- The Big, Big Chill
Note: The following news item is drawn in part from an
article in Scientific American (January 2000) by Paul
F. Hoffman and Daniel P. Schrag of Harvard University.
- One of the major ecological concerns today is greenhouse warming of
the climate. In the January issue of Scientific American, Paul F.
Hoffman, a Harvard University geologist, and Daniel P. Schrag, a Harvard
oceanographer, treat us to a picture of ancient climate variations far in
excess of any predictions for the current warming. The snowball earth
hypothesis, first proposed to explain geological observations from the 1960s,
puts the earth under a planetary ice sheet averaging a kilometer deep and
extending to the poles. Initial objections to this hypothesis, e.g. that it
would have left no life alive to formulate the hypothesis, have fallen to
other discoveries, e.g. life near deep-ocean vents that lives off of chemical
and thermal energy from the earth's interior.
- Hoffman and Schrag paint a more complex picture than the initial
"frozen solid for millions of years" scenario. The snowball earth had
occasional meltdowns, driven by a carbon dioxide cycle. In the era of the
snowball earth, there were many small continents near the equator. This made
it easier for rains to fall on land, dissolving and sequestering carbon
dioxide. Since carbon dioxide traps heat, the earth cooled, permitting polar
caps to expand. Polar caps have a very high albedo, and so more light is
reflected back into space. This lowers the temperature more, expanding the
ice caps more, until finally the ice caps meet at the equator. A snowball
earth event has begun.
- One of the mysteries that led to a more complex picture than the
initial scenario just described is widespread deposits of carbonate rock,
from the snowball era, that form in warm water. During the entire period in
question, volcanoes belched a certain amount of carbon dioxide each year.
When the rain is scrubbing carbon dioxide to initiate a snowball event, this
scarcely matters. After the ice closes in, however, this carbon dioxide
begins to accumulate. After 10 million years this carbon dioxide has
restored the greenhouse effect to the point where it overcomes even the high
albedo of the planetary ice sheet. The ice begins to melt. This exposes
open water, which absorbs sunlight far more efficiently than ice. The
melting thus feeds on itself and a very warm period follows. The carbon
dioxide built up during the ice event exceeds that present at the beginning
of the snowball event, and the earth warms to an average temperature of as
much as 50 degrees centigrade. While these super-warm episodes are short,
they do permit the formation of the formerly mysterious carbonate rock.
- The ice phase of a snowball earth event is long and provides ample
time for deep ocean vent communities to diverge along different evolutionary
paths. The resource-rich heat shocks following the melting would permit some
radiation and diversification. The end of the most recent snowball earth
event correlates well with the Cambrian explosion and may have been the
trigger. One question that remains is the reason the cycle of snowball
events ended. Maybe the continents are no longer in the right configuration,
or maybe the emergence of multicellular life disrupted the cycle. In any
case, the geological evidence underlying the snowball earth hypothesis shows
the earth to be capable of far more extreme climate variation than was
previously suspected.
- A Chip for All Seasons
Note: The following news item is drawn in part from an
article in The Economist (29 January 2000) prepared by
staff writers.
- The past is the bane of microchip designers. Your blazing Pentium
III with the new multimedia hardware has the ability to run software written
for the 8086-based IBM PC. This need not slow the chip down too much;
special hardware detects old code and transforms it into something that runs
well on the new chip. The price is paid in the power to run the transistors
that make up these translation circuits. What is to be done then? Will the
chips designed in 2015 pay the energetic cost of the 8086 and, for that
matter, the clunky obsolete multimedia of the Pentium III?
- An article in a recent issue of The Economist suggests the
answer is "no". Transmeta of Santa Clara, California, has developed a chip
that not only has a very efficient instruction set of its own, but also uses
software to perform many of the compatibility tasks done in silicon in other
chips. The most obvious benefit is that the Transmeta chip can emulate a
Pentium III, at full speed, with about a quarter of the power. Many of the
things that make a P-III so cool --- e.g., instruction segmentation and
anticipation of future instructions --- happen in a layer of software on the
Transmeta chip. This means the Transmeta chip can be upgraded quite a bit
before it needs to be replaced and can emulate many different types of
processors. Also, unlike chips that use hardware to break old instructions
into more efficient pieces, the Transmeta chip can save the result of such
translation. In contrast, each time a P-III executes an archaic instruction
it re-translates it again, burning power to do so.
- Another benefit of placing some of the chip's low-level
functionality into a software layer comes from the chip's ability to optimize
its own performance. The simplest instance of this behavior is the
Transmeta's ability to imitate a slower chip when the user is doing something
such as word-processing. Slower chips use less power, so a Transmeta chip
will help your laptop's batteries to last longer. More complex types of
self-modification are implemented by having the chip statistically track
instruction usage and apply an increasing amount of time optimizing code that
is used more often. From the user's point of view, the chip "gets used to" a
program as it goes along, increasing execution speed as it optimizes itself
to run the program's code. The Transmeta chip may end the problem of
vestigial code restricting processor performance, to the substantial benefit
of power users everywhere.
- The Chimp's Magic Number is Five
Note: The following news item is drawn in part from an
article in Nature (6 January 2000) by Nobuyuki Kawai and
Tetsuro Matsuzawa.
- It is part of the folklore of cognitive science that people find it
much easier to remember seven or fewer things than eight or more. Writing in
a recent issue of Nature, Nobuyuki Kawai and Tetsuro Matsuzawa
(Primate Research Institute, Koyoto University) report that their chimpanzee
test subject has a similar cognitive limit that cuts in at five objects.
Given that chimps are the closest living relative of humans, this is an
intriguing elucidation of our similarity and difference.
- To measure the magic number for chimps, Kawai and Matsuzawa started
with a chimp named Ai that could already order in ascending order a set
of numbers listed on a computer screen. They modified the test by
masking the numbers after Ai indicated which one came first. To finish
ordering the numbers, Ai had to memorize all of the numbers in the list. Ai
achieved a 90% accuracy rate for sets of four numbers and a 65% accuracy rate
for sets of five numbers. This level, while well below perfection, is well
above chance.
- Another "Ocean" on a Jovian Satellite
Note: The following news item is drawn in part from an
article in Science (3 December 1999) by staff writer Richard A. Kerr.
- A perennial topic in Complexity-at-Large (Jan.-Feb. 1999,
Nov.-Dec. 1999, Jan.-Feb. 2000) has been extra-terrestrial oceans. From
Europa's subsurface sea to theoretical bodies kept liquid by radio-decay on
sunless planets, we have thus far concentrated on bodies of water. In a
recent issue of Science, Richard A. Kerr reports the possibility of
another sort of ocean. Io, the only one of Jupiter's moons not tagged with
evidence of a subsurface water ocean, may contain an ocean of molten sulphur.
Io's volcanism is extreme enough to be visible from orbit. Driving this
volcanism is a sub-surface reservoir of hot molten material composed mostly
of sulphur. The heat to keep this reservoir molten is maintained by tidal
stresses generated by Jupiter and the other Jovian moons. While this
subsurface ocean, at 2000 degrees Kelvin, is unlikely to harbor life, it does
provide an interesting contrast between Io and the other moons of Jupiter.
- Gravity Lost in Space
Note: The following news item is drawn in part from an
article in Science (7 January 2000) by Gary Gibbons.
- In a recent issue of Science, Gary Gibbons (Laboratoire de
Physique Theorique de l'Ecole Normale Superieure, Paris) reviews recent
developments in string theory. These new developments increase the
explanatory power of string theory while making it even more wierd.
- Before the new developments, string theory painted a picture of a
universe having ten dimensions: namely, the familiar four dimensions of space
and time, plus six compact dimensions. The compact dimensions are tiny, with
the distance across the universe in these extra dimensions being smaller than
the distance across an electron. The properties of a particle are dictated
by the way it folds in these six dimensions, as determined by a topological
oddity called a Calabi-Yau manifold.
- One thing the old string theory did not do was explain why
gravitation was so much weaker than the other fundamental forces. The new
developments revive an old and beautiful theory, formulated by Kaluza and
Klein, and fuse it with string theory. The result is an eleven-dimension
universe with a universal diameter somewhere between a centimeter and
infinite size. The new theory addresses the weakness of gravity in a curious
way. Particles carrying forces other than gravity are open strings, with
ends, and these ends anchor the particles in what we perceive as the normal
universe. Gravity is carried by strings that form closed loops. These loops
are not anchored and so may wander off into the additional dimension. The
gravity we feel is the projection of the gravitational force spreading
through the expanded space onto our perceived universe. This new proposal,
while increasing the mathematical beauty and explanatory power of string
theory, still awaits experimental test.
- Ultraviolet Sex Ratios in Blue Tits
Note: The following news item is drawn in part from an
article in Nature (23 December 1999) by Ben C. Sheldon, Staffan
Andersson, Simon C. Griffith, Jonas Ornborg, and Joanna Sendecka.
- An interesting thing about birds is that they see a fourth color, in
the ultraviolet, that we do not. This creates some interesting options for
birds that wish to appear colorful to prospective mates and drab to mammalian
predators. Natural selection can, in effect, export mating displays into the
ultraviolet where they attract attention from the smallest possible set of
opponents. Birds, such as the peacock, have also been at the core of debate
over sexual selection. With peacocks the classical question is whether
female preferences for longer tails drove the males tail beyond reasonable
size via a sort of sexual positive feedback loop. It is a vexed question as
to weather a beautiful tail demonstrates toughness ("I can survive while
carrying this thing, baby!") or is an honest advertisement of something like
a low parasite load.
- Entering the sexual selection fray with new data from the
ultraviolet, Ben C. Sheldon, Simon C. Griffith, and Joanna Sendecka of the
Animal Ecology and Evolutionary Biology Departments at Uppsala University in
Sweden, together with Staffan Andersson and Jonas Ornborg of the University of
Goteborg's Zoology Department, also in Sweden, show the situation has
unsuspected complexities. First of all, female blue tits lay more male eggs
if their mate has a higher ultraviolet reflectance. Implicit in this is the
ability of the mother to affect the sex of her offspring in some manner.
This continues the trend of recent years in discovering that random
genetically-determined sex is not the dominant system; turtles and alligators
pick their sex by the incubation temperature of their eggs while some fish
are male when small and female when large enough to carry eggs. The
researchers measured this modification of sex ratio in blue tits by masking
the ultraviolet reflectance of some male birds and checking the effect on the
sex ratio of their offspring.
- Sexual selection enters into these observations when one considers
the mother bird's strategy options. If you mate with a genetically superior
male, then having more male offspring enhances your descendant's prospects.
If you mate with an inferior male, daughters are your best bet. But why
should high ultraviolet reflectance indicate superiority? While this
question goes unanswered, studies of survival in the wild indicate that male
blue tits with higher ultraviolet reflectance do have a better chance of
surviving. The ultraviolet advertisement is an honest statement of quality
of the sort that might become involved in sexual selection. The blue tits
are an example of how the tangled threads of a complex system interact,
joining intricate questions at the hip, and making life interesting for
researchers.
- Exoplanets: Seeing is Believing
Note: The following news item is drawn in part from a preprint
of an article to appear in Astrophysical Journal Letters (January
2000) by Gregory W. Henry, Geoffrey W. Marcy, R. Paul Butler, and Steven
S. Vogt.
- Extra solar planets have appeared by the dozen in recent years.
Depending on your definition of planet, from 28 to 42 are listed in the
online Extra Solar Planets Encyclopedia:
http://cfa-www.harvard.edu/planets/.
So far, these extrasolar planets are detected by the wobbles they induce
in their primary stars. In an article to appear in Astrophysical
Journal Letters in January 2000, Gregory W. Henry of Tennessee State
University's Center for Excellence in Information Systems, Geoffrey
W. Marcy of the Astronomy Department at Berkeley, H. Paul Butler of the
Washington, D.C. Department of Terrestrial Magnetism, and Steven S. Vogt
of the Lick Observatory report a different sort of detection: a
planetary transit.
- In a transit, the decrease in the primary star's output is measured
as the planet passes in front of the star along the line of sight to earth.
Such transits are a far less reliable means of detecting exoplanets because
they require a somewhat unlikely alignment. They are superior to measuring
stellar wobble, though, because they give a better measurement of planetary
mass. Imagine that we are looking at a solar system from above or below so
that the orbits of planets form ellipses from our point of view. Then the
star's wobbles in response to the planet's pull are back-and-forth and so
cause no Doppler shift in the star's spectrum. If the plane of planetary
orbit is edge on to earth, then we see the largest possible amount of Doppler
shift when planets cause their primary star to wobble. In short, the size of
planets detected by Doppler-shift wobble has a fudge factor computed from the
angle of the orbital plane as seen from earth. With a planetary transit we
know the orbital plane is edge on to earth and we get exact mass figures for
the planet.
- The planetary transit measured by Henry et al. indicates that the
mass of the planet they detected transiting the G0 dwarf star HD 209458 is
62% of Jupiter's. Like most of the exoplanets detected so far, this one is
absurdly close to its primary star by the standards of our own solar system.
With a year of only 3.5 days, this planet is quite warm and so has a diameter
that is 142% of Jupiter's --- solar heating has reduced the planets density
considerably by spreading its gaseous outer layers.
tesfatsi@iastate.edu 
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