In 2006, in a debate with Stephen Meyer, evolutionary paleontologist Peter Ward observed that, “Harvard University just put a hundred million dollars into a center for the origin of life,” and predicted that because origin of life research is “one of the hottest scientific areas in the world we will have artificial life I predict in a decade.” Ten years later, in 2016, also in a debate with Steve Meyer (and Denis Lamoureux), physicist Lawrence Krauss promised “We’re coming very close” to explaining the origin of life via chemical evolutionary models. We’re now 15 years out from the Meyer-Ward debate and nearly five years past the Meyer-Krauss-Lamoureux event. How are these promises of origin-of-life research faring?
At the end of last year, an article in Nature titled “The Water Paradox and the Origins of Life” admitted that there are still major problems facing some of the most basic steps in the origin of life: explaining how the first biomolecules arose in a prebiotic world. The article begins with the tagline: “Water is essential for life, but it breaks down DNA and other key molecules. So how did the first cells deal with such a necessary and dangerous substance?” The article then recounts origin of life theorists on different sides of a debate: some believe that life originated in an ocean, and others believe that life formed at the surface of the earth. What comes through clearly is that the field can’t even agree on the environment where life originated, a disagreement that stems directly from deep problems facing each proposal.
Falling Out of Favor
Since Stanley Miller’s prebiotic synthesis experiments in the 1950s, origin of life theorists have typically proposed that life originated in an oceanic environment. The article explains, however, that this model is now falling out of favor in some quarters:
But many scientists today say there’s a fundamental problem with that idea: life’s cornerstone molecules break down in water. This is because proteins, and nucleic acids such as DNA and RNA, are vulnerable at their joints. Proteins are made of chains of amino acids, and nucleic acids are chains of nucleotides. If the chains are placed in water, it attacks the links and eventually breaks them. In carbon chemistry, “water is an enemy to be excluded as rigorously as possible”, wrote the late biochemist Robert Shapiro in his totemic 1986 book Origins, which critiqued the primordial ocean hypothesis.
This is the water paradox.
To elaborate on the “paradox,” assume for a moment that there was some way to produce simple organic molecules (monomers) on the early earth. Perhaps these molecules formed in an oceanic “soup,” perhaps in the ocean near some high-energy hydrothermal vent. Whatever the case, the next step is to link those molecules into chains, called polymers. However, chemically speaking, the last place you’d want to link amino acids or other monomers into chains would be a vast water-based environment like the primordial soup or in the ocean near a hydrothermal vent. As the U.S. National Academy of Sciences notes, “Two amino acids do not spontaneously join in water. Rather, the opposite reaction is thermodynamically favored.” Similarly, origin of life theorists Stanley Miller and his intellectual heir Jeffrey Bada acknowledged that the polymerization of amino acids into peptides “is unfavourable in the presence of liquid water at all temperatures.” In other words, water breaks protein chains of monomers back down into amino acids (or other constituents), making it very difficult to produce longer peptides (or other polymers like RNA) in the primordial soup. Thus, the recent Nature article admits:
Chemists have not yet been able to synthesize such a wide range of biological molecules in conditions that mimic seawater.
The emerging evidence has caused many researchers to abandon the idea that life emerged in the oceans and instead focus on land environments, in places that were alternately wet and dry….
The open ocean is unviable, says Frenkel-Pinter, because there is no way for chemicals to become concentrated. “That’s really a problem,” agrees Bonfio.
A Way Around
The way around this, according to some, is to find a less-wet environment where primitive organic monomers can become concentrated in smaller pools of water, but then the water dries out, allowing “dehydration synthesis” of polymers to occur. Thus, the Nature article explains that another camp in origin of life research prefers the view that “the key molecules of life, and its core processes” formed in surface waters, such as “a relatively shallow body of water fed by streams.” This proposal does not go over well with the many origin of life theorists who prefer oceanic environments or undersea hydrothermal vents as the locality for where life arose:
The shift [from the ocean to the surface for the origin of life] is hardly unanimous, but scientists who support the idea of a terrestrial beginning say it offers a solution to a long-recognized paradox: that although water is essential for life, it is also destructive to life’s core components.
The article thus presents two catch-22’s for the origin of life:
the basic chemicals of life require ultraviolet radiation from sunlight to form, and that the watery environment had to become highly concentrated or even dry out completely at times
If it isn’t clear, the catch 22’s are as follows:
- UV radiation is required for certain vital building blocks to form, but too much UV radiation destroys those chemicals.
- Water is necessary for certain building blocks to form, but if the water isn’t removed then the next step in the origin of life can’t proceed so the monomers can form polymers.
As a partial solution, the article proposes that when you allow special cycles of “Intermittent drying” in the early steps required for the origin of life then more complex molecules can be formed. But this sounds like finely-tuned sets of events that are designed to create conditions “just right” for life to form. Indeed, the article even admits that such a solution requires “Goldilocks” conditions:
In other words, there might be a Goldilocks amount of water: not so much that biological molecules are destroyed too quickly, but not so little that nothing changes.
But there’s a much bigger problem — even if these lucky scenarios work: namely that producing these molecules is not tantamount to forming life:
Dry conditions, she says, provided an opportunity for chain molecules such as proteins and RNA to form.
But simply making RNA and other molecules is not life. A self-sustaining, dynamic system has to form.
To create such complex systems, however, you need chemical energy — which is the main attraction of hydrothermal vents, which are rich in chemical energy. However, for the reasons noted above, hydrothermal vents (and other aqueous environments) have their own problems. Nonetheless hydrothermal events still have their supporters:
An alternative marine idea has been championed since the 1980s by geologist Michael Russell, an independent researcher formerly at the Jet Propulsion Laboratory in Pasadena, California. Russell argues that life began in vents on the seabed, where warm alkaline water seeps up from geological formations below. Interactions between warm water and rocks would provide chemical energy that would first drive simple metabolic cycles, which would later start making and using chemicals such as RNA.
Russell is critical of Sutherland’s approach. “He’s doing all these fantastic bits of chemistry,” he says, but for Russell, none of it is relevant. That’s because modern organisms use completely different chemical processes to make substances such as RNA. He argues that these processes must have arisen first, not the substances themselves. “Life, it picks very particular molecules. But you can’t pick them from the bench. You’ve got to make them from scratch and that’s what life does.
Don’t miss the criticisms in the last paragraph: The problem with the surface-based model of the origin of life is that it’s just creating chemicals, but it can’t account for the biochemical pathways inherent to life. Of course there is then a counterpoint from surface-model advocates — namely that you can’t produce the chemicals you need for life under water:
“None of that synthesis exists in that deep-sea hydrothermal vent hypothesis. It just simply hasn’t been done, and possibly because it can’t be done,” says Catling.
Frenkel-Pinter is also critical of the vent idea, because the molecules she works with wouldn’t survive long in those conditions. “The formation of these protopeptides is not very compatible with hydrothermal vents,” says Frenkel-Pinter.
Again, we see a catch-22: at best you can either produce the chemicals you need for life or you can have access to chemical energy needed to drive biochemical reactions. But you can’t have both.
This is where origin of life researchers must get very creative — but the more creative they get, the more their solutions resemble teleology. One researcher proposed an ultra-Goldilocks solution, where an undersea hydrothermal vent somehow had “dry spaces” where the water could dry out. Not to be outdone, John Sutherland offered an even more complicated Goldilocks proposal where a meteorite hit the earth, and then…oh just read it for yourself:
a meteorite impact crater, heated by the Sun and by the residual energy of the impact, with multiple streams of water running down the sloping sides, and finally meeting in a pool at the bottom. This would have been a complex, 3D environment with mineral surfaces to act as catalysts, where carbon-based chemicals could have been alternately dissolved in water and dried out in the Sun.
One recalls James Tour’s analogy that compared state-of-the-art origin of life thinking to a story where an earthquake causes all of the ingredients for a cake to spill out of cupboards in just the right order so that a cake could be baked.
A Major Rift
In any case, the point is this: the Nature article acknowledges that the debate over the location of these early steps in the origin of life has led to a major rift in the field of origin of life research which requires more research to answer:
Where might all this have happened? On this point, there is a generational divide in the field. Many senior researchers are committed to one scenario or another, whereas younger researchers often argue that the question is wide open…
Narrowing down the location where life started will require understanding of the broader picture of prebiotic chemistry: how the many reactions fit together, and the ranges of conditions under which they occur.
So where does this leave us? For years we’ve been promised that the solution to the origin of life is just around the corner. Yet even today, in 2021, theorists cannot agree on basic questions about the location where the initial steps in the origin of life occurred. The reason for this is that each location has major downsides: An aqueous environment cannot concentrate molecules or form polymers and undersea hydrothermal vents tend to destroy prebiotic organic molecules. But on the surface of the earth there is no viable source of chemical energy to drive the chemical reactions needed for life, which forces researchers to appeal to Goldilocks scenarios where the amount of water, heat, and UV radiation must be “just right” so that the requisite molecules can form without being destroyed in the process.
Perhaps real progress will occur in future years. But for now, if anything is clear, it’s this: Origin of life theorists aren’t “coming very close” to explaining the origin of life, and the promises we’ve been given seem like empty bluffs, designed to keep people from straying off the precarious path that eventually leads, they hope, towards materialistic solutions.