gas reactions. But
many ideas are implausible in detail because the proposed mineral
surfaces strongly prefer water and other ionic species to organic
ones. The molecular sieve silicalite (Union Carbide; = Al-free
Mobil ZSM-5 zeolite) has a 3-dimensional 10-ring channel system
whose electrically neutral silicon-oxide surface strongly adsorbs
organic species over water, and the ZSM-5 type zeolite mutinaite
has recently been found in Antarctica. The author proposes that
zeolites with similar structures may have existed on the surface
of Earth during its life-origin phase, and that polymer migration
along weathered silicic surfaces of micrometer-wide channels of
feldspars might have led to assembly of replicating catalytic
biomolecules and perhaps primitive cellular organisms. The author
suggests that weakly metamorphosed Archaean rocks might retain
microscopic clues to the proposed mineral adsorbent/catalysts,
and that other frameworks are also possible, including ones with
laevo/dextro one-dimensional channels.
QY: Joseph V. Smith: smith@geol.uchicago.edu
(Proc. Natl. Acad. Sci. US 31 Mar 98 95:3370)
(Science-Week 8 May 98)
-------------------
Related Background:
ORIGIN OF LIFE: THE PRESENT STATUS OF CHEMICAL THEORY
The essential question involved in the origin of what we call
life is how can order arise from disorder? At the present time,
this question is approached on two fronts: 1) study of the
principal features of self-organizing systems, systems in which
order does arise from disorder, systems in which order is indeed
demanded from disorder on thermodynamic grounds; and 2) study of
the detailed chemistry of such systems, the chemistry of
organization and the chemistry of components. In the case of
components, it is essential that appropriate self-organizing
components exist in the first place if they are to become self-
organized, and such candidate components are thus the focus of
much chemical research in this area. In 1953, the chemist Stanley
Miller reported what soon became a famous experiment. To water
under a gas mixture of methane, ammonia, and hydrogen, he added
an electrical discharge. After one week of continuous electrical
discharge, he found that a number of important biological
molecules, including amino acids, had been formed. Miller
proposed his experiment as a model for the conditions under which
the essential compounds necessary for life originated . The
Miller experiment was a watershed, and it began a new era of
experimentation and analysis of possible primordial components.
Coupled with this, were the new important discoveries by
astrophysicists of the presence of organic molecules in the
interstellar medium and in meteorites. In a review of origin of
life theories, P. Radetsky (Univ. of California Santa Cruz, US)
points out that the Miller theory is no longer the consensus
theory, that contemporary geologists believe the primordial
atmosphere consisted primarily of carbon dioxide and nitrogen,
which are less reactive than the gases in the Miller experiment,
and that the field is currently embroiled in controversy fueled
for the most part by an absence of hard fact.
QY: Peter Radetsky, Univ. of California Santa Cruz 408-429-4008
(Earth February 1988) (Science-Week 2 Jan 98)
For more information: http://scienceweek.com/swfr.htm

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7. IN FOCUS: ON ELEMENTARY PARTICLES IN PHYSICS
[Editor's note: The following passage, written more than 40 years
ago, was published shortly before the introduction of the idea of
"quarks" by Murray Gell-Mann revolutionized particle physics. The
words are still relevant: the term "elementary particle" is
unstable.]
-----------
"In popular usage, the term "elementary particle" signifies an
ultimate constituent out of which all matter is compounded. In
physics, the usefulness of the concept depends very much on our
state of knowledge, the hierarchy of forces with which one is
dealing, and the order which is introduced into the description
of the empirical facts. From one point of view, any particle with
a well-defined mass, charge, and intrinsic angular momentum (or
spin) is an elementary particle and, in this context, even a
molecule could be regarded as elementary. However, when the
electromagnetic law of force was established between the atoms in
a molecule and also between the electrons and the positively
charged nucleus of the atom, it was much more convenient at that
stage to think of the electron and the various types of atomic
nuclei as the elementary particles. When quantum mechanics was
developed and the wave-particle dualism became an essential
ingredient of our understanding of all atomic phenomena, it was
proper to add the photon to the list of elementary particles.
When the neutron was discovered and the existence of a distinct
nuclear force was established, it became more advantageous to
think of the neutron and proton as the elementary particles out
of which atomic nuclei are built up. Within this context, for
example, the completely stable deuteron, with a well-defined
mass, charge, and spin, is considered a composite structure,
whereas the unstable neutron is treated as an elementary
particle. The reason for this anachronistic point of view is that
within the hierarchy of strong (or nuclear), electromagnetic, and
weak forces, the neutron lives for a very long time [10^(3)]
seconds on the nuclear time scale of 10^(-23) second."
-----------
R.E. Marshak: "Elementary Particles of Modern Physics"
(Science 29 Jul 1960 132:269)
-------------------
SCIENCE-WEEK http://scienceweek.com 16Mar01

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8. FROM THE SCIENCEWEEK ARCHIVE:
ON AMMONIA AND THE POPULATION EXPLOSION
Ammonia [NH(sub3)], a nitrogen hydride, is a colorless gas with a
rather interesting human history that ranges from its discovery
by the remarkable chemist Joseph Priestley (1733-1804) to the
first large-scale synthetic production and use of ammonia in
synthetic fertilizers and explosives in the 20th century. The
human requirement for synthetic fertilizers and explosives is an
instance of irony in the application of science, since the major
use of synthetic fertilizers is in the production of crops to
feed people, and the major use of explosives is in the production
of weapons to kill people. Nitrogen compounds are essential to
fertilizers and explosives, but in the early 20th century the
best large-scale source of such compounds was in the nitrate
deposits of Chile [*Note #1], which at that time was quite remote
from Europe. Another possible source of nitrogen compounds, only
theoretical at the time, was Earth's atmosphere, since the
atmosphere is mostly nitrogen gas and therefore constitutes an
inexhaustible supply. If atmospheric nitrogen could be converted
to ammonia, the ammonia could be used in the synthesis of various
nitrogen compounds, including fertilizers and explosives. Fritz
Haber (1868-1934) and Carl Bosch (1874-1940) are credited with
the discovery of the Haber-Bosch process for the synthesis of
ammonia from its elements, a discovery that literally altered the
course of 20th century history. The basis of the process is the
combining of nitrogen and hydrogen at high pressure over a
catalyst. Haber, who first demonstrated the synthesis in 1909,
received the Nobel Prize for Chemistry in 1918; Bosch, who
engineered the application of the method to the large-scale
production of ammonia, received the Nobel Prize for Chemistry in
1931 [*Note #2]. ... ... Vaclav Smil (University of Manitoba, CA)
presents an historical essay on the Haber-Bosch discovery, the
author making the following points:
     1) The author poses the question: What is the most important
invention of the 20th century? The usual answers include
airplanes, nuclear energy, space flight, television, and
computers, but none of these are critical to human well-being.
The synthesis of ammonia from its elements, however, is critical:
the world's population could not have grown from 1.6 billion in
1900 to the 6 billion of today without the Haber-Bosch process.
     2) The synthesis of ammonia belongs to that special group of
discoveries -- including Edison's light bulb and the Wright
brothers' flight -- for which we can pinpoint the date of the
decisive breakthrough. The archives of Badische Anilin-Und Soda-
Fabrik (BASF) contain a letter from Haber, at that time Professor
of Physical Chemistry at Technische Hochschule in Karlsruhe, to
the company directors, a letter in which Haber recounts how the
previous day the first demonstration to company scientists of the
synthesis of ammonia from nitrogen and hydrogen was made: "All
parts of the apparatus were tight and functioned well, so it was
easy to conclude that the experiment could be repeated."
     3) Although a number of company officials lacked confidence
in the application of Haber's method because of the high pressure
(over 100 atmospheres) required, Carl Bosch, who managed the BASF
nitrogen-fixation research, was apparently confident: "I believe
it can go. I know exactly the capability of the steel industry.
It should be risked." It was Bosch who was responsible for the
development of the proper steel housing necessary for large-scale
ammonia production.
     4) The present world output of ammonia amounts to
approximately 130 million metric tons per year, and 80 percent of
this goes into fertilizers, of which urea is the most important.
The ammonia is absolutely essential to sustain today's
population: rich countries might fertilize much less by cutting
excessive food production and by eating fewer animals, but even
the most assiduous recycling of organic wastes and the widest
planting of *nitrogen-fixating legumes could not supply enough
nitrogen for land-scarce, poor and populous nations. For several
decades now, virtually all the fixed nitrogen added to the fields
of China, Egypt, and Indonesia has come from synthetic
fertilizers.
     5) The author concludes: "Without this [the Haber-Bosch
process], almost two-fifths of the world's population would not
be here -- and our dependence will only increase as the global
count moves from 6 to 9 or 10 billion people."
-----------
Vaclav Smil: Detonator of the population explosion.
(Nature 29 Jul 99 400:415)
QY: Vaclav Smil: Dept. of Geography, University of Manitoba, CA
-----------
Text Notes:
... ... *Note #1: During World War I (1914-1918) access to the
Chilean nitrate deposits by Germany was almost impossible, with
imports of nitrates blocked by the British navy. The German
military needed explosives, which required nitrates, which
required a source of usable nitrogen. This was the main impetus
for the development of the large-scale production of ammonia by
Bosch and BASF. Many historians believe that if Germany had had
to depend only on Chilean nitrates for explosives, World War I
would have ended in 1916, with several million lives saved.
... ... *Note #2: The personal story of Fritz Haber is
interesting. Haber became a prominent chemist following his
discovery of the synthesis of ammonia from nitrogen and hydrogen.
He was extremely patriotic, and during the war he devoted great
efforts to the development of gas warfare, directing the first
warfare use of chlorine gas in 1915, and of mustard gas in 1917.
In the history of war, the beginning of gas warfare is dated as
April 22, 1915, "the day at Ypres when Haber's gas blowing
process surprised and overpowered the enemy lines for the first
time." Because of his work in gas warfare, there were many
protests when Haber was awarded the Nobel Prize after the war
ended. Following the war, and the huge reparations demanded from
Germany by the Allies, Haber worked to isolate gold from seawater
in order to pay the reparations. The yield was too small and
research failed. In 1933, when the Nazis came to power in
Germany, Haber's patriotic services in ammonia synthesis for
explosives, gas warfare, and the attempted isolation of gold from
seawater were dismissed as irrelevant because Haber was a Jew,
and Haber was forced to give up his post and flee Germany. He
went first to England, then decided to go to Palestine, but he
died in Switzerland on his way south. Carl Bosch had a different
fate: Bosch, who was not a Jew, remained in Germany as a
prominent scientist. In 1933, Bosch actually cautioned Hitler
against the policy of dismissing non-Aryan scientists, pointing
out to Hitler the severe damage which this policy threatened to
inflict on the pursuit of chemistry and physics in Germany.
Hitler's response: "Then we'll just get along without physics and
chemistry for a hundred years!" In 1935, as the Nazi era
continued, Bosch succeeded Max Planck as head of the Kaiser
Wilhelm Society (now called the Max Planck Society).
... ... *nitrogen-fixating legumes: In leguminous plants such as
beans and peas, the symbiotic bacteria Rhizobium form
characteristic root nodules, the bacteria supplying the plant
with usable nitrate obtained from atmospheric nitrogen, while the
bacteria obtain carbohydrates from the plant. In general, the
term "nitrogen-fixation" refers to any fixation of nitrogenous
compounds from atmospheric nitrogen. In nature, this is achieved
by the normal metabolism of specialized soil bacteria (e.g.,
Rhizobium), and also by the electric discharges of lightening in
the atmosphere. The Haber-Bosch process is industrial nitrogen-
fixation.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 20Aug99
For more information: http://scienceweek.com/swfr.htm

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