JMDMT 639 Microfossils of Cyanobacteria in Carbonaceous Meteorites Descrição do Vídeo:
The James M. DuPont Meteorite Collection -liquid
water. The water will not last forever, of course.
Above the zone of liquid water, Anders: Origin of
Carbonaceous Chondrites 523 there will be a permafrost
zone,* and the ice from this zone will evaporate at a
rate determined by its vapor pressure (Watson et al.,
1961). The vapor pres- sure depends upon the
temperature, which in turn depends on the distance from
the sun. For a body with 100-km. radius, with an
initial water content of 10%, these times are indicated
in table 4. Unfortunately, this water zone is located
in a
JMDMT 638 Microfossils of Cyanobacteria in Carbonaceous Meteorites Descrição do Vídeo:
The James M. DuPont Meteorite Collection - asteroids
were ever heated by an internal heat source {e.g.,
extinct radioactivity), some temperature distribution
resembling the curves in figure 6 would result. The
surface temperature of the body would be controlled by
the amount of solar radiation reaching it, and might be
around 100 to 200° K. Farther inward, the temperature
would rise until the melting point of ice was reached.
Liquid water could exist in this zone, down to a depth
at which the boiling point at the prevailing pressure
was reached. In FIGURE 7 is shown the locat
JMDMT 637 Microfossils of Cyanobacteria in Carbonaceous Meteorites Descrição do Vídeo:
The James M. DuPont Meteorite Collection - surface
temperature must be high enough to allow liquid water to
exist, but the temperature is controlled not only by the
distance from the sun, but also by the composition of
the atmosphere. If Venus, with its CO-rich atmosphere,
were located in the asteroidal belt, it would have a
comfortable surface temperature near 300° K., instead of
the 600° K. prevailing at its present location. If it
were not for the fact that the planetary hypothesis runs
into so many other ditficulties (Anders and Goles,
1961), one could stop here. Of all th
JMDMT 636 Microfossils of Cyanobacteria in Carbonaceous Meteorites Descrição do Vídeo:
The James M. DuPont Meteorite Collection - gains
further support from the discovery in cosmic dust of
metal flakes with amorphous organic attachments. The
fall dates of these particles seem to be correlated with
several meteor showers of cometary origin (Parkin,
Hunter, and Brownlow, 1962). Perhaps Herbig's (1961)
sug- gestion that the carbonaceous chondrites were
derived from comets should be re-examined in the hght
of this possibility. Aqueous stage and the
prerequisites for life. What about the third question,
the setting in which the aqueous stage took place? This
is o
JMDMT 635 Microfossils of Cyanobacteria in Carbonaceous Meteorites Descrição do Vídeo:
The James M. DuPont Meteorite Collection - on
temperature drop. The further accretion of the (now
cold) dust into solid bodies, and the separation of the
solids from the noncondensable gas would proceed along
the path outlined by Urey (1952, 1954, 1956, 1957,
1958) or Fish et al. (1960). Incidentally, if such a
high-tem- perature stage ever took place, then cometary
matter, too, must have passed through it. This raises
some new possibilities in regard to the mineral com-
position of comets. In particular, the presence in
comet tails of metal (or mag- netite?) spherules, infe
JMDMT 634 Microfossils of Cyanobacteria in Carbonaceous Meteorites Descrição do Vídeo:
The James M. DuPont Meteorite Collection - its
primordial gases completely. It is possible to
accomplish this in the meteorite parent body, but some
special assumptions are required (DuFresne and Anders,
19626). A more 522 Annals New York Academy of Sciences
attractive possibility is offered by Wood's (1958,
1962) hypothesis, according to which planetary matter,
expelled from the sun at high initial temperatures,
cooled by adiabatic expansion, so that progressive
expansion could take place. The least volatile
constituents would condense to high-temperature minerals
(olivine
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JMDMT 622 Microfossils of Cyanobacteria in Carbonaceous Meteorites Descrição do Vídeo:
The James M. DuPont Meteorite Collection -basic
oxides. The CO2 was, in turn, probably evolved from the
interior of the body during reduction of iron oxides to
metallic iron. If the carbonate and mag- netite reached
isotopic ecjuiUbrium during the aqueous stage, the
temperature of this stage may be determined by means of
Urey's paleotemperature method. A clue to the duration
of the aqueous stage is given by the relatively high
degree of ordering of the Ca++ and Mg++ ions in the
dolomite from Orgueil and Ivuna. From a comparison with
terrestrial dolomites. Goldsmith has esti
JMDMT 621 Microfossils of Cyanobacteria in Carbonaceous Meteorites Descrição do Vídeo:
The James M. DuPont Meteorite Collection -much lower
from the fact that the characteristic minerals are
quite finely grained, judging from the diffuseness of
their x-ray diffraction patterns. It seems likely that
the aqueous stage occurred at approximately room
temperature. There is hope of obtaining a more accurate
value by measuring the O'YO'' fractiona- tion between
carbonate and magnetite (Clayton, 1962). Presumably the
Figure 1. A fragment of Orgueil, showing white vein of
magnesium sulfate running hori- zontally across specimen.
This vein must have deposited from wa
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JMDMT 615 Microfossils of Cyanobacteria in Carbonaceous Meteorites Descrição do Vídeo:
The James M. DuPont Meteorite Collection - Fish et
al. (1960); Wood (1958, 1962) Asteroidal 2-5 a.u.
Several Extinct radio- activity Ringwood (1961) Lunar
2-5 a.u. Several Radioactivity Table 2 Origin of
Carbonaceous Chondrites \. High-iron group chondrites
altered by infiltration of water, carbonaceous matter,
and hydrogen sulfide from some other source (Urey,
1961). 2. Primitive material accreted at low
temperatures from solar nebula (Mason, 1960, 1961;
Ringwood, 1961). Other chondrites were derived from
this material by heating and reduction. 3. Primitive
materi
JMDMT 614 Microfossils of Cyanobacteria in Carbonaceous Meteorites Descrição do Vídeo:
The James M. DuPont Meteorite Collection - layer of
exceedingly finely grained, randomly oriented, Murray F
mineral. The common orientation of the olivine plates
can be understood only if single crystal olivine served
as the starting material (Du- Fresne and Anders, 1962a).
Still, one cannot exclude the possibility that some
fraction of the characteristic minerals is primordial,
rather than being derived from the olivine. Many of the
other characteristic minerals, too, seem to be hydrated
silicates. This fact, and particularly the occurrence
of MgS04 in distinct veins (fig
JMDMT 610 Microfossils of Cyanobacteria in Carbonaceous Meteorites Descrição do Vídeo:
The James M. DuPont Meteorite Collection - larger
bodies. To reconstruct their history, we must try to
learn more about the nature of these bodies, that is,
their size, number, and location, and the chemical and
physical processes that produced the de- tailed
structural and compositional features of the meteorites.
Some of the principal hypotheses on the origin of
meteorites are outlined in TABLE 1. (A more complete
review of the subject has been given by Anders and
Goles, 1961.) Each of these hypotheses can account for
some 90 to 95 per cent of the properties of the mete
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