[meteorite-list] NASA Study Shows Asteroids May Have Accelerated Life on Earth

[Ron Baalke]

May 20, 2009

Dwayne Brown 
Headquarters, Washington 
202-358-1726 
dwayne.c.brown at nasa.gov 

Jim Scott 
University of Colorado, Boulder 
303-492-3114 
jim.scott at colorado.edu 

RELEASE: 09-111

NASA STUDY SHOWS ASTEROIDS MAY HAVE ACCELERATED LIFE ON EARTH

WASHINGTON -- A NASA-funded study indicates that an intense asteroid 
bombardment nearly 4 billion years ago may not have sterilized the 
early Earth as completely as previously thought. The asteroids, some 
the size of Kansas, possibly even provided a boost for early life. 

The study focused on a particularly cataclysmic occurrence known as 
the Late Heavy Bombardment, or LHB. This event occurred approximately 
3.9 billion years ago and lasted 20 to 200 million years. In a letter 
published in the May 21 issue of Nature magazine titled "Microbial 
Habitability of the Hadean Earth during the Late Heavy Bombardment," 
Oleg Abramov and Stephen J. Mojzsis, astrobiologists at the 
University of Colorado's Department of Geological Sciences, report on 
the results of a computer modeling project designed to study the 
heating of Earth by the bombardment. 

Results from their project show that while the Late Heavy Bombardment 
might have generated enough heat to sterilize Earth's surface, 
microbial life in subsurface and underwater environments almost 
certainly would have survived. 

"Exactly when life originated on Earth is a hotly debated topic," said 
Michael H. New, the astrobiology discipline scientist and manager of 
the Exobiology and Evolutionary Biology Program at NASA Headquarters 
in Washington. "These findings are significant because they indicate 
that if life had begun before the LHB or some time prior to 4 billion 
years ago, it could have survived in limited refuges and then 
expanded to fill our world." 

"Our new results point to the possibility life could have emerged 
about the same time that evidence for our planet's oceans first 
appears," said Mojzsis, principal investigator of the project. 

A growing scientific consensus is that during our solar system's 
formation, planetary bodies were pummeled by debris throughout the 
Late Heavy Bombardment. A visual record of the event is preserved in 
the form of the scarred face of our moon. On Earth, all traces of the 
bombardment appear to have been erased by rock recycling forces like 
weathering, volcanoes or other conditions that cause the crust to 
move or change. 

Surface habitats for microbial life on early Earth would have been 
destroyed repeatedly by the bombardment. However, at the same time, 
impacts could have created subsurface habitats for life, such as 
extensive networks of cracks or even hydrothermal vents. Any existing 
microbial life on Earth could have found refuge in these habitats. If 
life had not yet emerged on Earth by the time of the bombardment, 
these new subsurface environments could have been the place where 
terrestrial life emerged. 

"Even under the most extreme conditions we imposed on our model, the 
bombardment could not have sterilized Earth completely," said 
Abramov, lead author of the paper. "Our results are in line with the 
scientific consensus that hyperthermophilic, or 'heat-loving,' 
microbes could have been the earliest life forms on Earth, or 
survivors from an even more ancient biosphere. The results also 
support the potential for the persistence of microbial biospheres on 
other planetary bodies whose surfaces were reworked by the 
bombardment, including Mars." 

NASA's Astrobiology Program's Exobiology and Evolutionary Biology 
Program and the NASA Astrobiology Institute at NASA's Ames Research 
Center at Moffett Field, Calif., through its support of NASA's 
Postdoctoral Program, provided funding for this research. The 
Astrobiology Program supports research into the origin, evolution, 
distribution and future of life on Earth and the potential for life 
elsewhere. 

For more information about NASA's astrobiology activities, visit: 

http://astrobiology.nasa.gov 
	
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