Phys.org has an article by the Foundation for Applied Molecular Evolution, “Scientists announce a breakthrough in determining life’s origin on Earth — and maybe Mars.” The article celebrates the experimental results published last month by investigators at the foundation that purportedly represents a breakthrough in origin-of-life research:
Scientists at the Foundation for Applied Molecular Evolution announced today that ribonucleic acid (RNA), an analog of DNA that was likely the first genetic material for life, spontaneously forms on basalt lava glass. Such glass was abundant on Earth 4.35 billion years ago.
The results were published in the journal Astrobiology. Unfortunately, the experiment, upon closer examination, reinforces the opposite conclusion — RNA could never have originated on the early earth without intelligent direction.
The research team attempted to model how nucleotides could combine into long RNA chains on the surface of basalt lava glass. Rock glasses were likely abundant on the early earth, so the investigators claim that this process could have generated abundant RNA, setting the stage for life’s genesis as postulated by the RNA World hypothesis.
The team ground rock glass into a powder and then mixed it with nucleoside triphosphates (NTPs). A nucleoside is a ribose sugar molecule (or deoxyribose for DNA) attached to one of four base groups (A, G, C, or U). The NTP molecules are nucleotides — the building blocks of RNA — with two additional phosphate groups attached to the native phosphate. A standard nucleotide is a ribose sugar attached to a base group and a single phosphate. The team initiated a highly orchestrated experimental protocol that generated RNA-like molecules by binding the nucleotide portion of NTPs to growing nucleotide chains while losing the two additional phosphates.
The Origin of NTPs
The experiment required NTPs with the highly energetic phosphate bonds since standard nucleotides will not spontaneously link together due to the reaction being energetically unfavorable. The key question is how NTPs could have originated. Two of the authors of the recent study published a 2021 article in the same journal purporting to answer this question.
The investigators mixed nucleosides with nickel borate and cyclic trimetaphosphate (CTMP). The CTMP molecule consists of three phosphate groups linked together in a circle. The investigators initiated a highly specified experimental protocol that broke one of the linkages in CTMP and linked the resulting phosphate chain to a nucleoside to generate NPT. The borate prevents the phosphates from chemically bonding to the wrong atoms in the nucleoside. The NTPs could then in principle link together into RNA chains as described in the recent study.
A Soberer Assessment
The chemistry prowess demonstrated in the two studies is certainly impressive. But do the experimental protocols in any way reflect what could have occurred on the early earth? The answer appears to be decisively no.
The 2021 NTP experiment started with nucleoside concentrations corresponding to quadrillions (thousands of trillions) of nucleoside molecules in a volume smaller than a drop of water. Such large concentrations were essential for sufficient NTPs to be generated that could link into RNA molecules at a rate that would outpace RNA degradation. The core challenge is that the synthesis of nucleosides requires exceedingly complex and highly orchestrated chemical steps. Synthetic chemist James Tour details the challenges in his origin-of-life video series (here, here). The chance of even a few hundred nucleobases emerging on the early earth at the same time in the same location is beyond remote.
In addition, the 2021 study required concentrations of CTMP that could never have occurred naturally. Sahai et al. in their 2022 article commented that “the prebiotic availability of cyclic trimetaphosphate is generally considered implausible.” The fundamental problem is that linking nucleotides together to form RNA requires adding specified high-energy bonds (e.g., NTPs). Yet adding specified high-energy bonds requires starting with specified high-free-energy molecules such as CTMP. But generating such specified high-free-energy molecules is exceedingly difficult due to their required specificity and high free energy.
Even if one granted high concentrations of NTPs, the recent study still offers meager support for the RNA World hypothesis. RNA consists of nucleotides joined by what are termed 3’-5’ linkages. But the chains generated in the study also included 2’-5’ linkages as well as additional branching. The problem is that nucleotide chains not consisting of purely 3’-5’ linkages cannot easily be replicated. Leading researcher Jack Szostak has acknowledged that “all known RNA polymerases are highly specific for the synthesis of 3′-5′ linkages…” He hopes that future research might overcome this challenge, but no discovery to date suggests that the problem is surmountable. Consequently, any RNA that did appear would most likely have broken apart within a few months.
An honest evaluation of the two studies leads to the conclusion that the formation of RNA could not have occurred through any natural processes on the early earth. The complex and highly orchestrated experimental protocols with unnatural starting materials further demonstrate that intelligent agency is an essential ingredient to life’s origin.