From SETI - chances of finding another planet capable of sustaining life - anywhere in the Universe has been decreased to 1 in 10 ^ 20 against, making the Earth incredibly unique!
Also I read the other day that the chances of our Universe have the physical constants so well tuned so as to permit intelligent life are - wait for it 1 : 10 ^ 42,000 - by comparision their are 10 ^ 120 atoms in the entire universe. So The chances for life in the Universe by random chace and evolution alone are the same as a class 5 tornado hitting a metal junk with all the componets of a 747 strewn around and exactly assembling it so that is perfectly assembled ready for flight!
Makes you feel special doesn't it?
http://www.konkyo.org/english/seti.html
-extract
Astronomical Parameters Related to Life Supportability on a Planet
1. Galaxy type (.1)
If too elliptical (and therefore not spiral), star formation would have ceased before sufficient heavy elements could be produced and incorporated into a planet to support life chemistry.
If too irregular, radiation exposure on occasion would be too severe and heavy elements for life chemistry would not be available in sufficient quantities.
2. Galaxy size (.1)
If too small, the gravitational field of the galaxy will be too weak to hold on to most of the heavy elements produced in supernova explosions. The inertia of the ejected particles will carry most of them into intergalactic space, making them unavailable for later planetary formation.
If too large, radiation levels will be too high for advanced life.
3. Supernova rates and proximity (.01)
If too close or too frequent or too late in the development of a galaxy, life on a planet would be exterminated by radiation.
If too far away or too infrequent or too soon in the development of a galaxy, not enough heavy elements would be available at the time a planet forms for it to later be able to support life.
White dwarf binaries (a hot dwarf star revolving around a larger star companion). These stars are the only place in the universe where there exists the kind of nuclear reaction necessary to produce the element
3. fluorine, which is also necessary for life chemistry. (.05)
If too few, insufficient fluorine would be produced to later be incorporated into a planet to allow life chemistry to proceed.
If too many, that would mean that the stellar density is so great that planetary orbits would be disrupted and life could not be maintained for long periods of time.
If too early in the development of a galaxy, not enough heavy elements would have been available for efficient fluorine production.
If too late in the development of a galaxy, fluorine would have been produced too late to be available for incorporation into a developing planet.
Parent star location. For a variety of reasons, only stars located between the spiral arms of a galaxy could have a life-supporting planet. Likewise, the system must be at the co-rotational radius in order to maintain its
4. favored position. (.00001)
If located within a spiral arm, high stellar density would increase radiation and lead to destabilization of planetary orbits.
If much farther out than our sun, the quantities of heavy elements necessary to make a planet like earth would have been insufficient and the star would eventually get swept into a spiral arm as it caught up with the star.
If much closer in than our sun, it would also be impossible to maintain a favorable location for long, as the star would again be swept up into a high stellar density arm.
Amplitude of vertical motion away from the galactic plane as a stellar
5. system revolves around the galactic center. (.1)
If great enough to carry the system out of line with the rather narrow band of dust clouds that shield a system from the extreme radiation emitted from the galactic core, radiation levels would greatly rise during the twice per revolution period (about every 100 million years) when the star would be outside the protective zone. Such exposure would be catastrophic to advanced life. The sun is one of the relatively few stars that always remains close to the galactic plane.
6. Number of stars in the planetary system. (.2)
Any planet that is revolving around a double star could not maintain a stable orbit, and thus could not support life.
Likewise, a planet not revolving around any star would obviously be far too cold for life. Therefore, there must be one and only one star around which the planet revolves.
7. Parent star birth date with respect to the parent galaxy. (.2)
If much more recent than our sun, the star would not have been in its stable burning phase for a long enough period to support advance life.
If significantly older than our sun (and therefore a star that developed early in the life of the galaxy), there would not have been enough heavy elements available for the formation of an earth-like planet.
8. Parent star age. (.4)
If either much older or much younger than our sun, the star would not be in a stable burning period and the luminosity of the star would change too quickly.
9. Parent star mass.(.001)
If slightly greater than our sun, the star would burn too rapidly and the luminosity would be too unstable. If slightly less than our sun, the range of distances a life-supporting planet could be from the star would become too narrow; and if such a planet were at that exact distance for proper temperature, the tidal forces involved would be so great that the rotational period of the planet would be slowed down much too fast.
Parent star color (which is dependent on surface temperature). (.4)
If either redder (cooler) or bluer (hotter) than our sun, the "bell curve" that represents the radiation coming from the star would be shifted one way or the other. The entire process involved in plants producing food through photosynthesis would be negatively affected, as the percentage of visible light within the total amount of radiation energy (which must be the same in order to have the same temperature on the planet's surface) would be reduced, thus making photosynthesis less efficient. Also, a certain amount of UV light is necessary. This would be significantly reduced with a cooler sun (leading to reduced efficiency in the production of certain nutrients) and significantly increased with a hotter sun (leading to cell damage). (This also, of course, is affected by the ozone shield).
10. Parent star luminosity relative to the introduction of new life forms on a planet. (.0001)
If the rate of introduction of life forms that decreased the greenhouse effect were too slow, the increase in luminosity would have resulted in a runaway greenhouse effect.
If the rate were too fast, then the too rapid reduction in the greenhouse effect would have resulted in runaway glaciation.
11. Albedo (ratio of reflected light to total amount of radiant energy impinging on the surface) (.1)
If significantly greater than the earth's, runaway glaciation would develop.
If significantly less than the earth's, runaway greenhouse effect would develop.
12. Distance from parent star (.001)
If slightly farther out, the planet would become too cold to maintain a stable water cycle (also resulting in runaway glaciation).
If slightly closer, the planet would be too hot to maintain a stable water cycle (also resulting in runaway greenhouse effect).
13. Surface gravity (escape velocity) (.001)
If stronger, the planet's atmosphere would retain too much ammonia and methane, both of which would be detrimental to life.
If weaker, the planet's atmosphere would loose too much water.
14. Orbital eccentricity (.3)
If much more than the 1.6% it is, seasonal temperature differences would become too extreme.
15. Axial tilt (.3)
If much greater than the ideal of 23.5 degrees, the surface temperature differences between summer and winter for most of the planet would be too extreme for advanced life.
If much less than 23.5 degrees, the regions of the earth with climates suitable for advanced life would be greatly narrowed.
16. Rotation period (.1)
If much longer than 24 hours, the diurnal temperature differences would be too great.
If much shorter, atmospheric wind velocities would be too great, as the forces that drive the winds become much stronger.
17. Age of the planet (?)
If too young, the rotation period would be too fast for all but primitive life.
If too old, the rotation period would have been braked by tidal interaction to the point where it would be too long.
18. Collision rate with asteroids and comets during early and subsequent periods of planet's history (.1)
If much greater than earth, there would be too much destruction of habitat and too many species would become extinct.
If much less than earth, the planet would have received too little of the heavier elements necessary for life. In other words, the planet must have high levels of outside material coming in during its early history, and much less later on.
19. Magnetic field of the planet (.01)
If too strong, electromagnetic storms would be too severe (i.e., they themselves, along with a too powerful van Allen Belt, would become sources of detrimental radiation).
If too weak, life on land would be inadequately protected from hard stellar and solar radiation.
20. Gravitational interaction with a moon (.1)
If much greater than that between the earth and its moon, the tidal effects on the oceans, atmosphere, and rotational period would be too severe.
If much less, instabilities in the rotational axis of the earth would cause climatic instabilities; the movement of nutrients in coastal regions would be insufficient.
21. Thickness of the crust (.01)
If much thicker than the earth, too much oxygen would be absorbed in oxidation and then fixed in the crust without being available for recycling within the atmosphere. The crust can be thought of as a layer of "rust" covering the earth. If too much oxygen is taken up into this "rust", then too little is available for the atmosphere in the form of C0 2, H2O or 0 2. Likewise, plate tectonics would not operate efficiently.
If much thinner than the earth, volcanic and tectonic activity (the movement of plates that cause earthquakes) would become too intense for advanced life to thrive.
22. Oxygen quantity in atmosphere (.01)
If much greater than 21%, organic material would burn up too easily (fires would start and get out of control much too frequently).
If much less than 21%, advanced animals would have too little to breathe.
23. Oxygen to nitrogen ratio in atmosphere (.1)
If much larger, advanced life chemistry would proceed too quickly
If much smaller, advanced life chemistry would proceed too slowly.
24. Carbon dioxide level in atmosphere (.01)
If much higher, a runaway greenhouse effect would develop.
If much lower, plants would be unable to maintain efficient photosynthesis.
25. Water vapor level in atmosphere (.01)
If much higher, a runaway greenhouse effect would develop.
If much lower, rainfall would be too sparse for advanced life on land.
26. Atmospheric electric discharge rate (.1)
If much greater, too much fire destruction would occur.
If much less, too little nitrogen would be transferred from the air to the soil.
27. Ozone level in upper atmosphere (.01)
If too high, surface temperatures would be lower, restricting life zones.
If too low, surface temperatures would rise and more importantly, increased UV radiation would be harmful to life.
28. Soil mineralization (.1)
If either too nutrient poor or too nutrient rich, the diversity and complexity of life forms becomes more limited.
29. Seismic activity(.1)
If too intense, the impact on advanced life forms would be too devastating.
If too weak, nutrients on ocean floors (from river runoff) would not be recycled to the continents through tectonic uplift.
30. Oceans-to-continents ratio (.2)
If either much greater or much smaller than the roughly 3 to 1 ratio of earth, the diversity and complexity of life forms becomes much more restricted.
31. Global distribution of continents on earth (.3)
Having considerably more land area in the Northern Hemisphere than in the Southern Hemisphere helps to balance the effects of the eccentricity of the earth's orbit, with its perihelion in January and its aphelion in July. At the perihelion maximum, the northern hemisphere winter (southern hemisphere summer) receives about 6.7% more solar energy than the southern hemisphere winter (northern hemisphere summer) receives at the aphelion minimum. This difference is compensated for by the moderation of the larger oceans in the south. If a considerably larger portion of the earth's land were in the Southern Hemisphere, increased seasonal temperature variations in both hemispheres would severely restrict appropriate habitats for many forms of life.
Probability of all necessary parameters occurring on one planet
In order to calculate the probability for the existence of other life supporting planets in the universe, at least two other factors must be taken into account. First of all, it needs to be recognized that a number of the above parameters are interdependent, and thus a simple multiplication of individual probabilities will give too low a figure. Thus, a dependency factor needs to be added in.
On the other hand, the dependency factor is at least partially canceled out by a longevity factor, in that all of the parameters must be maintained within acceptable limits for very long periods of time. In the case of the earth, that means almost 4 billion years!
How large are these factors? Dr. Hugh Ross uses in his estimates 10 ^ 9 for the dependency factor and .0001 for the longevity factor. Putting all of these factors together, that means that the probability of the 33 parameters mentioned above that have estimated probability factors to all come together in one planet comes out to one in 10 ^ 42 (or 10 ^ -42)! As there are a number of other parameters being researched for their sensitivity to the support of life on a planet at the probability of finding a Jupiter-like planet as part of a planetary system and numerous other factors not included in the figures above), the odds are probably many orders of magnitude worse! Even if one is generous and makes the dependency factor a million times greater the odds still only rise to 10 ^ -36!
As there are at the most only approximately 10 ^ 23 stars in the entire universe, it becomes quite obvious that the odds of finding even one star with a life supporting planet is very small - about 10^ -20 according to the probabilities listed above. One can, of course, argue with some of the probability estimates for specific parameters, as different scientists using different assumptions and rationales will no doubt come out with different probabilities for at least some of the planetary parameters. The figures used above are, according to Dr. Ross, rather optimistic figures, and thus the probability is high that many of these parameters are even further restrictive. Likewise, it should be added that while we can directly observe only the 9 planets of our own solar system, we have literally trillions of stars that we can observe and make measurements on. Thus, the figures for the stellar parameters are far more certain.
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