June 4th, 2013 by James Ayre
Phosphorus — an element essential to life as we know it — is only present on the surface of the Earth as a result of being brought here by meteorites, according to new research. The finding doesn’t offer any answers with regards to the question of whether or not life originated on the Earth, or was brought here by meteorites, but it does make it clear that without meteorites that life as we know it couldn’t live here.
The new research — from the University of South Florida, the University of Washington and the Edinburg Centre for Carbon Innovation — has uncovered a solid explanation for “how the reactive phosphorus that was an essential component for creating the earliest life forms came to Earth.”
The researchers discovered that “during the Hadean and Archean eons — the first of the four principal eons of 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.”
They then came to the conclusion that the “meteorites delivered phosphorus in minerals that are not seen on the surface of Earth, and these minerals corroded in water to release phosphorus in a form seen only on the early Earth.”
The new findings propose an interesting answer to one of the primary questions that researchers in the field having been asking for years — 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 USF Assistant Professor of Geology Matthew 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.”
“The conditions under which life arose on 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 noted.
This conclusion was reached after the examination of core samples from around the world — from Australia, Zimbabwe, West Virginia, Wyoming and Avon Park in Florida.
The press release continues:
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 fluidsand 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 researchers have stated that they think that because of the large numbers of meteorite collisions at the time, that enough phosphite would have been present to change the chemistry of the oceans — the chemical signature of this change then leaving a record of itself in the marine carbonate of the Coonterunah samples.
The researchers note, though, “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 new research was recently published in the Proceedings of the National Academy of Sciences.
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