One of my favorite blues tunes is "Born Under a Bad Sign," a song about someone who just can't catch a break.
If there is a scientific discipline that is characterized by "havin' bad luck all of [its] days," it's origin-of-life research. This trend of bad luck continues for a collaborative team from the University of South Florida (USF) and the Georgia Institute of Technology (GT) who are seeking to identify a chemical process that could produce organic phosphates on early Earth, a necessary step in any origin-of-life scenario. Ironically, in their attempts to support a naturalistic origin-of-life scenario, these researchers have demonstrated the critical role an intelligent agency must play in life's genesis.
The emergence of organic phosphates stands as one of the most significant challenges facing any naturalistic origin-of-life scenario. Organic phosphates include DNA; RNA;the biomolecules that form cell membranes; and ATP, the compound that serves as the cell's energy currency.
The Problem of Organic Phosphates
Phosphorylation reactions are the chemical processes that generate organic phosphates in the cell. Phosphorylation occurs when enzymes catalyze the addition of phosphate groups to a target molecule. One conceivable way that phosphorylation could have happened during abiogenesis is through the direct addition of a phosphate group to prebiotic molecules. However, this reaction doesn't take place readily in water—it requires dehydrating conditions and relatively high temperatures.
Origin-of-life researchers aren't sure where these types of conditions would exist on early Earth. Additionally, they are concerned that high temperatures would have caused fragile prebiotic materials to break down. Another problem origin-of-life researchers have identified with this chemical route relates to phosphates' solubility. These compounds tend to be highly insoluble in the presence of calcium and magnesium ions, both of which would have been abundant in early Earth's oceans. The insolubility of calcium and magnesium phosphates would have rendered these compounds unavailable for any prebiotic reactions. (For a more complete discussion of the problems associated with generating organic phosphates on early Earth see my book Creating Life in the Lab.)
Have Researchers Found a Solution?
A few years ago, the team from USF proposed a way around these problems. They suggested that organic phosphates could be produced from the iron phosphide and iron-nickel phosphide composing schreibersite (a mineral found in meteorites).1 The USF scientists speculated that abundant schreibersite would have been delivered to early Earth when the planet was pummeled with asteroids during its early history. To confirm their suspicion, these researchers analyzed carbonate minerals from a geological formation in Australia that dates to around 3.5 billion years ago. The team identified phosphites in the carbonate minerals at levels that indicated these minerals would have been a prominent species in early Earth's oceans. Phosphites do not have a biological origin and the phosphites in the carbonate minerals were most likely generated from the phosphides in schreibersite.
Phosphites are much more chemically reactive than phosphates and can phosphorylate organic materials in water. This makes them—and schreibersite—a potential source of phosphorus for phosphorylation reactions on early Earth.
To confirm that schreibersite could, indeed, phosphorylate organic compounds, the researchers heated an aqueous solution of glycerol and schreibersite to 150°F for two days. Afterwards, they found phosphite in the solution along with low levels of glycerol phosphate.
In a follow-up study, the USF team, in collaboration with researchers from GT, assessed whether or not schreibersite could phosphorylate adenosine and uridinenucleosides. The phosphorylated forms of these molecules comprise two of the four building blocks of RNA.2 These building block materials factor significantly into the RNA world hypothesis, one of the most important origin-of-life scenarios. The scientists showed that these two nucleosides could be phosphorylated when heated with schreibersite for several days at 175°F, when the solution was slightly alkaline. They even showed that this reaction would proceed in the presence of magnesium ions.
Based on these two studies, the researchers posit that they have made significant strides towards understanding how organic phosphates formed on early Earth and provided support for chemical evolution and abiogenesis: