Phosphorus carried to Earth by meteorites
Washington: A team of scientists has finally solved a 3.5 billion-year-old mystery showing that phosphorus - key element that produced life on Earth- was carried to Earth on meteorites.
The scientists led by a University of South Florida astrobiologist 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.
USF Assistant Professor of Geology Matthew Pasek and researchers from the University of Washington and the Edinburg Centre for Carbon Innovation documented the phosphorus in early Archean limestone, showing it was abundant some 3.5 billion years ago.
They 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.
Pasek, who studies the chemical composition of space and how it might have contributed to the origins of life, said 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.
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.
The results appeared in an article published in the new edition of the Proceedings of the National Academies of Sciences.
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