RE: Vida en Marte: nuevos experimentos.

["Gonzalo J. Perez" <gonj@...>]

> De: Javier <ssta en lix.intercom.es>
> GONZALO: TE AGRADECERE QUE ME

	Uy, perdon, ... no es exactamente asi, dije una cosa que no era. El
oxigeno no proviene del que esta contenido en la materia organica, es otra
cosa. (El origen de la confusion es muy tonto: al leer eso de 'surges' lo
traduje por bombeo; esto es debido a que suelo ver la palabra asociada a un
tipo de inestabilidad que se da en los compresores, pero que en espanyol se
llama bombeo, aunque lo normal es que se use la palabra inglesa. (He mirado
el diccionario y ya he visto que una cosa no es traducion literal de la
otra)). Y claro, al entender eso del bombeo de oxigeno a la atmosfera, y
mas adelante lo del almacenamiento de carbono organico... Pido disculpas
por la metedura de pata. Si no me equivoco, lo que DesMarais dice que
ocurre es que, al estar la materia organica enterrada, el equilibrio que el
dice respiracion-fotosintesis se rompio, porque la materia organica es
consumida por las bacterias en la respiracion para producir CO2, de manera
que la 'cantidad' de respiracion no fue capaz de consumir todo el oxigeno
para mantener la concentracion inicial, y esta aumento. Pongo la nota de
prensa, y asi nos ahorramos complicaciones de errores de interpretacion. De
todas maneras, advierto que yo no tengo nada que ver con DesMarais, y no
pienso defender ni rebatir su hipotesis, porque no es mi campo y entiendo
mas bien poco tirando a nada de estas cosas, asi que me fio del, digamos,
'debate cientifico habitual'. Solo lo cuento porque me parece interesante:

RELEASE:  96-219

RESEARCH SUGGESTS MOST OF EARTH'S OXYGEN 
SUPPLY WAS PRODUCED BY GEOLOGIC EVENTS

       Refined calculations and new evidence support a 
revolutionary suggestion that global-scale geologic events 
produced the bulk of Earth's oxygen supply, a NASA scientist 
reported today. 

       Scientists have long believed that oxygen collected in 
Earth's early atmosphere as a by-product of plant life from a 
process called photosynthesis, in which plants take carbon 
dioxide and water to produce organic matter and oxygen.  Dr. 
David DesMarais, of NASA's Ames Research Center, Mountain 
View, CA, first suggested in 1992 a relationship between 
oxygen and the collision of continents, the resultant 
colossal mountain ranges and increased erosion burying huge 
amounts of organic matter in ocean beds.

       "Although photosynthesis did provide an oxygen source 
strong enough to sustain the amount of existing oxygen, the 
creation and assembly of large modern-sized continents was 
responsible for early dramatic increases in oxygen," 
DesMarais said.

       DesMarais today reported new evidence supporting his 
findings at the Geological Society of America meeting in Denver. 

       DesMarais' research correlates oxygen "surges" in the 
atmosphere 2.2 to 2.0 billion years ago with changes in the 
amount of carbon stored in Earth's crust at that time.  
During that time, several of Earth's "micro" continents 
crashed together forming new, stable modern-sized continents.  
As the continental fragments collided, towering mountain 
ranges formed.  Their steep slopes produced rapid erosion and 
sedimentation, key to DesMarais' theory.

       Organic matter is normally consumed by bacteria and 
animals, a process that utilizes oxygen (respiration), 
producing energy and carbon dioxide and water as by-products.  
According to DesMarais, when huge amounts of organic matter 
were buried during cataclysmic collisions, oxygen was freed 
to accumulate in Earth's early atmosphere. 

       "The cycle of photosynthesis (which produces oxygen) 
and respiration (where oxygen is consumed) is an almost 
break-even process," DesMarais said.  Only when large amounts 
of organic material are buried in ocean sediments during 
tectonic upheavals can the amount of oxygen in the atmosphere 
increase substantially, he added.

       An independent recent study concludes that 
approximately three large continental masses were assembled 
between 2.5 and 1.9 billion years ago by the collision of 
smaller land masses.  Two of these were assembled between 2.2 
and 1.9 billion years ago.  These collisions formed 
Himalayan-class mountains with high rates of sedimentation in 
the ocean, burying organic matter.

       According to DesMarais, the formation of stable, large 
continents also protects and stores larger amounts of organic 
carbon for hundreds of millions of years, further allowing 
the atmosphere to accumulate large amounts of free oxygen.

       Furthermore, new calculations by DesMarais reveal that 
the increases in atmospheric oxygen and sulfate (oxidized 
sulfur) in seawater, between 2.2 and 2.0 billion years ago 
were too large to be explained only by the slow decline in 
volcanic activity over Earth's history.  The decline in 
volcanism had been previously offered as an alternative to 
DesMarais' continental evolution hypothesis.

       DesMarais' research is supported by the space science 
division at the Ames Research Center and the Exobiology 
Program in NASA's Office of Space Science, Headquarters, 
Washington, DC.

                          -end-

	
	Saludos
	Gonzalo J. Perez
	gonj en ctv.es