Origin of Life Questions
Where did the first cell come from?
One of the biggest conundrums for those who assert that the diversity of life that we see arose strictly by naturalistic processes is the question of how the first living cell came into existence. The effort to find a naturalistic process has been complicated by the fact that the intricacies of the most simple of cells has made a naturalistic explanation virtually unthinkable. Take, for example, the following:
While many outside originoflife biology may still invoke "chance" as a causal explanation for the origin of biological information, few serious researchers still do. Since molecular biologists began to appreciate the sequence specificity of proteins and nucleic acids in the 1950s and 1960s, many calculations have been made to determine the probability of formulating functional proteins and nucleic acids at random. Even assuming extremely favorable prebiotic conditions and theoretically maximal reaction rates, such calculations have invariably shown that the probability of obtaining functionally sequenced biomacromolecules at random is, in Ilya Prigogines words, "vanishingly small . . . even on the scale of . . . billions of years." (Emphasis added.) Id., First Things Magazine, April 2000.
The latest and greatest hope for the evolution of life on Earth comes from heated underwater vents where it is theorized that the necessary chemicals may have come (miraculously) together to form a living cell.
The most detailed step-by-step blueprint for how Earth's oldest raw materials could have given rise to the stuff of life came out of the imagination of Gunter Wachtershauser, an organic chemist at the University of Regensberg in Germany. Ten years ago, Wachtershauser conceived of an assembly-line process at the ocean floor that transforms basic inorganic chemicals into organic chains, the biological molecules that are the building blocks of life.
Wachtershauser's factory enlists the elements of modern industry--all readily available at vents. The conveyor belt is the flat surface of metal sulfide minerals, such as iron pyrite, abundant in seafloor rocks. The raw materials are carbon- and hydrogen-rich gases from volcanic belches dissolved in the seawater. The workers that drive the assembly line--the keys to the whole process--are metallic ions in the sulfides.
In living cells, complex proteins called enzymes play the role of factory laborers, bringing certain molecules together and splitting others apart. Before enzymes appeared on the planet, Wachtershauser says that metallic ions filled that catalytic role. Without these mediators, reactions might take months or years, or never happen at all, he adds. New components would never get added to the molecules passing by on the conveyor.
In Wachtershauser's theory, the first organic molecule put together on the conveyor belt was acetic acid, a simple combination of carbon, hydrogen, and oxygen that is best known for giving vinegar its pungent odor. Formation of acetic acid is a primary step in metabolism, the series of chemical reactions that provides the energy that cells use to manufacture all the biological ingredients an organism needs.
According to the theory, metabolism came before all else. Once a primitive metabolism evolved, it began to run on its own, and only later were cells' other basic elements, such as a genetic code, invented.
Wachtershauser focuses on the heart of modern metabolism, the citric acid cycle. All living cells use this series of reactions to extract energy from food. The cycle makes changes in several chemical compounds, but it always begins with acetic acid. Inside a cell, the two carbon atoms in each acetic acid molecule are eventually expelled as carbon dioxide in a reaction that gives off a packet of energy.
Because the citric acid cycle is intrinsic to all modern life, Wachtershauser guesses that its basic reactions are close to the chemistry with which life began--with one significant variation. In the oxygen-deficient world at hydrothermal vents, heat-loving bacteria operate the cycle backward (SN: 3/29/97, p. 192). Instead of giving off carbon dioxide to make energy, they incorporate carbon atoms to build a succession of more complex organic molecules. Wachtershauser says life's first chemicals were built the same way.
Around the vents, he theorizes, catalytic metallic ions first enabled the materials around them to fashion acetic acid. In the next step, the ions catalyzed the addition of a carbon molecule to the acetic acid to get three-carbon pyruvic acid, which is another key chemical in the citric acid cycle and also reacts with ammonia to form amino acids, which themselves link up to form proteins.
From "Life's First Scalding Steps - hydrothermal vents may have been locus of origins of life - Abstract", Science News, Jan 9, 1999 by Sarah Simpson.
Well, there may be some problems with this theory that the subsurface vents could have been the breeding ground for the first cell. According to a new study catalogued by the National Academy of Science, the process would require the infusion of additional, specialized features for the cell to survive. As reported by Reasons to Believe:
In an attempt to give naturalistic origin-of-life scenarios as much time as possible, some scientists propose that life arose during the high temperature conditions of the Earths Hadean era, prior to 3.9 billion years ago. This scenario requires the first organisms to be heat-loving, thermophilic microbes. Results of a recent study make this scheme unlikely. Researchers demonstrate that in order to achieve chemical stability and functionality at high temperatures, specialized molecular features must be incorporated into the enzymes of thermophiles. This restriction reduces the probability that random processes can generate functional biomolecules at high temperatures. In other words, evolutionary scenarios for lifes origin are more difficult at high temperatures than at moderate temperatures in which this chemical restriction does not apply. The bottom line: origin-of-life researchers cannot look to the Hadean era for the time needed to make naturalistic origin-of-life scenarios plausible.
Develeena Mazumder et al., "Molecular Dynamic Studies of Ground State and Intermediate of the Hyperthermophilic Indole-3-Glycerol Phosphate Synthase," Proceedings of the National Academy of Sciences, USA 101 (2004): 14379-84.
Not having had the opportunity to see the study, I can't vouch for Reasons to Believe's characterization of the results. But if it is true, the latest (and possibly last) hope for a purely naturalistic process for the creation of the first single cell may have vanished.
For those of you who think that there is an obvious or known process by which the first single cells may have been formed, I have good news: you can become a millionaire! All you have to do is submit your solution to the "Origin of Life Prize." According to their website:
"The Origin-of-Life Prize" ® (hereafter called "the Prize") will be awarded for proposing a highly plausible mechanism for the spontaneous rise of genetic instructions in nature sufficient to give rise to life. To win, the explanation must be consistent with empirical biochemical, kinetic, and thermodynamic concepts as further delineated herein, and be published in a well-respected, peer-reviewed science journal(s).
Applicants must provide
A. a well-conceived, detailed hypothetical mechanism explaining how the rise of genetic instructions sufficient to give rise to life as defined in "Definitions" below might have occurred in Nature by natural processes, and an
B. empirical correlation to the real world of biochemistry and molecular biology - not just mathematical or computer models - of how the prescriptive information characteristic of all known living organisms might have arisen.
The mechanism must address four topics:
The simplest known genome's apparent anticipation and directing of future events toward biological ends, both metabolic and structural;
The ability of the genome to convey instructions, deliver orders, and actually produce the needed biological end-products;
The indirectness of recipe-like biological "linguistic" message code - the gap between genotypic prescriptive information (instruction) and phenotypic expression. How did the first genetic instruction arise in its coded format prior to phenotypic realization of progeny from which the environment could select? If a protobiont's genetic code and phenotype were one and the same, how did such a simple system self-organize to meet the nine minimum conditions of "life" enumerated below under "Definitions"? How did stellar energy, the four known forces of physics (strong and weak nuclear forces, electromagnetic force, and gravity), and natural processes produce initial prescriptive information (instruction/recipe) using direct or indirect code?
The bizarre concentration of singlehanded optical isomers (homochirality of enantiomers) in living things - how did a relatively pure population of left-handed amino acids or right-handed sugars arise out of a chemical environment wherein reactions ordinarily give rise to roughly equal numbers of both right- and left-handed optical isomers?
There you go. All it takes is the ability to research the answer to this perplexing problem and forward it to the Origin of Life Prize to recieve 20 years of payments of $50,000 each. Looking forward to that naturalistic explanation which I'm sure is forthcoming any day now . . . .