There they go again: telling us baloney about the origin of life. Among the phony or only half-true headlines written this week by our science journalists were these :
- "Key building block for life discovered on distant asteroid Ryugu — and it could explain how life on Earth began" (LiveScience.com)
- "Asteroid discovery suggests ingredients for life on Earth came from space" (Yahoo News)
- "Asteroid discovery suggests life on Earth came from space billions of years ago." (Fox News)
These headlines refer to a claimed discovery of a negligible amount of a chemical called uracil in soil retrieved from the asteroid Ryugu. None of the three stories above mention the amount of uracil that was reported. The amount reported in the scientific paper was about 13 parts per billion. The paper states: "the concentration of uracil before acid hydrolysis is estimated to be 7 ± 4 and 21 ± 6 ppb in the A0106 and C0107 samples, respectively." Unfortunately, when something is reported in concentrations so low, you can't have very much confidence in the reliability of the result.
For example, in 2020 some scientists reported they detected phosphine in the atmosphere of Venus, at a level of 20 parts per billion. But other scientists who analyzed the same data said that it provided no clear evidence of phosphine. It seems that claims of finding things at barest trace levels such as 20 parts per billion are not very reliable. Moreover, there is a chance of terrestrial contamination, which is what would have happened if a tiny trace of the Earth's uracil (found in all living things) managed to contaminate the soil sample from the asteroid Ryugu.
Even if the reported amount of uracil is correct (a very big "if"), an amount so negligible would do nothing to "explain how life on Earth began," and does not at all suggest "life on Earth came from space" or that "ingredients for life on Earth came from space." Making such claims are sillier than claiming that moon dust can feed astronauts after finding that moondust has 20 parts per billion of sugar. We can imagine some manufacturing process that might extract such microscopic traces of sugar if they existed in moon dust, but we can imagine no natural process that would extract uracil from some asteroid dust that was 99.99999999% biologically irrelevant stuff.
One problem in explaining the origin of life is the difficulty of explaining the origin of all the necessary building blocks. The table below shows the various types of the lowest building blocks of life. As indicated below, there are reasons for doubting that the amino acids, ribose sugars, purines, and nucleotides would have existed in sufficient quantity for DNA, RNA and proteins to originate.
| Components |
| RNA, DNA | Ribose sugars.
| Harvard science web site: "In experiments ribose could not be made at the necessary quantities that would explain its abundance on early Earth because it was highly unstable."
A scientific paper says this:
"Sugars are known to be unstable in strong acid or base, but there are few data for neutral solutions. Therefore, we have measured the rate of decomposition of ribose between pH 4 and pH 8 from 40 degrees C to 120 degrees C. The ribose half-lives are very short (73 min at pH 7.0 and 100 degrees C and 44 years at pH 7.0 and 0 degrees C)... These results suggest that the backbone of the first genetic material could not have contained ribose or other sugars because of their instability.”
A NASA press release notes "sugars and nucleobases (components of DNA and RNA)...have not yet been identified in samples returned from Ryugu,” referring to samples returned from an asteroid, by a Japanese space mission. Ribose sugar was reported in three meteorites, with abundances between 4 and 25 parts per billion. Terrestrial contamination is a possible source of such reports. | | Phosphates | A simple chemical with one phosphate atom and four oxygen atoms. Types of phosphates may have been detected in a subsurface ocean of Enceladus, a moon of Saturn.
| Pyrimidines (type of nitrogenous base): cytosine, thymine, and uracil
| A 2023 paper reports uracil in parts of only about 12 parts per billion in a sample returned from an asteroid. Cytosine and thymine have not been detected in samples returned from an asteroid. | Purines (type of nitrogenous base): adenine and guanine.
| More complex than pyrimidines. According to this paper, it is hard to explain an abiotic origin, in a way compatible with formation of ribose sugars. A paper says that "gas-phase adenine and uracil will be destroyed within hours in the Earth's vicinity," because of sensitivity to ultraviolet radiation. No adenine or guanine was found in samples returned from the asteroid Ryugu. | | Nucleosides (combination of ribose sugar and pyrimidines or purines) and nucleotides (a nucleoside plus a phosphate) | Wikipedia article: “No known chemical pathways for the abiogenic synthesis of nucleotides from pyrimidine nucleobases cytosine and uracil under prebiotic conditions." Nucleosides have not been found in space. |
|
| Proteins | Amino Acids. The twenty amino acids used by living things are: Alanine, Asparagine, Aspartic acid, Arginine, Cysteine, Glutamine,
Glycine, Glutamic acid, Histidine,
Isoleucine,
Lysine,Leucine, Phenylalanine, Methionine, Serine, Proline,
Tryptophan,Threonine, Tyrosine, and Valine.
| None of the amino acids used by living things have ever been produced in any experiment realistically simulating early Earth conditions. The famous Miller-Urey experiment was not any such thing. As discussed at length here, the Miller-Urey experiment failed in multiple ways to realistically simulate early Earth conditions, with the failures including (1) use of an enclosed glass apparatus that would not have been available; (2) excessive bombardment of electricity (continuous bombardment every other day), unlike anything that would have occurred in the early Earth; (3) an incorrect mixture of gases not matching the atmosphere of the early Earth.
The only claims of detecting an amino acid on another planet or moon is a dubious claim of detecting the simplest amino acid (glycine) in a very tiny trace amount (1 part in a billion) in the atmosphere of Venus. Made by one paper, the claim has not been replicated by another paper. Since a claim recently of phosphine in the atmosphere of Venus in the trace amount of 20 parts per billion was disputed by several other scientific papers (here, here and here), we can have little confidence in the claim of a much smaller 1 part per billion abundance of glycine in the atmosphere of Venus. No amino acids or sugars have been found on Mars or on Saturn's large moon Titan (where about 20 other chemicals have been detected) or an Enceladus (another large moon of Saturn where some chemicals have been detected, but not amino acids or sugars). A claim has been made that some amino acids existed in a meteorite (Nakhla) reputed to have come from Mars, but the paper making that claim says, "The amino acids in Nakhla appear to be derived from terrestrial organic matter that infiltrated the meteorite soon after its fall to Earth."
The Stardust mission returning a dust sample from a comet found only one of the twenty amino acids used by living things: glycine, the simplest of these amino acids. The abundance was only about 1 part per billion.
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The table below clarifies the relation between the complexity of these chemicals and whether or not they have been found in space. The relation is a simple one. None of these chemicals with a molecular weight greater than about 112 has been found in space.
|
Chemical
|
Type
|
Molecular weight
|
Found in space?
|
|
Glycine
|
Amino acid
|
57
|
Yes
|
|
Alanine
|
Amino acid
|
71
|
Yes (?)
|
|
Serine
|
Amino acid
|
87
|
No
|
|
Proline
|
Amino acid
|
97
|
No
|
|
Valine
|
Amino acid
|
99
|
Yes (?)
|
|
Threonine
|
Amino acid
|
101
|
No
|
|
Cysteine
|
Amino acid
|
103
|
No
|
|
Cytosine
|
Pyrimidine
|
111
|
No
|
|
Uracil
|
Pyrimidine
|
112
|
Yes (?)
|
|
Isoleucine
|
Amino acid
|
113
|
No
|
|
Leucine
|
Amino acid
|
113
|
No
|
|
Asparagine
|
Amino acid
|
114
|
No
|
|
Aspartic
acid
|
Amino acid
|
115
|
No
|
|
Glutamine
|
Amino acid
|
128
|
No
|
|
Thymine
|
Pyrimidine
|
126
|
No
|
|
Adenine
|
Purine
|
135
|
No
|
|
Guanine
|
Purine
|
151
|
No
|
|
Lysine
|
Amino acid
|
128
|
No
|
|
Glutamic
acid
|
Amino acid
|
129
|
No
|
|
Methionine
|
Amino acid
|
131
|
No
|
|
Histidine
|
Amino acid
|
137
|
No
|
|
Phenylalanine
|
Amino acid
|
147
|
No
|
|
Arginine
|
Amino acid
|
156
|
No
|
|
Arginine
|
Amino acid
|
156
|
No
|
|
Tyrosine
|
Amino acid
|
163
|
No
|
|
Tryptophan
|
Amino acid
|
186
|
No
|
Below is a good analogy for the people trying to take comfort in the discovery in space of the tiniest trace amounts of a few of the lowest building blocks of life. Let us imagine a person who gets the extremely ridiculous idea that well-written books can arise from chance arrangements of falling leaves. The person might examine natural piles of falling leaves, looking for something that looks like letters of the English alphabet. He would no doubt be able to find a few very rare examples of something in a natural leaf pile resembling a letter of the alphabet. But it would be extremely absurd for the person to announce that finding a few such cases would do anything to substantiate the idea that falling leaves can write well-written books. It would be very ridiculous for the person to make a statement like the one below:
This is a fair analogy regarding abiogenesis claims (claims that life can arise from mere lifeless chemicals), for three reasons:(1) The information complexity of even the simplest living thing is comparable to the information complexity of a book. Trying to strip down the simplest living cells so that they are left with the simplest self-reproducing cell, scientists are left with a cell still requiring hundreds of proteins, most of which require hundreds of well-arranged amino acids. Just as even the simplest adult book (having only about 30 pages) requires about 30,000 well-arranged characters or letters, the simplest one-celled living thing requires about 30,000 well-arranged amino acids.
(2) Just as there are 26 letters in the English alphabet, each with a different appearance, there are 20 amino acids used by living things, each with a different structure.
(3) Just as within piles of leaves the vast majority of material consists of that which does not look like any building block of a book (a letter of the alphabet), the matter in asteroids and comets is 99.9999999% chemical material that is not any of the lowest building blocks of life. Just as there would be no way for natural processes to extract rare parts of leaf piles that looked like letters, and make such rare parts into books, there would be no way for natural processes to extract trace parts of asteroids or comets that consisted of any of the building blocks of life listed above, and to make a living thing from only those extracted parts.
So the chance of chemicals accidentally forming into a self-reproducing cell is roughly comparable to the chance of falling leaves producing a well-written book of about 30 pages. Just as we would never expect any pile of leaves to result in a well-written book (even if there were a billion trillion quadrillion trees in the universe), we would never expect the accidental appearance of life from random chemical combinations to ever occur even if there were a billion trillion planets scattered across 100 billion galaxies. Extraterrestrial life could still be abundant in the univere, but only if there is some purposeful agency causing such abundance.
In scientific papers we can find many confessions that totally conflict with common achievement boasts of biologists. For example, a 2022 paper ("Toward a theory of evolution as multilevel learning") makes this little confession: "Modern evolutionary theory gives a detailed quantitative description of microevolutionary processes that occur within evolving populations of organisms, but evolutionary transitions and emergence of multiple levels of complexity remain poorly understood." Which is another way of saying biologists do not actually understand how our planet got organisms such as birds, bears and humans. In the same paper we read this:
"Modern evolutionary theory, steeped in population genetics gives a detailed and arguably, largely satisfactory account of
microevolutionary processes: that is, evolution of allele frequencies in a population of organisms under selection and random genetic drift. However, this theory has little to say
about the actual history of life, especially the emergence of new
levels of biological complexity, and nothing at all about the origin of life."
So why on Earth have he heard a hundred and one evolutionary biologists speaking as if evolutionary theory was some explanation of biological complexity? It sounds like our evolutionary biologists jumped the gun and crowned themselves as grand Lords of Explanation, pinning on their chests self-devised merit badges boasting of things never actually done.
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