This experiment provided the structure for later research into the origin of life. Despite many revisions and additions, the Oparin-Haldane scenario remains part of the model in use today. The Miller-Urey experiment is simply a part of the experimental program produced by this paradigm. Wells says that the Miller-Urey experiment should not be taught because the experiment used an atmospheric composition that is now known to be incorrect.
Wells contends that textbooks don't discuss how the early atmosphere was probably different from the atmosphere hypothesized in the original experiment. Wells then claims that the actual atmosphere of the early earth makes the Miller-Urey type of chemical synthesis impossible, and asserts that the experiment does not work when an updated atmosphere is used.
Therefore, textbooks should either discuss the experiment as an historically interesting yet flawed exercise or not discuss it at all. Wells concludes by saying that textbooks should replace their discussions of the Miller-Urey experiment with an "extensive discussion" of all the problems facing research into the origin of life. These allegations might seem serious; however, Wells's knowledge of prebiotic chemistry is seriously flawed.
First, Wells's claim that researchers are ignoring the new atmospheric data, and that experiments like the Miller-Urey experiment fail when the atmospheric composition reflects current theories, is simply false.
The current literature shows that scientists working on the origin and early evolution of life are well aware of the current theories of the earth's early atmosphere and have found that the revisions have little effect on the results of various experiments in biochemical synthesis.
Despite Wells's claims to the contrary, new experiments since the Miller-Urey ones have achieved similar results using various corrected atmospheric compositions Figure 1 ; Rode, ; Hanic et al.
Further, although some authors have argued that electrical energy might not have efficiently produced organic molecules in the earth's early atmosphere, other energy sources such as cosmic radiation e.
Even if Wells had been correct about the Miller-Urey experiment, he does not explain that our theories about the origin of organic "building blocks" do not depend on that experiment alone Orgel, a. There are other sources for organic "building blocks," such as meteorites, comets, and hydrothermal vents. All of these alternate sources for organic materials and their synthesis are extensively discussed in the literature about the origin of life, a literature that Wells does not acknowledge.
In fact, what is most striking about Wells's extensive reference list is the literature that he has left out.
Wells apparently missed the vast body of literature on organic compounds in comets e. Kaplan et al. Wells also fails to cite the scientific literature on other terrestrial conditions under which organic compounds could have formed. These non-atmospheric sources include the synthesis of organic compounds in a reducing ocean e.
A cursory review of the literature finds more than 40 papers on terrestrial prebiotic chemical synthesis published since in the journal Origins of life and the evolution of the biosphere alone. Contrary to Wells's presentation, there appears to be no shortage of potential sources for organic "building blocks" on the early earth. Instead of discussing this literature, Wells raises a false "controversy" about the low amount of free oxygen in the early atmosphere.
Claiming that this precludes the spontaneous origin of life, he concludes that "[d]ogma had taken the place of empirical science" Wells In truth, nearly all researchers who work on the early atmosphere hold that oxygen was essentially absent during the period in which life originated Copley, and therefore oxygen could not have played a role in preventing chemical synthesis. This conclusion is based on many sources of data , not "dogma. Wells also neglects the data from paleosols ancient soils which, because they form at the atmosphere-ground interface, are an excellent source to determine atmospheric composition Holland, Reduced paleosols suggest that oxygen levels were very low before 2.
There are also data from mantle chemistry that suggest that oxygen was essentially absent from the earliest atmosphere Kump et al. Current data show that oxygen levels did not start to rise significantly until nearly 1. Wells strategically fails to clarify what he means by "early" when he discusses the amount of oxygen in the "early" atmosphere.
In his discussion he cites research about the chemistry of the atmosphere without distinguishing whether the authors are referring to times before, during, or after the period when life is thought to have originated. Nearly all of the papers he cites deal with oxygen levels after 3.
They are irrelevant, as chemical data suggest that life arose 3. Finally, the Miller-Urey experiment tells us nothing about the other stages in the origin of life, including the formation of a simple genetic code PNA or "peptide"-based codes and RNA-based codes or the origin of cellular membranes liposomes , some of which are discussed in all the textbooks that Wells reviewed.
The Miller-Urey experiment only showed one possible route by which the basic components necessary for the origin of life could have been created, not how life came to be. You just studied 15 terms! Miller and Urey concluded that the basis of spontaneous organic compound synthesis or early earth was due to the primarily reducing atmosphere that existed then.
A reducing environment would tend to donate electrons to the atmosphere, leading to reactions that form more complex molecules from simpler ones. They found that several organic amino acids had formed spontaneously from inorganic raw materials. C The presence of a constant electrical charge is a potential limitation of the Miller-Urey apparatus, because it causes experimental conditions to differ from the conditions scientists believe actually existed in the primitive atmosphere.
The problem recognised by Miller and his colleagues was that oxygen would destroy any organic material in the experiment and certainly in the period of time they allocated to the early period on the planet. For example, when we die, we decay.
Which is the strongest criticism of the Miller-Urey experiment? It relied on hypotheses about what conditions were like on early Earth that may not be accurate. The electrodes were used to spark the fire to imitate lightning and storm through water vapour.
In the first portion of section Because of this many experiments have since been done, showing that the molecules of life can form in a wide variety of environments with different starting chemicals and different sources of energy. Sugars, lipids and amino acids have even been found on meteorites, this suggests that the molecules of life formed all throughout the ancient solar system, and may be forming right now in other regions of our galaxy!
The Miller-Urey experiment is significant for two main reasons: First, though it was not a perfect simulation of the early Earth, it clearly demonstrated, for the first time, that biomolecules can form under ancient Earth-like conditions. Second, the experiment took what was once mere speculation, the idea that life may have emerged from chemistry and transformed a portion of that speculation into legitimate, testable science!
The theory of evolution tells us how life diversified after it got started, but how did the first evolving creatures come about? Playback 7 minutes. Related Videos. Georgia Chemistry 3 Chemical composition in compounds and chemical reactions.
Georgia Chemistry 4 Engineering principles to manipulate the factors that affect a chemical reaction. Georgia Chemistry 6 The nature of acids and bases. Conover, PhD Eric T. Parker, PhD Nicholas V. Hud, PhD Tom Cochran. So to sum things up, what was the Miller-Urey experiment?
The effect of the buffer in the selectivity of the reactions and possible reaction pathways for the formation of compounds 1 — 48 are discussed in Supplementary text SI 5. Our results demonstrate that the wall of the reactors plays a crucial role in the synthesis of organic compounds in the Miller-Urey experiment. As summarized in Fig. Furthermore, few hours after sparking, the wall of the borosilicate flask is covered by a thin brown film of organic matter.
Noticeably, this film only forms on the part of the wall above the water level of the reactor. The color of the solution in the borosilicate reactors is yellow—brown and is full of brown organic particles visible to the naked eye.
In none of the Teflon reactors, the formation of this organic film was observed. The silanol groups on the surface of the glass, and traces of metal that could be released by dissolution under the alkaline conditions of the experiment may contribute to the observed reactivity 27 , The presence of Si—O—H groups enhanced by the alkaline conditions facilitates the absorption of the organic molecules synthesized in the gas and the liquid water in contact with the glass This could explain the formation of the brown film covering the inner surface of the borosilicate flask.
The film appears as a translucent orange matrix under the optical microscope Fig. The infrared and Raman spectra of the freshly formed film Fig. It also shows that it works as a matrix embedding and concentrating organic molecules, including urea 3 , glycine 5 , lactic acid 28 , adenine 36 , cytosine 39 , guanidine 49 , succinic acid 50 , 2,4-diaminohydroxypyrimidine 51 , hypoxanthine 52 , and four polycyclic aromatic hydrocarbons, namely anthracene 53, chrysene 54 , pyrene 55 , and dibenz a,h anthracene 56 Fig.
Among them, 49 — 56 were not previously detected in the liquid fraction of the experiment. As a general trend, the total yield of these latter compounds was found to increase after acid hydrolysis 31 , highlighting the possibility that the treatment favored their extraction from the solid matrix See supplementary information Table S5 condition A vs.
The EDX analysis of the film reveals the existence of a significant amount of silica Fig. The formation of organosilicon compounds is most likely responsible for the incomplete mass balance relative to the crude Table 1.
In addition, the highest total yield for the reaction products observed under unbuffered conditions is in accordance with a possible role of borosilicate as a catalyst for prebiotic processes Table 1 , entry 7. From the initial bet of Bernal and Goldsmichdt for montmorillonite 32 , many other minerals have been proposed to speed up the synthesis of specific molecules required for life as we know it, namely other clays, zeolites, sulfides, iron oxide, layered hydroxides, silica, etc.
Experimental and theoretical work has been published to support these claims In particular, simple variations in environmental mineral composition lead to differentiation of distinct chemical pathways 36 , encompassing the role of mineral surface in the prebiotic origin of amino acids 37 and peptides 38 , mechanochemical solid-state transformations 39 , and borosilicate-mediated formose condensation in the synthesis and stabilization of biologically relevant four and six-carbon sugars However, we still miss a good understanding of the structural reasons why and how mineral surfaces catalyze reactions relevant to prebiotic chemistry and the origin of life The importance of our results lies in the fact that, for the first time, the role of borosilicate has been experimentally demonstrated in a type of synthesis of the utmost relevance for the inorganic generation of organic compounds from scratch.
The famous Miller-Urey synthesis triggered by sparking would be highly efficient at any place of the universe, provided a mineral surface is available. Noteworthy, silica and silicates also trigger the formation of insoluble organic matrices that serve as niches for the preservation and concentration of forming prebiotic molecules. These abiotic organic films may have formed in Earth-like planets and moons as Mars and several moons of the solar system 41 , 42 , For instance, a large fraction of the organic matter found in Archean rocks and to be found in the robotic exploration of Mars might reasonably be of inorganic origin.
The putative role of the organic film triggered by the borosilicate reactors as a milieu for absorption and concentration of organic molecules should be further investigated. And indeed, the formation and properties of these organic films must be explored with different mineral surfaces and different atmospheres. The experiment is especially important in the framework of the new ideas about the Hadean Earth in which the concomitance of a reduced atmosphere, electrical storms, silicate-rich rocky surfaces, and liquid water is expected 31 , The presence of high molecular weight products is exemplified by the presence of a dipeptide, of multi-carbon atoms dicarboxylic acids, of PAHs 47 , of a complete panel of biological nucleobases, and, markedly, by the rich variety of different classes of compounds.
In summary, Miller recreated in his experiments the atmosphere and waters of the primitive Earth. The role of the rocks was hidden in the walls of the reactors. The electric discharge was performed under unbuffered and buffered solution NH 4 Cl, 0. After the work-up, the reaction was lyophilized and immediately analyzed by GC—MS. GC—MS fragmentation spectra were recovered by using a triple quadrupole MS analyzer as full scan and single ion research modes, and compared with commercially available electron mass spectrum libraries.
These libraries also include isomeric structures. They tentatively identify unknown structure on the basis of the crossing of multiple experimental parameter values i. All products have been recognized with a similarity index S. The yield of reaction products was calculated in triplicate as micrograms of product per 1. Miller, S. A production of amino acids under possible primitive earth conditions.
Science , — Ball, P. Google Scholar. Production of some organic compounds under possible primitive earth conditions1. Synthesis of organic compounds by electric discharges. Nature , — Schlesinger, G. Miyakawa, S. Prebiotic synthesis from CO atmospheres: Implications for the origins of life. PNAS 99 , — Cooper, G. Miller-Urey spark-discharge experiments in the deuterium world. Wollrab, E. Life Evol. Johnson, A. The Miller volcanic spark discharge experiment. Parker, E. Primordial synthesis of amines and amino acids in a Miller H2S-rich spark discharge experiment.
PNAS , — Garcia-Ruiz, J. Self-assembled silica-carbonate structures and detection of ancient microfossils.
0コメント