[meteorite-list] Research Study Determines Life-Producing Phosphorus Was Carried To Earth By Meteorites

[Ron Baalke]

http://news.usf.edu/article/templates/?a=5477&z=210

Solving a 3.5 Billion-Year-Old Mystery

A USF researcher is part of a team that determined life-producing phosphorus 
was carried to Earth by meteorites.
 
By Vickie Chachere
University of South Florida 
June 3, 2013
 
TAMPA, Fla. - Scientists may not know for certain whether life exists 
in outer space, but new research from a team of scientists led by a University 
of South Florida astrobiologist now shows that one key element that produced 
life on Earth  was carried here on meteorites.

In an article published in the new edition of the Proceedings of the National 
Academies of Sciences, USF Assistant Professor of Geology Matthew Pasek 
and researchers from the University of Washington and the Edinburg Centre 
for Carbon Innovation, revealed new findings that explain how the reactive 
phosphorus that was an essential component for creating the earliest life 
forms came to Earth.

The scientists found that during the Hadean and Archean eons - the first 
of the four principal eons of the Earth's earliest history - the heavy 
bombardment of meteorites provided reactive phosphorus that when released 
in water could be incorporated into prebiotic molecules. The scientists 
documented the phosphorus in early Archean limestone, showing it was abundant 
some 3.5 billion years ago.

The scientists concluded that the meteorites delivered phosphorus in minerals 
that are not seen on the surface of the Earth, and these minerals corroded 
in water to release phosphorus in a form seen only on the early Earth.
 
The discovery answers one of the key questions for scientist trying to 
unlock the processes that gave rise to early life forms: Why don't we 
see new life forms today?

"Meteorite phosphorus may have been a fuel that provided the energy and 
phosphorus necessary for the onset of life," said Pasek, who studies the 
chemical composition of space and how it might have contributed to the 
origins of life. "If this meteoritic phosphorus is added to simple organic 
compounds, it can generate phosphorus biomolecules identical to those 
seen in life today."

Pasek said the research provides a plausible answer: The conditions under 
which life arose on the Earth billions of years ago are no longer present 
today. 

"The present research shows that this is indeed the case: Phosphorus chemistry 
on the early Earth was substantially different billions of years ago than 
it is today," he added.

The research team reached their conclusion after examining Earth core 
samples from Australia, Zimbabwe, West Virginia, Wyoming and in Avon Park, 
Florida

Previous research had showed that before the emergence of modern DNA-RNA-protein 
life that is known today, the earliest biological forms evolved from RNA 
alone. What has stumped scientists, however, was understanding how those 
early RNA-based life forms synthesized environmental phosphorus, which 
in its current form is relatively insoluble and unreactive.

Meteorites would have provided reactive phosphorus in the form of the 
iron-nickel phosphide mineral schreibersite, which in water released soluble 
and reactive phosphite. Phosphite is the salt scientists believe could 
have been incorporated into prebiotic molecules.

Of all of the samples analyzed, only the oldest, the Coonterunah carbonate 
samples from the early Archean of Australia, showed the presence of phosphite, 
Other natural sources of phosphite include lightning strikes, geothermal 
fluids  and possibly microbial activity under extremely anaerobic condition, 
but no other terrestrial sources of phosphite have been identified and 
none could have produced the quantities of phosphite needed to be dissolved 
in early Earth oceans that gave rise to life, the researchers concluded.
 
The scientists said meteorite phosphite would have been abundant enough 
to adjust the chemistry of the oceans, with its chemical signature later 
becoming trapped in marine carbonate where it was preserved.

It is still possible, the researchers noted, that other natural sources 
of phosphite could be identified, such as in hydrothermal systems. While 
that might lead to reducing the total meteoric mass necessary to provide 
enough phosphite, the researchers said more work would need to be done 
to determine the exact contribution of separate sources to what they are 
certain was an essential ingredient to early life.