[meteorite-list] Geologists Focus on Mineral for Clues to Beginning of Biological Life

[Ron Baalke]

http://www.eurekalert.org/pub_releases/2015-12/uosf-ugf121515.php

Public Release: 16-Dec-2015

USF geologists focus on mineral for clues to beginning of biological life 
on earth

In Earth's beginning, meteorites striking the planet to provide light 
may have carried an extraterrestrial mineral that, as it corroded in water, 
could have provided the essential chemical spark for the birth of biological 
life

On the early Earth, light came not only from the sun but also from the 
incessant bombardment of fireball meteorites continually striking the 
planet. Now, the recent work of University of South Florida (USF) associate 
professor of geology Matthew Pasek, USF researcher Maheen Gull, and colleagues 
at Georgia Institute of Technology, has demonstrated that these meteorites 
may have carried within them an extraterrestrial mineral that, as it corroded 
in water on Earth, could have provided the essential chemical spark leading 
to the birth of biological life on the planet.

In previous work, Pasek and colleagues suggested that the ancient meteorites 
contained the iron-nickel phosphide mineral "schreibersite," and that 
when schreibersite came into contact with Earth's watery environment a 
phosphate, a salt, was released that scientists believe could have played 
a role in the development of "prebiotic" molecules.

In a recent study appearing in Nature Publishing Group's Scientific Reports, 
the researchers focused on the properties of schreibersite and conducted 
experiments with the mineral to better understand how - in a chemical 
reaction with the corrosive effects of water called "phosphorylation" 
- schreibersite could have provided the phosphate important to the emergence 
of early biological life.

"Up to ten percent of the Earth's crustal phosphate may have originated 
from schreibersite, so the mineral was abundant and readily available 
to engage in early chemical reactions," said Pasek. "This ready and abundant 
source of reactive phosphorous may have been an important part of the 
prebiotic Earth and possibly the planet Mars," said Pasek.

What needed to be determined, however, was just how schreibersite reacted 
chemically with the early Earth's watery environment and what resulted 
from the chemical reaction.

To test their hypothesis, they built an early Earth model environment, 
an organic-rich aqueous solution in which schreibersite might react and 
corrode in a way similar to how events may have unfolded in prebiotic 
chemistry. The model they constructed provided an opportunity to observe 
the thermodynamics of phosphorylation reactions of a phosphorus-containing 
synthetic schreibersite, which they created to be structurally identical 
to its meteorite counterpart.

"A thorough exploration of the extent of phosphorylation of nucleosides 
(made of a base and a five carbon sugar) by schreibersite was necessary 
to evaluate its potential prebiotic importance," explained Gull, a post-doctoral 
fellow and visiting researcher at USF. "All of our experiments indicated 
that a basic pH, rather than acidic pH, was required for the production 
of phosphorylated products. Although phosphorylation can take place using 
a variety of phosphate minerals in non-aqueous solution, prebiotic oxidation 
in water is more likely given the dominance of water across the solar 
system."

The prebiotic reaction they duplicated in the laboratory may have been 
similar to the reactions that ultimately led to the emergence of metabolic 
molecules, such as adenosine triphosphate (ATP), which is called the 'molecule 
of life' because it is central to energy metabolism in all life.

Pasek and Gull also explained that even life today builds from activated 
nucleotides and that phosphates are still an important part of metabolic 
processes in biological life, so it is likely that a phosphorylated biomolecule 
played an important part in creating the prebiotic chemical context from 
which biological life emerged. Prior work on nucleoside phosphorylation 
has shown that inorganic phosphate can serve as both a catalyst and a 
reactant in nucleoside synthesis, they said.

"The reactions we observed in our experiments have shown that the necessary 
prebiotic molecules were likely present on the early Earth and that the 
Earth was predisposed to phosphorylated biomolecules," the researchers 
concluded. "Our results suggest a potential role for meteoritic phosphorus 
in the development and origin of early life."

The researchers also concluded that the mechanism of phosphorylation was 
still unknown and actively being investigated. "It is possible that the 
process occurs in solution or on the surface of the schreibersite," they 
explained.

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