Can naturalism account for the origin of the 20 amino acids in living systems?

Do the Miller-Urey experiments simulate the early Earth?
Do the Miller-Urey experiments simulate the early Earth?

The origin of life

There are two problems related to the origin of the first living cell, on naturalism:

  1. The problem of getting the building blocks needed to create life – i.e. the amino acids
  2. The problem of creating the functional sequences of amino acids and proteins that can support the minimal operations of a simple living cell

Normally, I concede the first problem and grant the naturalist all the building blocks he needs. This is because step 2 is impossible. There is no way, on naturalism, to form the sequences of amino acids that will fold up into proteins, and then to form the sequences of proteins that can be used to form everything else in the cell, including the DNA itself. But that’s a topic for a separate post.

Today, let’s take a look at the problems with step 1.

The problem of getting the building blocks of life

Now you may have heard that some scientists managed to spark some gasses to generate most of the 20 amino acids found in living systems. These experiments are called the “Miller-Urey” experiments.

The IDEA center has a nice summary of origin-of-life research that explains a few of the main problems with step 1.

Miler and Urey used the wrong gasses:

Miller’s experiment requires a reducing methane and ammonia atmosphere,11, 12 however geochemical evidence says the atmosphere was hydrogen, water, and carbon dioxide (non-reducing).15, 16 The only amino acid produced in a such an atmosphere is glycine (and only when the hydrogen content is unreasonably high), and could not form the necessary building blocks of life.11

Miller and Urey didn’t account for UV of molecular instability:

Not only would UV radiation destroy any molecules that were made, but their own short lifespans would also greatly limit their numbers. For example, at 100ºC (boiling point of water), the half lives of the nucleic acids Adenine and Guanine are 1 year, uracil is 12 years, and cytozine is 19 days20 (nucleic acids and other important proteins such as chlorophyll and hemoglobin have never been synthesized in origin-of-life type experiments19).

Miller and Urey didn’t account for molecular oxygen:

We all have know ozone in the upper atmosphere protects life from harmful UV radiation. However, ozone is composed of oxygen which is the very gas that Stanley Miller-type experiments avoided, for it prevents the synthesis of organic molecules like the ones obtained from the experiments! Pre-biotic synthesis is in a “damned if you do, damned if you don’t” scenario. The chemistry does not work if there is oxygen because the atmosphere would be non-reducing, but if there is no UV-light-blocking oxygen (i.e. ozone – O3) in the atmosphere, the amino acids would be quickly destroyed by extremely high amounts of UV light (which would have been 100 times stronger than today on the early earth).20, 21, 22 This radiation could destroy methane within a few tens of years,23 and atmospheric ammonia within 30,000 years.15

And there were three other problems too:

At best the processes would likely create a dilute “thin soup,”24 destroyed by meteorite impacts every 10 million years.20, 25 This severely limits the time available to create pre-biotic chemicals and allow for the OOL.

Chemically speaking, life uses only “left-handed” (“L”) amino acids and “right-handed” (“R)” genetic molecules. This is called “chirality,” and any account of the origin of life must somehow explain the origin of chirality. Nearly all chemical reactions produce “racemic” mixtures–mixtures with products that are 50% L and 50% R.

Two more problems are not mentioned in the article. A non-peptide bond anywhere in the chain will ruin the chain. You need around 200 amino acids to make a protein. If any of the bonds is not a peptide bond, the chain will not work in a living system. Additionally, the article does not mention the need for the experimenter to intervene in order to prevent interfering cross-reactions that would prevent the amino acids from forming.

Usually when you hear the origin of life debated, they sort of skirt about the problem of where the amino acids come from, but there is no reason not to make that an issue. The naturalist has to explain how the first living cell could come about naturalistically.

Positive arguments for Christian theism


6 thoughts on “Can naturalism account for the origin of the 20 amino acids in living systems?”

  1. Even had Miller-Urey succeeded, would this not be a case for intelligent design, since Miller and Urey are presumably intelligent?

  2. As a chemist, I am not willing to give anyone a pass on the chirality. All amino acids except for glycine are chiral. A single wrong stereocenter can completely change a molecule. Consider that most of your protein strand is made a chiral amino adds, and then consider what anyone who has done any organic synthesis would think of your odds.

  3. I deleted a bunch of off-topic comments by someone who wanted to talk about philosophy instead of science. Would love to see a naturalistic explanation for the evidence described in the post. This is a blog post about science, not philosophy.

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