Two World's encounter.

We have previously stated the possibility to promote or, find life in Titan either transporting it there, by cultural reasons or, arising de novo in this moon. One reason for the late statemente is the existence of CH4 (methane) in its atmosphere.If the sunrays destroys CH4, what reasons explains its persistence?.Are there ancient microorganisms under its visible floor?.Pace (1997:734-40), has noted that Metanococus janschii(an arqueobacteriae) emits CH4 as a final by product, on Earth.

We don't know exactly the methods that clean machines and astronauts when they return to Earth, after landing in extraterrestrial grounds.Anyway, in this context one thing is important:the arqueobacteriae can resist any conventional cleaning's procedure.

If microorganisms of other worlds contaminate Earth's people there are two possibilities : 1- It happens nothing(because their inmune systems are similar) or, 2-The foreign microbes destroy any kind of clonal (most of all) and non clonal life's descent who were not exposed previously to them.

If you don't believe this, remember what happened to the native inhabitants of the New World, when the spaniards conquered them in 1492.The population of the Incas :12 millions (Cook,1977:37-60)and that of Central Mexico :25 millions (Borah and Cook,1963),dropped to 1 and 3 millions, 100 hundreds years later, respectively (Smith,1968:77).The deaths were caused by differents causes:war,desnutrition,social disruption and diseases (Verano and Ubelaker,1992:15-24).Certain virus like :measles, influenzae and others reached epidemic proportions.The spaniards who arrived to North and South america were the survivors of these diseases, so it happened nothing to them. On the contrary the natives were an unusually homogeneous and virgin populations never exposed to these microbes.This first encounter killed most of them.This was the encounter of two infection's patterns, two inmune heritages, two human groups(organisms)(Black,1992:1739-40).

It is the same actually with the AIDS virus. The people who until now has died is the first generation of human beeings exposed to this virus.It will happens the same also in the near future with exposures to others (new) microbes, which as we know mutate at faster pace than we can.Certainly we need more time to acccomodate our inmune systems to these changes.

Bibliography

1-Pace,Norman.1997.A molecular View of microbial diversity and the biosphere.Science.276:734-40.2-Cook,Noble,David.1977.Estimaciones sobre la Población del Perú en el momento de la Conquista.Histórica-Peru:1(1):37-60. 3-Borah, W and Cook, FS.1963.The aboriginal population of central Mexico on the Eve of the spanish Conquest.Berkeley Press University. 4-Black,FL.1992.Why did they die?.Science.258(88):1739-40. 5-Smith, CT.1968.Despoblación de los andes centrales en el siglo XVI. Revista del Museo Nacional-Perú-.35:77-92. 6-Verano JW and Ubelaker,D.1992. Disease and Demography in prehistoric andean south american people,pp:15-24.In:Disease and Demography in the Americas.Verano JW and Ubelaker,D(editors).Smithsonian Institution Press,Washington.