eli@spdcc.COM (Steve Elias) (05/03/88)
here's a bit from the notes i've located from Frank Drake's class:
"Life in the Universe". followups to sci.misc.
first, his concluding statement, which some of you have disagreed with, when
i brought it up a month or so ago...
"although we have a good idea of factors involved, the problem of climatic
evolution is too complicated to solve with any useful accuracy! alas!"
here is more from his lecture on the greenhouse effect, transcribed
verbatim from the lecture notes he prepared:
the greenhouse effect:
caused by the selective transmission of thermal radiation.
can cause a surface to be coler or warmer than it would be otherwise.
in solar system, "greenhouses" everywhere are fortuitously such that they
selectively admit sunlight, and trap infrared radiation emitted by surface.
this leads to substantial warming.
if the temperature gets high enough, a vicious cycle develops:
- much water vapor is evaporated from ocean - it enhances greenhouse -
- more water vapor is evaporated / CO2 is increased / temp goes up -
- process repeats - eventually boiling point of water is reached /
all oceans and lakes evaporate (300 bar on earth) - temp remains high.
it may have happened on venus.
earth is only 25 degrees or so away from a runaway greenhouse.
---- the rest of the 'greenhouse effect' lecture is summarized below.
---- i'll post more on any given section if anyone gives a hoot.
---- other lectures include: the Drake equation, paths to the molecules
---- of life, stars, radio theory, dyson spheres, practical considerations
---- for interstellar rockets...
(Prof. Drake then goes on to explain "the ice catastrophe" -- a runaway
global chill-out... planet gets ice-covered -- reflects almost all light).
(next -- he talks about the glaciers and the history of the sun's
brightness, and explains why the 'ice catastrophe' didn't happen.)
(then the recent thermal history of earth -- temp nearly follows assumed
increase in CO2 due to industrial activity).
some less important factors affecting climatic evolution:
1 - timing of perihelion with seasons -- 26000 year period
2 - change in tilt of planet's axis -- 4 degrees per 40000 years
3 - change in ellipticity of orbit -- 100,000 year period
(the above 3 factors give the "Milankovitch" periods & hypothesis).
4 - solar activity
5 - amount of land surface / ocean surface
6 - patterns of ocean currents (they moderate climate)
7 - particulate matter in atmosphere -- cools planet (remember 1817)
8 - amount of ice deposits
9 - amount of cloud cover -- higher temps give less clouds -- clouds can
either warm or cool on average.
10 -- the presence of life -- can change albedo (plants good absorbers)
can change atmosphere, plants reduced CO2, added O2, reduce g.h. effect.
question: does life act to stabilize conditions so they are suitable for life?
this is the "Gaia" hypothesis of Margolis & Lovelock. most doubt the control/
feedback is so profound...
(finally, Drake discusses the 'continously habitable zone' -- the radius
around a star at which life-giving temperatures can be maintained.)
one study (Michael Hart) computed that the radius for our sun is
between .95 and 1.01 AU... (there were some miscalculations in the study.)
--- that's it for this lecture -- he concludes with the statement at the
--- start of the posting...jsf@rlgvax.UUCP (Steve Fritzinger) (05/03/88)
In article <1012@spdcc.COM>, eli@spdcc.COM (Steve Elias) writes: > some less important factors affecting climatic evolution: > . . . > 10 -- the presence of life -- can change albedo (plants good absorbers) > can change atmosphere, plants reduced CO2, added O2, reduce g.h. effect. > > question: does life act to stabilize conditions so they are suitable for life? > this is the "Gaia" hypothesis of Margolis & Lovelock. most doubt the control/ > feedback is so profound... > > (finally, Drake discusses the 'continously habitable zone' -- the radius > around a star at which life-giving temperatures can be maintained.) > > one study (Michael Hart) computed that the radius for our sun is > between .95 and 1.01 AU... (there were some miscalculations in the study.) The February 1988 issue of Scientific American contains an article on the Goldilocks Problem (Why is Mars too cold, Venus too hot and the Earth just right?) The authors propose that geological proccesses, and the oceans form an active feedback loop that regulates the Earth's temperature. Basically rain washes CO2 out of the atmosphere and into the ocean where it is bound into CaCo3. Subduction eventually drives the CaCO3 rich layer under a continental plate, where it is heated and the CO2 released. If the climate becomes hotter, there is more rain, which removes CO2 from the atmosphere, cooling the planet. Conversely if the climate cools off there is less rain, resulting in a CO2 build up, and a warming trend. The authors estimate that given current rates of CO2 release, if the oceans ever completely froze over (stopping rainfall, and allowing a rapid CO2 build up) the resulting greenhouse would return the planet's temp. to about 50 deg C. in 20 million years. The article also explains how this model could have failed on Mars resulting in a cold frozen world, and on Venus causing it's runaway Greenhouse. In a letter to the editor in the April issue a reader whimsically answers the Goldilocks Problem with "Because Earthlings are asking the question." -- Steve Fritzinger CCI-OSD Reston VA. uunet!rlgvax!jsf Who's the monster that's really swell? G-R-E-N-D-E-L What's the thing that he does best? N-E-M-E-S-I-S