state oparin and haldane hypothesis

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AP®︎/College Biology

Course: ap®︎/college biology   >   unit 7.

• Earth formation
• Beginnings of life
• Origins of life

Hypotheses about the origins of life

• The RNA origin of life
• Origins of life on Earth

Key points:

• The Earth formed roughly 4.5 ‍   billion years ago, and life probably began between 3.5 ‍   and 3.9 ‍   billion years ago.
• The Oparin-Haldane hypothesis suggests that life arose gradually from inorganic molecules, with “building blocks” like amino acids forming first and then combining to make complex polymers.
• The Miller-Urey experiment provided the first evidence that organic molecules needed for life could be formed from inorganic components.
• Some scientists support the RNA world hypothesis , which suggests that the first life was self-replicating RNA. Others favor the metabolism-first hypothesis , placing metabolic networks before DNA or RNA.
• Simple organic compounds might have come to early Earth on meteorites.

Introduction

When did life appear on earth, the earliest fossil evidence of life, how might life have arisen.

• Simple inorganic molecules could have reacted (with energy from lightning or the sun) to form building blocks like amino acids and nucleotides, which could have accumulated in the oceans, making a "primordial soup." 3 ‍  
• The building blocks could have combined in further reactions, forming larger, more complex molecules (polymers) like proteins and nucleic acids, perhaps in pools at the water's edge.
• The polymers could have assembled into units or structures that were capable of sustaining and replicating themselves. Oparin thought these might have been “colonies” of proteins clustered together to carry out metabolism, while Haldane suggested that macromolecules became enclosed in membranes to make cell-like structures 4 , 5 ‍   .

From inorganic compounds to building blocks

Were miller and urey's results meaningful, from building blocks to polymers, what was the nature of the earliest life, the "genes-first" hypothesis, the "metabolism-first" hypothesis, what might early cells have looked like, another possibility: organic molecules from outer space.

• Miller, Urey, and others showed that simple inorganic molecules could combine to form the organic building blocks required for life as we know it.
• Once formed, these building blocks could have come together to form polymers such as proteins or RNA.
• Many scientists favor the RNA world hypothesis, in which RNA, not DNA, was the first genetic molecule of life on Earth. Other ideas include the pre-RNA world hypothesis and the metabolism-first hypothesis.
• Organic compounds could have been delivered to early Earth by meteorites and other celestial objects.

Works cited:

• Harwood, R. (2012). Patterns in palaeontology: The first 3 billion years of evolution. Palaeontology , 2(11), 1-22. Retrieved from http://www.palaeontologyonline.com/articles/2012/patterns-in-palaeontology-the-first-3-billion-years-of-evolution/ .
• Wacey, D., Kilburn, M. R., Saunders, M., Cliff, J., and Brasier, M. D. (2011). Microfossils of sulphur-metabolizing cells in 3.4-billion-year-old rocks of Western Australia. Nature Geoscience , 4 , 698-702. http://dx.doi.org/10.1038/ngeo1238 .
• Primordial soup. (2016, January 20). Retrieved May 22, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Primordial_soup .
• Gordon-Smith, C. (2003). The Oparin-Haldane hypothesis. In Origin of life: Twentieth century landmarks . Retrieved from http://www.simsoup.info/Origin_Landmarks_Oparin_Haldane.html .
• The Oparin-Haldane hypothesis. (2015, June 14). In Structural biochemistry . Retrieved May 22, 2016 from Wikibooks: https://en.wikibooks.org/wiki/Structural_Biochemistry/The_Oparin-Haldane_Hypothesis .
• Kimball, J. W. (2015, May 17). Miller's experiment. In Kimball's biology pages . Retrieved from http://www.biology-pages.info/A/AbioticSynthesis.html#Miller's_Experiment .
• Earth’s early atmosphere. (Dec 2, 2011). In Astrobiology Magazine . Retrieved from http://www.astrobio.net/topic/solar-system/earth/geology/earths-early-atmosphere/ .
• McCollom, T. M. (2013). Miller-Urey and beyond: What have learned about prebiotic organic synthesis reactions in the past 60 years? Annual Review of Earth and Planetary Sciences , 41_, 207-229. http://dx.doi.org/10.1146/annurev-earth-040610-133457 .
• Powner, M. W., Gerland, B., and Sutherland, J. D. (2009). Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions. Nature , 459 , 239-242. http://dx.doi.org/10.1038/nature08013 .
• Lurquin, P. F. (June 5, 2003). Proteins and metabolism first: The iron-sulfur world. In The origins of life and the universe (pp. 110-111). New York, NY: Columbia University Press.
• Ferris, J. P. (2006). Montmorillonite-catalysed formation of RNA oligomers: The possible role of catalysis in the origins of life. Philos. Trans. R. Soc. Lond. B. Bio.l Sci ., 361 (1474), 1777–1786. http://dx.doi.org/10.1098/rstb.2006.1903 .
• Kimball, J. W. (2015, May 17). Assembling polymers. In Kimball's biology pages . Retrieved from
• Montmorillonite. (2016, 28 March). Retrieved May 22, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Montmorillonite .
• Wilkin, D. and Akre, B. (2016, March 23). First organic molecules - Advanced. In CK-12 biology advanced concepts . Retrieved from http://www.ck12.org/book/CK-12-Biology-Advanced-Concepts/section/10.8/ .
• Hollenstein, M. (2015). DNA catalysis: The chemical repertoire of DNAzymes. Molecules , 20 (11), 20777–20804. http://dx.doi.org/10.3390/molecules201119730 .
• Breaker, R. R. and Joyce, G. F. (2014). The expanding view of RNA and DNA function. Chemistry & biology , 21 (9), 1059–1065. http://dx.doi.org/10.1016/j.chembiol.2014.07.008 .
• Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., and Walter, P. (2002). A pre-RNA world probably predates the RNA world. In Molecular biology of the cell (4th ed.). New York, NY: Garland Science. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK26876/#_A1124_ .
• Moran, L. A. (2009, May 15). Metabolism first and the origin of life. In Sandwalk: Strolling with a skeptical biochemist . Retrieved from http://www.simsoup.info/Origin_Landmarks_Oparin_Haldane.html .
• Kimball, J. W. (2015, May 17). The first cell? In Kimball's biology pages . Retrieved from http://www.biology-pages.info/A/AbioticSynthesis.html#TheFirstCell?
• Kimball, J. W. (2015, May 17). Molecules from outer space? In Kimball's biology pages . Retrieved from http://www.biology-pages.info/A/AbioticSynthesis.html#Molecules_from_outer_space? .
• Jeffs, W. (2006, November 30). NASA scientists find primordial organic matter in meteorite. In NASA news . Retrieved from http://www.nasa.gov/centers/johnson/news/releases/2006/J06-103.html .

Additional references:

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Structural Biochemistry/The Oparin-Haldane Hypothesis

The Oparin-Haldane Hypothesis

The Oparin-Haldane hypothesis is a hypothesis independently developed by two scientists: Russian chemist A.I. Oparin and British scientist John Haldane.

Both independently suggested that if the primitive atmosphere was reducing (as opposed to oxygen-rich), and if there was an appropriate supply of energy, such as lightning or ultraviolet light, high temp of around 1073 K then a wide range of organic compounds might be synthesized.

Oparin came up with the hypothesis in 1924 that Earth’s atmosphere was extremely reducing in its early stages of development. This means that the atmosphere had an excess of negative charge and could cause reducing reactions by adding electrons to compounds. Oparin suggested that these organic compounds could have undergone a series of reactions leading to more and more complex molecules. Under these circumstances, Oparin hypothesized that organic molecules could have formed from simple inorganic molecules.He proposed that the molecules formed colloid aggregates, or 'coacervates', in an aqueous environment. These coacervates were able to absorb and assimilate organic compounds from the environment in a way reminiscent of metabolism. They would have taken part in evolutionary processes, eventually leading to the first lifeforms.

Similarly, in 1929, before Haldane read about Oparin’s theory of a reducing atmosphere, Haldane also hypothesized that the early stages of Earth’s atmosphere was reducing, which could catalyze reactions that would form more complicated organic molecules from simpler molecules. Haldane hypothesized that the oceans served as a huge cooking pot where powered by the sun or lightning, chemical reactions could occur in an aqueous environment to form a huge diversity of organic compounds. Haldane proposed that the primordial sea served as a vast chemical laboratory powered by solar energy. The atmosphere was oxygen free, and the combination of carbon dioxide, ammonia and ultraviolet radiation gave rise to a host of organic compounds. The sea became a 'hot dilute soup' containing large populations of organic monomers and polymers. Haldane envisaged that groups of monomers and polymers acquired lipid membranes, and that further developments eventually led to the first living cells.

Haldane coined the term 'prebiotic soup' or 'prebiotic atmosphere' that consisted of an abundance of methane, ammonia, and water. This term became a powerful symbol of the Oparin-Haldane view of the origin of life.

Miller-Urey Experiment

In 1953, two scientists set out to test Oparin and Haldane's hypothesis. Harold Urey and his student Stanley Miller tried to calculate the chemical constituents of the atmosphere of the early Earth. They based their calculations on the view that the early atmosphere was reducing. In order to do this, they simulated early earth atmospheric conditions by creating a closed system which contained water, methane gas, ammonia, and hydrogen gas in 2:1:2 ratio along with water vapours and along with it kept a high temperature of 1073 K.Urey suggested that his student, Miller should attempt to synthesize organic compounds in this type of atmosphere.

Miller carried out an experiment in which he passed a continuous spark discharge at 75,000 volts through a flask containing the gases identified by Urey along with water. Furthermore, this electrical current was run through the laboratory set up to simulate the catalytic source of lightning that was present in the early atmosphere.

Miller found that after 18 days of circulating the mixture, most of the ammonia and much of the methane had been consumed. The main gaseous products were carbon monoxide (CO) and nitrogen (N 2 ). In addition, there was an accumulation of dark material in the water. Few of the specific constituents of this could not be identified, but it was clear that the material included a large range of organic polymers. From the results of their experiment, they found that up to 15% of the carbon in the system was inorganic compounds that had formed in the system. This conclusion proved that organic molecules could be formed from inorganic molecules in Earth’s early atmosphere. In addition, out of the organic molecules produced, Miller and Urey showed that some of the organic compounds were amino acids, which are necessary for living organisms.

Analysis of the aqueous solution showed that the following had also been synthesized:

1. 25 amino acids (the main ones being glycine, alanine and aspartic acid)

2. Several fatty acids

3. Hydroxy acids

4. Amide products.

Aftermath of the Miller-Urey Experiment

The Miller-Urey experiment was immediately recognized as an important breakthrough in the study of the origin of life. It was received as confirmation of the Oparin-Haldane hypothesis in that several of the key molecules of life could have been synthesised on the primitive Earth in the kind of conditions envisioned by Oparin and Haldane. These molecules would then have been able to take part in prebiotic chemical processes, leading to the origin of life.

Other similar experiments have been done to mimic early Earth conditions in an attempt to find other ways organic molecules could have formed. One experiment was done to mimic deep underwater volcano conditions. At these underwater volcanoes, catalytic heat as well as many minerals were constantly supplied. This provided an ideal system for organic molecules to be formed. This system was also found to produce amino acids, which is essential for living organisms to process into proteins.

Since the Miller-Urey experiment, a great deal of effort has been spent investigating prebiotic chemistry. It has become apparent that organizing simple molecules into assemblies capable of reproducing and evolving is a far greater task than was generally realized during the excitement that followed the experiment. In addition, the view that the early atmosphere was highly reducing was challenged towards the end of the twentieth century, and is no longer the consensus view.

Although the significance of specific details of the Miller-Urey for the origin of life may now be in question, it began the new scientific discipline of prebiotic chemistry, and has been enormously influential in the development of ideas about the origin of life.

References:

"Origin Of Life: Twentieth Century Landmarks." Origin Of Life: Oparin-Haldane Hypothesis. N.p., n.d. Web. 28 Oct. 2012. < http://www.simsoup.info/Origin_Landmarks_Oparin_Haldane.html >.

"The Miller/Urey Experiment." The Miller/Urey Experiment. N.p., n.d. Web. 28 Oct. 2012. < http://www.chem.duke.edu/~jds/cruise_chem/Exobiology/miller.html >.

Reece, Jane B., and Neil A. Campbell. Campbell Biology. Harlow: Pearson Education, 2011. Print.

• Book:Structural Biochemistry

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Learning Objectives

• Describe the requirements for the origin of life (carbon source, energy, segregate molecules from environment, hereditary mechanism)
• Describe the steps which led to the origin of life (organic molecules form, macromolecules polymerize, a hereditary mechanism develops, membrane-enclosed protocells form).
• Apply the principles of evolution by natural selection to pre-biotic scenarios.

The origin of life is a mystery, the ultimate chicken-and-egg conundrum ( R Service, 2015 ). When you and fellow students together discussed the defining characteristics of life , you probably included reproduction and hereditary information, transformation of energy, growth and response to the environment. You may also have said that, at least on Earth, all life is composed of cells, with membranes that form boundaries between the cell and its environment, and that cells were composed of organic molecules (composed of carbon, hydrogen, nitrogen, oxygen, phosphate, and sulfur – CHNOPS). The conundrum is that, on Earth today, all life comes from pre-existing life. Pasteur’s experiments disproved spontaneous generation of microbial life from boiled nutrient broth. No scientist has yet been able to create a living cell from organic molecules. So how could life have arisen on Earth, around 3.8 billion years ago ? (Keep in mind the scale of time we’re talking about here – the Earth is 4.6 billion years old, so it took almost a billion years for chemical evolution to result in biological life.) How can this question be addressed using the process of scientific inquiry?

Origin of life studies

Although scientists cannot directly address how life on Earth arose, they can formulate and test hypotheses about natural processes that could account for various intermediate steps, consistent with the geological evidence. In the 1920s, Alexander Oparin and J. B. S. Haldane independently proposed nearly identical hypotheses for how life originated on Earth. Their hypothesis is now called the Oparin-Haldane hypothesis, and the key steps are:

• formation of organic molecules, the building blocks of cells (e.g., amino acids, nucleotides, simple sugars)
• formation of polymers (longer chains) of organic molecules, that can function as enzymes to carry out metabolic reactions, encode hereditary information, and possibly replicate (e.g., proteins, RNA strands),
• formation of protocells; concentrations of organic molecules and polymers that carry out metabolic reactions within an enclosed system, separated from the environment by a semi-permeable membrane, such as a lipid bilayer membrane

The Oparin-Haldane hypothesis has been continually tested and revised, and any hypothesis about how life began must account for the 3 primary universal requirements for life: the ability to reproduce and replicate hereditary information; the enclosure in membranes to form cells; the use of energy to accomplish growth and reproduction.

1. How did organic molecules form on a pre-biotic Earth?

Miller-urey experiment.

Stanley Miller and Harold Urey tested the first step of the Oparin-Haldane hypothesis by investigating the formation of organic molecules from inorganic compounds. Their 1950s experiment produced a number of organic molecules, including amino acids, that are made and used by living cells to grow and replicate.

Miller-Urey experiment, Wikimedia Commons illustration by Adrian Hunter

Miller and Urey used an experimental setup to recreate what environmental conditions were believed to be like on early Earth. A gaseous chamber simulated an atmosphere with reducing compounds (electron donors) such as methane, ammonia and hydrogen. Electrical sparks simulated lightning to provide energy. In only about a week’s time, this simple apparatus caused chemical reactions that produced a variety of organic molecules, some of which are the basic building blocks of life, such as amino acids. Although scientists no longer believe that pre-biotic Earth had such a reducing atmosphere, such reducing environments may be found in deep-sea hydrothermal vents, which also have a source of energy in the form of the heat from the vents. In addition, more recent experiments – that used conditions that are thought to better reflect the conditions of early Earth – have also produced a variety of organic molecules including amino acids and nucleotides (the building blocks of RNA and DNA) ( McCollom, 2013 ).

The video below gives a nice overview of the rationale, setup, and findings from the Miller-Urey experiment (although it incorrectly overstates that Darwin showed that relatively simple creatures can gradually give rise to more complex creatures).

Organic molecules from meteors

Each day the Earth is bombarded with meteorites and dust from comets. Analyses of space dust and meteors that have landed on Earth have revealed that they contain many organic molecules. The in-fall of cometary dust and meteorites was far greater when the Earth was young (4 billion years ago). Many scientists believe that such extra-terrestrial organic matter contributed significantly to the organic molecules available at the time that life on Earth began. The figure below from Bernstein 2006 shows the 3 major sources of organic molecules on pre-life Earth: atmospheric synthesis by Miller-Urey chemistry, synthesis at deep-sea hydrothermal vents, and in-fall of organic molecules synthesized in outer space.

Fig 6 from M. Bernstein 2006, Prebiotic materials from on and off the early Earth

2. Formation of organic polymers

Given a high enough concentration of these basic organic molecules, under certain conditions these will link together to form polymers (chains of molecules covalently bonded together). For example, amino acids link together to form polypeptide chains, that fold to become protein molecules. Ribose, a 5-carbon sugar, can bond with a nitrogenous base and phosphate to a nucleotide. Nucleotides link together to form nucleic acids, like DNA and RNA. While this is accomplished now by enzymes in living cells, polymerization of organic molecules can also be catalyzed by certain types of clay or other types of mineral surfaces. Experiments testing this model have produced RNA molecules up to 50-units long, in only a 1-2 week period of time ( Ferris, 2006 ).

Enzymatic activity and hereditary information in one polymer: the RNA World hypothesis

The discovery by Thomas Cech that some RNA molecules can catalyze their own site-specific cleavage led to a Nobel prize (for Cech and Altman), the term “ ribozymes ” to denote catalytic RNA molecules, and the revival of a hypothesis that RNA molecules were the original hereditary molecules, pre-dating DNA. For origin-of-life researchers, here was the possibility that RNA molecules could both encode hereditary information, and catalyze their own replication. DNA as the first hereditary molecule posed real problems for origin-of-life researchers because DNA replication requires protein enzymes (DNA polymerases) and RNA primers (see page on DNA replication), so it’s difficult to envision how such a complex hereditary system could have evolved from scratch. With catalytic RNA molecules, a single molecule or family of similar molecules could potentially store genetic information and replicate themselves, with no proteins needed initially.

Populations of such catalytic RNA molecules would undergo a molecular evolution conceptually identical to biological evolution by natural selection. RNA molecules would make copies of each other, making mistakes and generating variants. The variants that were most successful at replicating themselves (recognize identical or very similar RNA molecules and most efficiently replicate them) would increase in frequency in the population of catalytic RNA molecules. The RNA world hypothesis envisions a stage in the origin of life where self-replicating RNA molecules eventually led to the evolution of a hereditary system in the first cells or proto-cells. A system of RNA molecules that encode codons to specify amino acids, and tRNA-like molecules conveying matching amino acids, and catalytic RNAs that create peptide bonds, would constitute a hereditary system much like today’s cells, without DNA.

At some point in the lineage leading to the Last Universal Common Ancestor, DNA became the preferred long-term storage molecule for genetic information. DNA molecules are more chemically stable than RNA (deoxyribose is more chemically inert than ribose). Having two complementary strands means that each strand of DNA can serve as a template for replication of its partner strand, providing some innate redundancy. These and possibly other traits gave cells with a DNA hereditary system a selective advantage so that all cellular life on Earth uses DNA to store and transmit genetic information.

Still, even today, ribozymes play universal and central roles in cellular information processing. The ribosome is a large complex of RNAs and proteins that reads the genetic information in a strand of RNA to synthesize proteins. The key catalytic activity, the formation of peptide bonds to link two amino acids together, is catalyzed by a ribosomal RNA molecule. The ribosome is a giant ribozyme. Since ribosomes are universal to all cells, such catalytic RNAs must have been present in the Last Universal Common Ancestor of all current life on Earth.

Visit the  http://exploringorigins.org/ribozymes.html page to view the first ribozyme from Tetrahymena, discovered by Tom Cech, and the structure of the ribosomal RNAs.

The  http://exploringorigins.org/nucleicacids.html page has videos of polymerization of RNA from nucleotides, template-directed RNA synthesis, and a model of RNA self-replication.

The video below explains the rationale behind the RNA world hypothesis and briefly describes some of the findings from different RNA world experiments.

3. Protocells: self-replicating and metabolic enzymes in a bag

All life on Earth is composed of cells. Cells have lipid membranes that separate their inner contents, the cytoplasm, from the environment. The lipid membranes allow cells to maintain high concentrations of molecules like nucleotides needed for self-replicating RNAs to function more efficiently. Cells also maintain large differences in concentration (concentration gradients) of ions across the membrane to drive transport processes and cellular energy metabolism.

Lipids are hydrophobic, and will spontaneously self-assemble in water to form either micelles or lipid bilayer vesicles. Vesicles that enclose self-replicating RNAs and other enzymes, take in reactants across the membrane, export products, grow by accretion of lipid micelles, and divide by fission of the vesicle, are called proto-cells or protobionts and may have been the precursors of cellular life.

See http://exploringorigins.org/protocells.html for video animations of proto-cells.

The video below explores the differences between chemical and biological evolution, and highlights proto-cells as an example of chemical evolution.

At what point would evolutionary processes, such as natural selection, begin to drive the origin of the first cells?

Biological evolution is restricted to living organisms. So once the first cells, complete with a hereditary system, were formed, they would be subject to evolutionary processes, and natural selection would drive adaptation to their local environments, and populations in different environments would undergo speciation as gene flow becomes restricted between isolated populations.

However, the RNA World Hypothesis envisions evolutionary processes driving populations of self-replicating RNA molecules or proto-cells containing such RNA molecules. RNA molecules that replicated imperfectly would produce daughter molecules with slightly different sequences. The ones that replicate better, or improve the growth replication of their host proto-cells, would have more progeny. Hence, molecular evolution of self-replicating RNA molecules or proto-cell populations containing self-replicating RNA molecules would favor the eventual formation of the first cells.

References and Resources

Article on HCN chemistry by Patel et al. 2015  with Science News article by R. Service .

Bernstein M 2006. Prebiotic materials from on and off the early Earth. Philos Trans R Soc Lond B Biol Sci. 361:1689-700; discussion 1700-2. PubMed PMID: 17008210 ; PubMed Central PMCID: PMC1664678 .

Exploring Life’s Origins:  http://exploringorigins.org/index.html

UN Sustainable Development Goal (SDG) 3: Good Health and Well-being –    The origin of life and the steps leading up to it are important topics of research in the field of astrobiology, which seeks to understand the conditions necessary for the emergence of life. Understanding the origin of life can provide insight into the fundamental processes that govern the development and evolution of living organisms, which can have implications for human health and well-being. For example, research into the origin of life and evolutionarily novel traits can lead to the development of new treatments for diseases, as well as the creation of new medicines and therapies.

4 Responses to Origin of Life on Earth

Here’s a link to a fun article on work by Georgia Tech’s Nick Hud using a $5 toaster oven for his origin-of-life research! http://nautil.us/issue/27/dark-matter/the-dawn-of-life-in-a-5-toaster-oven Thanks to Timothy for the find and the link

New paper reveals likely traits of the Last Universal Common Ancestor of all extant life: Weiss et al. 2016: The physiology and habitat of the last universal common ancestor, Nature Microbiology 1, Article number: 16116 doi:10.1038/nmicrobiol.2016.116 James McInerney wrote a brief commentary for the above article: http://www.nature.com/articles/nmicrobiol2016139

Fantastic (somewhat long) retelling of origin-of-life research, with the twist and turns, culminating with the current integrated hypotheses. http://www.bbc.com/earth/story/20161026-the-secret-of-how-life-on-earth-began

A new paper going beyond the Miller-Urey types of expts to explore what could emerge out of these prebiotic chemistries: Wolos et al 2020, Synthetic connectivity, emergence, and self-regeneration in the network of prebiotic chemistry https://science.sciencemag.org/content/369/6511/eaaw1955

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Preface: The origin of life and astrobiology

Charles Darwin is historically renowned for his theory of evolution as the basis of variation of biological life that exists around us. Similar views were also echoed by the contemporary biologist, Alfred Russel Wallace, who is credited with independently conceiving the theory of evolution through natural selection. His paper on the subject was jointly published with some of Charles Darwin's writings in 1858. Despite strong opposition of the contemporary Christian Church of the time, gradually the natural selection theory for the biological evolution was accepted and remains pivotal to explain both inter- and intraspecies variation. However, a small section of theologists, philosophers and biologists continue to hold different views for the origin of life and its developments into numerous species and variation. Both schools, however, believe and acknowledge the genetic basis of life within the realms of nucleic acids, the ribose nucleic acid (RNA) and the deoxyribose nucleic acid (DNA). The fundamental questions remain—what must have been the earliest form of life on Earth? What is the relationship to life beyond Earth, if it exists at all?

Molecular biologists agree that the earliest form of life must have been based on the RNA molecule, with DNA evolving later following successive chemical processes to facilitate the RNA functions. It is argued that the earliest life would have been heterotrophic, arising from and metabolically processing prebiotic organics as proposed in the Oparin-Haldane theory. In this context, it is important to consider the abiogenesis theory that life on Earth arose from nonlife more than 4 billion years ago. Abiogenesis proposes that the original life forms were very simple and gradually became increasingly complex. It probably preceded biogenesis, in which life is derived from the procreation of other life. Abiogenesis became impossible once the present composition of the Earth was achieved. The abiogenesis theory is neither proved nor disproved. The cosmic origins of life discussed in the many articles in this volume remains at the forefront of modern discussions.

In the 1920s, the famous British biometric scientist John Haldane and Aleksandr Oparin, the Russian biochemist independently set forth similar ideas for the origin of life on Earth. Both believed that organic molecules could be formed from abiogenic materials in the presence of an external energy source, for example the ultraviolet radiation, in combination with very low atmospheric oxygen, ammonia, water vapor, and probably other gases. Both agreed that the earliest form of life probably first appeared in the warm oceans of Earth and were heterotrophic, nurtured by preformed nutrients from chemicals in existence on early Earth, or brought in by comets compared to being autotrophic, generating food and nutrients from complex interactions of the sunlight, including cosmic radiations with inorganic materials. Oparin believed that the life developed from microscopic spontaneously formed spherical lipid molecules held together by electrostatic forces, probably the earliest form of cells. These molecules most likely functioned as enzymes, essential for the biochemical metabolic reactions necessary for life's evolution. Haldane, unfamiliar with Oparin's theory, believed that simple organic molecules formed first and in the presence of ultraviolet light became increasingly complex, ultimately forming cells. Haldane and Oparin's ideas formed the foundation for much of the research on the origin of life, specifically formation of cells.

The Haldane-Oparin theory on the origin of life was tested to a limited extent by two American chemists, Harold Urey and Stanley Miller. They successfully produced organic molecules from some of the inorganic components thought to have been necessary for the appearance of life, the prebiotic phase. The Miller-Urey experiment included combination of warm water with a mixture of water vapor, methane, ammonia, and molecular hydrogen exposed to the atmospheric electrical discharges in the form of lightening. Miller and Urey found that simple organic molecules, including amino acids (the building blocks of peptides), had formed under the simulated conditions of early Earth. The Miller-Urey experiment demonstrated that organic molecules could form from abiogenic materials under the constraints of Earth's prebiotic atmosphere. Later research showed that amino acids can spontaneously form small protein molecules (peptides). It is also shown that the RNA molecule can be artificially synthesized from nucleotides (nitrogen containing compounds or bases) linked to sugar and phosphate groups. In fact, in addition to carrying and translating genetic information, RNA acts like a catalyst, a molecule that increases the rate of a reaction without itself being consumed. It is, thus, logical to accept that multiple forms of RNA existed in the prebiotic phase of abiogenesis that led to the formation of life on Earth or in any wider context.

It has been suggested that peptide nucleic acid (PNA) might have been the first genetic material that preceded the RNA and DNA. PNA forms very stable double helical structures and even stable triple helices. However, the chemical nature of PNA does not allow it be a sustainable genetic material necessary for replication, transfer of genetic information or its reorganization. Activated PNA monomers tend to cyclize easily and thus formation of oligomers is very difficult under prebiotic conditions. Further, and PNA hydrolyses rather rapidly and thus restricts the chances of it ever being accumulated in sufficient quantity, for instance deep in the primitive oceans.

The concept of sunlight (ultraviolet radiation) and energy sources from other planets in the cosmos (cosmic radiations) influencing the origin of life on Earth, or indeed anywhere in the cosmos, falls within the field of Astrobiology. The main question remains on the likelihood of the existence of life beyond the confines of Earth or perhaps in the wider cosmos. Astrobiology deals with the processes that may lead to the origin and evolution of life on Earth. Scientists continue to focus first on sites for understanding the processes of chemical (prebiotic) evolution (Titan, asteroids, and comets) and second on targets for searching for life beyond Earth (Mars, Venus, Europa, Enceladus, and others). Mars is one of the most popular targets due to the fact that early Mars and early Earth had a similar history. The quest for life on Mars is one of the most important missions of the modern astrobiology. Several ethicists and philosophers have strong reservations in relation to ethical, social and legal concerns that fall within the new discipline of astrobioethics . Perhaps the main stumbling block of research in life on Mars is the anticipation of a close similarity to life on Earth.

Most astrobiologists are guided by the following broad requirements and principles on the origin of life:

• (1) The elements of life, carbon, hydrogen, oxygen, and nitrogen (CHON).
• (2) CHON + energy (e.g., UV from stars, atmospheric lightning discharge) = monomers (Miller-Urey micromolecules).
• (3) Monomers + aqueous environment (to protect prebiotic organics from destruction by UV) + concentration/assembly/ordering = polymers.
• (4) Some such polymers presumably incorporated both gene-like information and enzyme-like catalytic activity (ribozymes). The information content in the enzymes being of a super-astronomical magnitude opens the way to the concept of a cosmological origin of life and the ideas of panspermia discussed by Sir Fred Hoyle and Prof. Chandra Wickramasinghe.
• (5) Earliest life, wherever it started, would thus have been heterotrophic and thermophilic.

The concept of cosmic genetic evolution emerged from discussions with the guest editors of this thematic volume. It is an extension of astrobiology to explore the extent of ultraviolet radiation (sunlight) and range of complex cosmic radiation systems implicated in genetic or genomic variation and function. The cosmic radiations (cosmic rays) include high-energy protons and atomic particles (nuclei) which move through space at nearly the speed of light. They originate from the sun, from outside of the solar system, supernova explosions of star, and from distant galaxies. These pass through the ozone layer and upon impact with the Earth's atmosphere, cosmic rays can produce cascade of secondary particles capable of striking the Earth's surface.

The fundamental questions remain:

• • Whether cosmic rays are capable of inducing spontaneous benign or deleterious genetic changes (mutations and variants)?
• • How far the cosmic ray phenomenon along with the introduction of new cosmic viruses could account for successive evolution of life on Earth?
• • Could cosmic radiation be an important factor in the emergence of different forms of biological life and variations?
• • How far does the impact of cosmic rays on the Earth might account for the creation of new viral variants capable of causing human disease, for example the Corona/Covid-19/SARS-CoV-2 virus?

The guest editors and other contributing authors have produced this impressive volume on a very unusual subject full of past and present hypotheses. Information and supporting arguments are most relevant and will form the basis for further discussion and design of new experiments and investigations. They all deserve to be congratulated on this exciting achievement. Now authors, editors and publishers shall wait for acceptance and appreciation of this unique contribution to the genetics literature.

Disclaimer and acknowledgements

This article is based on author's own perceptions, understanding and amateur knowledge of cosmology and astrobiology. Some of the ideas and concepts are derived from author's informal discussions with Professor Chandra Wickramasinghe, the Co-Editor of this thematic volume. His thoughtful insights and guidance are greatly appreciated. The author prefers to avoid add literature references as the subject is widely discussed in diverse digital open access public domains.

The author would be delighted to deal with any questions or observations related to this article: [email protected] ; [email protected] .

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• Published: 15 October 2014

Origin of life: The first spark

• David Deamer 1  

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David Deamer welcomes a synthesis of what we know about the origins of life, as told by a master in the field.

In Search of Cell History: The Evolution of Life's Building Blocks

• Franklin M. Harold

Franklin Harold's In Search of Cell History is a wonderful book. Harold has for 60 years been an intelligent and clear-minded researcher and observer in the fields of cell and molecular biology. His book is a loving distillation of connections within the incredible diversity of life in the biosphere, framing one of biology's most important remaining questions: how did life begin?

This is also a personal account. Here is Harold musing after washing the dishes: “I look upon my work and see that it is good, and I have no doubt that the same need to find order in the universe motivates much of science.” Using this deceptively casual approach, he cleans up the vast untidy mess of biology and stacks the fundamental concepts in an orderly and creative way for readers to enjoy.

The content of each chapter can be found in any good undergraduate biology text, but Harold fits the information into a larger context, often in unexpected ways. For instance, he discusses geochemist Michael Russell's idea that physical processes in hydrothermal vents could produce proton gradients, in which one side of a barrier membrane is acidic, the other alkaline. The movement of protons across these gradients supplies energy to all life now, and perhaps did so even in the first primitive life. Harold also reveals how much biologists can learn from geologists about the history of life on Earth. For instance, liquid water appeared on Earth more than 4 billion years ago; half a billion years later, the first known microbes (now fossilized in Australian rock) appeared.

I do have a quibble. Harold argues that, notwithstanding the vast literature, progress has gone little beyond the findings of Soviet biochemist Alexander Oparin and British polymath J. B. S. Haldane more than 80 years ago, when they independently argued that Louis Pasteur's dictum 'All life from life' was wrong. Oparin and Haldane theorized that life may have emerged on a sterile prebiotic Earth through a series of chemical and physical processes.

I confess to being more optimistic than Harold. There has been extraordinary progress in understanding the principles by which life works at the molecular level, and that can be applied to the question of how life begins. Over the past eight decades, it has become clear that the basic molecules of life can be synthesized through well-understood chemical reactions. The Strecker synthesis, for instance, produced amino acids from methane, ammonia, hydrogen and water vapour in Stanley Miller's famous 1950s experiment testing the Oparin–Haldane hypothesis. Furthermore, amino acids, nucleobases and lipid-like molecules — the building blocks of life — are present in carbon-containing meteorites. That makes it entirely plausible that similar organic compounds were available on the prebiotic Earth, waiting to be caught up in whatever process led to life's beginning.

There is more. In the 1960s, biophysicist Alec Bangham discovered that phospholipids assemble into cell-sized compartments (liposomes), and chemist Leslie Orgel found that chemically activated nucleotides — the organic molecular subunits of nucleic acids — spontaneously combine, or polymerize, into short strands of RNA. We now understand how light energy is captured by green plants, that the molecule adenosine triphosphate (ATP) is the energy currency of all life and that enzymes such as polymerases use that energy to catalyse the polymerization of amino acids into proteins, and of nucleotides into nucleic acids. The molecular foundation of evolution became clear when DNA's structure and function were established by Francis Crick and James Watson in the 1950s and 1960s. Finally, we know how to encapsulate all those reactions in lipid compartments that mimic cell membranes, and several pioneering laboratories are taking the first steps towards fabricating microscopic systems of molecules that display the fundamental properties of life.

Harold writes about these topics, so it seems that we have made considerable progress after all. If we use a jigsaw puzzle as a metaphor, more than 80 years ago we opened the box and found hundreds of loose pieces; today, some of them have been correctly placed around the edges of the puzzle. We still cannot see the picture in the centre, but I am satisfied that we have the framework.

Thousands of young biologists work mostly on the narrowly defined problems that are the crux of successful grantsmanship. Harold's book is like a balloon that will let them rise above the trees for a while and look down to better understand the scope and shape of the forest — and perhaps then descend to pluck some low-hanging fruit. Senior scientists like myself will take pleasure in comparing perspectives with Harold's. This is, after all, a story to conjure with — that of how life began and evolved into eukaryotic cells, a hundred trillion of which compose the human body. No one can yet tell this story in its entirety, but Harold's book is a good place to start.

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David Deamer is chair of the department of biomolecular engineering at the University of California, Santa Cruz. His research concentrates on nanopore sequencing of nucleic acids. His most recent books are First Life and, co-edited with Jack Szostak, Origins of Life.,

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Early Life Theories: Primordial Soup

A 1950s experiment may show how life formed on Earth

• History Of Life On Earth
• Human Evolution
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• M.A., Technological Teaching and Learning, Ashford University
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The early atmosphere of the Earth was a reducing atmosphere, meaning there was little to no oxygen . The gases that mostly made up the atmosphere were thought to include methane, hydrogen, water vapor, and ammonia. The mixture of these gases included many important elements, like carbon and nitrogen, that could be rearranged to make amino acids . Since amino acids are the building blocks of proteins , scientists believe that combining these very primitive ingredients could have possibly led to organic molecules coming together on Earth. Those would be the precursors to life. Many scientists have worked to prove this theory.

Primordial Soup

The "primordial soup" idea came about when Russian scientist Alexander Oparin and English geneticist John Haldane each came up with the idea independently. It had been theorized that life started in the oceans. Oparin and Haldane thought that with the mix of gases in the atmosphere and the energy from lightning strikes, amino acids could spontaneously form in the oceans. This idea is now known as "primordial soup." In 1940, Wilhelm Reich invented the Orgone Accumulator to harness the primordial energy of life itself.

The Miller-Urey Experiment

In 1953, American scientists Stanley Miller and Harold Urey tested the theory. They combined the atmospheric gases in the amounts that early Earth's atmosphere was thought to contain. They then simulated an ocean in a closed apparatus.

With constant lightning shocks simulated using electric sparks, they were able to create organic compounds, including amino acids. In fact, almost 15 percent of the carbon in the modeled atmosphere turned into various organic building blocks in only a week. This groundbreaking experiment seemed to prove that life on Earth could have spontaneously formed from nonorganic ingredients .

Scientific Skepticism

The Miller-Urey experiment required constant lightning strikes. While lightning was very common on early Earth, it wasn't constant. This means that although making amino acids and organic molecules was possible, it most likely did not happen as quickly or in the large amounts that the experiment showed. This does not, in itself, disprove the hypothesis . Just because the process would have taken longer than the lab simulation suggests does not negate the fact building blocks could have been made. It may not have happened in a week, but the Earth was around for more than a billion years before known life was formed. That was certainly within the timeframe for the creation of life.

A more serious possible issue with the Miller-Urey primordial soup experiment is that scientists are now finding evidence that the atmosphere of early Earth was not exactly the same as Miller and Urey simulated in their experiment. There was likely much less methane in the atmosphere during Earth's early years than previously thought. Since methane was the source of carbon in the simulated atmosphere, that would reduce the number of organic molecules even further.

Significant Step

Even though primordial soup in ancient Earth may not have been exactly the same as in the Miller-Urey experiment, their effort was still very significant. Their primordial soup experiment proved that organic molecules—the building blocks of life—can be made from inorganic materials. This is an important step in figuring out how life began on Earth.

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• Early Life Theories - Panspermia Theory
• Understanding Chemical Evolution
• The Oxygen Revolution
• Questions to Ask Your Biology Teacher About Evolution
• Early Life Theories - Hydrothermal Vents
• Life on Earth During the Precambrian Time Span
• What Are the Elements in the Human Body?
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• 10 Worst Greenhouse Gases
• The Four Eras of the Geologic Time Scale
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• Icon 1 — The Miller-Urey Experiment

The experiment itself

The understanding of the origin of life was largely speculative until the 1920s, when Oparin and Haldane, working independently, proposed a theoretical model for "chemical evolution." The Oparin-Haldane model suggested that under the strongly reducing conditions theorized to have been present in the atmosphere of the early earth (between 4.0 and 3.5 billion years ago), inorganic molecules would spontaneously form organic molecules (simple sugars and amino acids). In 1953, Stanley Miller, along with his graduate advisor Harold Urey, tested this hypothesis by constructing an apparatus that simulated the Oparin-Haldane "early earth." When a gas mixture based on predictions of the early atmosphere was heated and given an electrical charge, organic compounds were formed ( Miller, 1953 ; Miller and Urey, 1959 ). Thus, the Miller-Urey experiment demonstrated how some biological molecules, such as simple amino acids, could have arisen abiotically, that is through non-biological processes, under conditions thought to be similar to those of the early earth. 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 boils off

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, 1999 ; Hanic et al., 2000 ). 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.g., Kobayashi et al., 1998 ), high temperature impact events (e.g., Miyakawa et al., 2000 ), and even the action of waves on a beach ( Commeyras, et al., 2002 ) would have been quite effective.

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, 1998a ). 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 does not mention extraterrestrial sources of organic molecules, which have been widely discussed in the literature since 1961 (see Oró, 1961 ; Whittet, 1997 ; Irvine, 1998 ). Wells apparently missed the vast body of literature on organic compounds in comets (e.g. Oró, 1961 ; Anders, 1989 ; Irvine, 1998 ), carbonaceous meteorites (e.g. Kaplan et al., 1963 ; Hayes, 1967 ; Chang, 1994; Maurette, 1998 ; Cooper et al., 2001 ), and conditions conducive to the formation of organic compounds that exist in interstellar dust clouds ( Whittet, 1997 ).

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.g., Chang, 1994 ), at hydrothermal vents (e.g., Andersson, 1999 ; Ogata et al., 2000 ), and in volcanic aquifers ( Washington, 2000 ). A cursory review of the literature finds more than 40 papers on terrestrial prebiotic chemical synthesis published since 1997 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 2000 :18). 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, 2001 ) and therefore oxygen could not have played a role in preventing chemical synthesis. This conclusion is based on many sources of data , not "dogma." Sources of data include fluvial uraninite sand deposits ( Rasmussen and Buick, 1999 ) and banded iron formations ( Nunn, 1998 ; Copley, 2001 ), which could not have been deposited under oxidizing conditions. 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, 1994 ). Reduced paleosols suggest that oxygen levels were very low before 2.1 billion years ago ( Rye and Holland, 1998 ). There are also data from mantle chemistry that suggest that oxygen was essentially absent from the earliest atmosphere ( Kump et al. 2001 ). Wells misrepresents the debate as over whether oxygen levels were 5/100 of 1%, which Wells calls "low," or 45/100 of 1%, which Wells calls "significant." But the controversy is really over why it took so long for oxygen levels to start to rise. Current data show that oxygen levels did not start to rise significantly until nearly 1.5 billion years after life originated ( Rye and Holland, 1998 ; Copley, 2001 ). 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 3.0 billion years ago. They are irrelevant, as chemical data suggest that life arose 3.8 billion years ago ( Chang, 1994 ; Orgel, 1998b ), well before there was enough free oxygen in the earth's atmosphere to prevent Miller-Urey-type chemical synthesis.

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. Other theories have been proposed to bridge the gap between the organic "building blocks" and life. The "liposome" theory deals with the origin of cellular membranes, the RNA-world hypothesis deals with the origin of a simple genetic code, and the PNA (peptide-based genetics) theory proposes an even simpler potential genetic code ( Rode, 1999 ). Wells doesn't really mention any of this except to suggest that the "RNA world" hypothesis was proposed to "rescue" the Miller-Urey experiment. No one familiar with the field or the evidence could make such a fatuous and inaccurate statement. The Miller-Urey experiment is not relevant to the RNA world, because RNA was constructed from organic "building blocks" irrespective of how those compounds came into existence ( Zubay and Mui, 2001 ). The evolution of RNA is a wholly different chapter in the story of the origin of life, one to which the validity of the Miller-Urey experiment is irrelevant.

What the textbooks say

All of the textbooks reviewed contain a section on the Miller-Urey experiment. This is not surprising given the experiment's historic role in the understanding of the origin of life. The experiment is usually discussed over a couple of paragraphs (see Figure 2 ), a small proportion (roughly 20%) of the total discussion of the origin and early evolution of life. Commonly, the first paragraph discusses the Oparin-Haldane scenario, and then a second outlines the Miller-Urey test of that scenario. All textbooks contain either a drawing or a picture of the experimental apparatus and state that it was used to demonstrate that some complex organic molecules (e.g., simple sugars and amino acids, frequently called "building blocks") could have formed spontaneously in the atmosphere of the early earth. Textbooks vary in their descriptions of the atmospheric composition of the early earth. Five books present the strongly reducing atmosphere of the Miller-Urey experiment, whereas the other five mention that the current geochemical evidence points to a slightly reducing atmosphere. All textbooks state that oxygen was essentially absent during the period in which life arose. Four textbooks mention that the experiment has been repeated successfully under updated conditions. Three textbooks also mention the possibility of organic molecules arriving from space or forming at deep-sea hydrothermal vents ( Figure 2 ). No textbook claims that these experiments conclusively show how life originated; and all textbooks state that the results of these experiments are tentative.

It is true that some textbooks do not mention that our knowledge of the composition of the atmosphere has changed. However, this does not mean that textbooks are "misleading" students, because there is more to the origin of life than just the Miller-Urey experiment. Most textbooks already discuss this fact. The textbooks reviewed treat the origin of life with varying levels of detail and length in "Origin of life" or "History of life" chapters. These chapters are from 6 to 24 pages in length. In this relatively short space, it is hard for a textbook, particularly for an introductory class like high school biology, to address all of the details and intricacies of origin-of-life research that Wells seems to demand. Nearly all texts begin their origin of life sections with a brief description of the origin of the universe and the solar system; a couple of books use a discussion of Pasteur and spontaneous generation instead (and one discusses both). Two textbooks discuss how life might be defined. Nearly all textbooks open their discussion of the origin of life with qualifications about how the study of the origin of life is largely hypothetical and that there is much about it that we do not know.

Wells's evaluation

As we will see in his treatment of the other "icons," Wells's criteria for judging textbooks stack the deck against them, ensuring failure. No textbook receives better than a D for this "icon" in Wells's evaluation, and 6 of the 10 receive an F. This is largely a result of the construction of the grading criteria. Under Wells's criteria (Wells 2000:251-252), any textbook containing a picture of the Miller-Urey apparatus could receive no better than a C, unless the caption of the picture explicitly says that the experiment is irrelevant, in which case the book would receive a B. Therefore, the use of a picture is the major deciding factor on which Wells evaluated the books, for it decides the grade irrespective of the information contained in the text! A grade of D is given even if the text explicitly points out that the experiment used an incorrect atmosphere, as long as it shows a picture. Wells pillories Miller and Levine for exactly that, complaining that they bury the correction in the text. This is absurd: almost all textbooks contain pictures of experimental apparatus for any experiment they discuss. It is the text that is important pedagogically, not the pictures. Wells's criteria would require that even the intelligent design "textbook" Of Pandas and People would receive a C for its treatment of the Miller-Urey experiment.

In order to receive an A, a textbook must first omit the picture of the Miller-Urey apparatus (or state explicitly in the caption that it was a failure), discuss the experiment, but then state that it is irrelevant to the origin of life. This type of textbook would be not only scientifically inaccurate but pedagogically deficient.

Why we should still teach Miller-Urey

The Miller-Urey experiment represents one of the research programs spawned by the Oparin-Haldane hypothesis. Even though details of our model for the origin of life have changed, this has not affected the basic scenario of Oparin-Haldane. The first stage in the origin of life was chemical evolution. This involves the formation of organic compounds from inorganic molecules already present in the atmosphere and in the water of the early earth. This spontaneous organization of chemicals was spawned by some external energy source. Lightning (as Oparin and Haldane thought), proton radiation, ultraviolet radiation, and geothermal or impact-generated heat are all possibilities.

The Miller-Urey experiment represents a major advance in the study of the origin of life. In fact, it marks the beginning of experimental research into the origin of life. Before Miller-Urey, the study of the origin of life was merely theoretical. With the advent of "spark experiments" such as Miller conducted, our understanding of the origin of life gained its first experimental program. Therefore, the Miller-Urey experiment is important from an historical perspective alone. Presenting history is good pedagogy because students understand scientific theories better through narratives. The importance of the experiment is more than just historical, however. The apparatus Miller and Urey designed became the basis for many subsequent "spark experiments" and laid a groundwork that is still in use today. Thus it is also a good teaching example because it shows how experimental science works. It teaches students how scientists use experiments to test ideas about prehistoric, unobserved events such as the origin of life. It is also an interesting experiment that is simple enough for most students to grasp. It tested a hypothesis, was reproduced by other researchers, and provided new information that led to the advancement of scientific understanding of the origin of life. This is the kind of "good science" that we want to teach students.

Finally, the Miller-Urey experiment should still be taught because the basic results are still valid. The experiments show that organic molecules can form under abiotic conditions. Later experiments have used more accurate atmospheric compositions and achieved similar results. Even though origin-of-life research has moved beyond Miller and Urey, their experiments should be taught. We still teach Newton even though we have moved beyond his work in our knowledge of planetary mechanics. Regardless of whether any of our current theories about the origin of life turn out to be completely accurate, we currently have models for the processes and a research program that works at testing the models.

How textbooks could improve their presentations of the origin of life

Textbooks can always improve discussions of their topics with more up-to-date information. Textbooks that have not already done so should explicitly correct the estimate of atmospheric composition, and accompany the Miller-Urey experiment with a clarification of the fact that the corrected atmospheres yield similar results. Further, the wealth of new data on extraterrestrial and hydrothermal sources of biological material should be discussed. Finally, textbooks ideally should expand their discussions of other stages in the origin of life to include PNA and some of the newer research on self-replicating proteins. Wells, however, does not suggest that textbooks should correct the presentation of the origin of life. Rather, he wants textbooks to present this "icon" and then denigrate it, in order to reduce the confidence of students in the possibility that scientific research can ever establish a plausible explanation for the origin of life or anything else for that matter. If Wells's recommendations are followed, students will be taught that because one experiment is not completely accurate (albeit in hindsight), everything else is wrong as well. This is not good science or science teaching.

Table of Contents

• Icon 2 — Darwin's Tree of Life
• Icon 3 — Homology
• Icon 4 — Haeckel's Embryos
• Icon 5 — Archaeopteryx
• Icon 6 — Peppered Moths
• Icon 7 — Darwin's Finches
• Icons of Evolution? Conclusion
• Icons of Evolution? Figures
• Icons of Evolution? References
• "Icons" Critique — pdf versions
• Fatally Flawed Iconoclasm
• 10 Answers to Jonathan Wells's "10 Questions"

Origin Of Life: Twentieth Century Landmarks

The oparin-haldane hypothesis.

What do you think about us?

The Oparin-Haldane Hypothesis: A Framework for Understanding the Origin of Life

Concept map.

The Oparin-Haldane Hypothesis explores the origin of life through chemical evolution, from inorganic to organic compounds. It contrasts with spontaneous generation, suggesting a gradual process facilitated by a reducing atmosphere and external energy sources. The hypothesis is supported by the Miller-Urey Experiment and remains influential despite new insights questioning the nature of Earth's early atmosphere and proposing alternative theories like the RNA World Hypothesis.

The Oparin-Haldane Hypothesis

The Oparin-Haldane Hypothesis proposes that life began through a gradual chemical evolution from inorganic to organic compounds

Comparison to other theories

Abiogenesis

The Oparin-Haldane Hypothesis aligns with abiogenesis, which suggests that life arises from non-living matter

Spontaneous generation

The Oparin-Haldane Hypothesis refutes the outdated concept of spontaneous generation, which claimed that complex life could spontaneously arise from non-living matter

Supporting evidence

The Miller-Urey Experiment provided experimental support for the Oparin-Haldane Hypothesis by demonstrating that organic compounds could be synthesized from inorganic precursors under conditions thought to be similar to those of early Earth

Conditions for the Origin of Life

Primitive earth atmosphere.

The Oparin-Haldane Hypothesis suggests that the first life forms likely developed in a reducing atmosphere consisting of gases like methane, ammonia, and hydrogen, but lacking free oxygen

Ocean as a "primordial soup"

The Oparin-Haldane Hypothesis proposes that the oceans served as a vast, nutrient-rich environment for the formation of the earliest life forms

Heterotrophic organisms

The earliest life forms were likely heterotrophic, consuming organic molecules dissolved in the water, rather than producing their own food through photosynthesis

Mechanisms for the Formation of Life

Coacervates.

Oparin proposed that coacervates, aggregates of organic molecules surrounded by water, were precursors to living cells

Role of ultraviolet radiation

Haldane emphasized the role of ultraviolet radiation as an energy source that could drive the synthesis of organic compounds from simpler chemicals

Revisions and Alternative Theories

Reexamination of atmospheric conditions.

Recent geochemical evidence has prompted scientists to question the original concept of a reducing atmosphere proposed by the Oparin-Haldane Hypothesis

RNA World Hypothesis

The RNA World Hypothesis suggests that self-replicating RNA molecules were key to the development of early life, providing an alternative scenario to the Oparin-Haldane Hypothesis

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Proponents of Oparin-Haldane Hypothesis

Aleksandr Oparin and J. B. S. Haldane independently proposed the hypothesis.

Abiogenesis vs. Biogenesis

Abiogenesis: life from non-living matter; Biogenesis: life from existing life.

Spontaneous Generation vs. Oparin-Haldane

Spontaneous Generation: outdated idea of life from non-life without process; Oparin-Haldane: gradual chemical evolution.

______, coined by ______ ______ ______, is the process where life emerges from non-living matter, like simple organic compounds.

Abiogenesis Thomas Henry Huxley

The belief that complex organisms could emerge suddenly from non-living materials is known as ______ ______, which has been debunked by experiments like those of ______ ______.

spontaneous generation Francesco Redi

Primitive Earth atmosphere composition according to Oparin and Haldane

Consisted of methane, ammonia, hydrogen; lacked free oxygen.

Oparin-Haldane's location for first life forms

Life likely originated in nutrient-rich oceans, termed 'primordial soup'.

Earliest organisms' nutrition method per Oparin-Haldane

First organisms were heterotrophic, consuming organic molecules in water.

______ and ______ concurred on the essential environmental conditions for the emergence of life but had distinct theories for the initial life forms' creation.

Oparin Haldane

Miller-Urey Experiment Year

Gases Used in Miller-Urey Experiment

Methane, Ammonia, Hydrogen, Water Vapor

Significance of Electrical Sparks in Miller-Urey Experiment

Simulated Lightning, Triggered Chemical Reactions

The ______ World Hypothesis posits that self-replicating ______ molecules played a crucial role in the emergence of early life.

Oparin-Haldane Hypothesis - Core Concept

Chemical evolution as gradual, stepwise process leading to life.

Oparin-Haldane Hypothesis - Research Significance

Serves as historical, conceptual benchmark in origin-of-life studies.

Oparin-Haldane Hypothesis - Challenges

Faced scrutiny, yet pivotal in shaping subsequent theories, experiments.

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What is the essence of the oparin-haldane hypothesis regarding the origin of life, how do abiogenesis and spontaneous generation differ in the context of life's origin, what conditions did oparin and haldane believe were crucial for the emergence of life on earth, did oparin and haldane agree on the mechanisms for the formation of early life, how did the miller-urey experiment support the oparin-haldane hypothesis, what revisions have been made to the oparin-haldane hypothesis based on new scientific evidence, how has the oparin-haldane hypothesis impacted modern origin-of-life research, similar contents, explore other maps on similar topics.

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Exploring the Oparin-Haldane Hypothesis on Life's Origin

Distinguishing Abiogenesis from Spontaneous Generation

The primordial environment and the emergence of life, varied mechanisms in the formation of early life, experimental validation through the miller-urey experiment, reassessing the oparin-haldane hypothesis with new insights, the enduring influence of the oparin-haldane hypothesis.

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State two postulates of Orparin and Haldane with reference to origin of life.

Oparin and haldane proposed that the life has been originated by the chemical reactions in an aqueous environment. the postulates proposed by him are: the molecules present in the aqueous environment come together to form coacervates or aggregates. hydrogen gas served as a reducing agent while methane provided hydrocarbon skeleton for synthesis of organic compounds and the oxygen gas was absent..

Short / Long answer type questions . Describe in brief the Oparin-Haldane theory of origin of life.

Primordial Soup

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Prebiotic soup ; Primitive broth

The primordial soup is a generic term that describes the aqueous solution of organic compounds that accumulated in primitive water bodies of the early Earth as a result of endogenous abiotic syntheses and the extraterrestrial delivery by cometary and meteoritic collisions, and from which some have assumed that the first living systems evolved.

The term “primordial soup” and its synonyms are linked to the proposal of the heterotrophic theory of the origin of life, which was suggested independently in the 1920s by Alexander I. Oparin, John B. S. Haldane, and few others. Based on the simplicity and ubiquity of fermentative reactions, Oparin and Haldane proposed that the first organisms must have been heterotrophic bacteria that could not make their own food but obtained organic material present in the primitive milieu. In order to support his proposal, Oparin appealed not only to astronomical observations that had shown that...

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References and Further Reading

Bada J, Lazcano A (2002) Some like it hot, but not biomolecules. Science 296:1982–1983

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Bada JL, Lazcano A (2003) Prebiotic soup: revisiting the Miller experiment. Science 300:745–746

Bada JL, Lazcano A (2009) The origin of life. In: Ruse M, Travis J (eds) The harvard companion of evolution. Belknap/Harvard University Press, Cambridge, pp 49–79

Bernal JD (1944) The physical basis of life. Routledge and Kegan Paul, London

Calvin M (1969) Chemical evolution: molecular evolution towards the origin of living systems on the earth and elsewhere. Oxford University Press, New York

Chyba CF, Sagan C (1992) Endogenous production, exogenous delivery, and impact-shock synthesis or organic compounds, an inventory for the origin of life. Nature 355:125–132

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Cleaves JH, Chalmers JH, Lazcano A, Miller SL, Bada JL (2008) Prebiotic organic synthesis in neutral planetary atmospheres. Orig Life Evol Biosph 38:105–155

Cody GD, Boctor NZ, Filley TR, Hazen RM, Scott JH, Sharma A, Yoder HS Jr (2000) Primordial carbonylated iron-sulfur compounds and the synthesis of pyruvate. Science 289:1337–1340

Darwin F (ed) (1887) The life and letters of Charles Darwin, including an autobiographical chapter, vol 3. Murray, London

Farley J (1977) The spontaneous generation controversy from descartes to oparin. John Hopkins University Press, Baltimore/London

Haldane JBS (1929) The origin of life. Rationalist Annu 148:3–10

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Huber C, Wächtershäuser G (1997) Activated acetic acid by carbon fixation on, Fe, Ni, S under primordial conditions. Science 276:245–247

Huber C, Wächtershäuser G (1998) Peptides by activation of amino acids with CO on Ni, Fe, S surfaces and implications for the origin of life. Science 281:670–672

Lazcano A (2010a) Historical development of origins of life. In: Deamer DW, Szostak J (eds) Cold spring harbor perspectives in biology: the origins of life. Cold Spring Harbor Press, Cold Spring Harbor, pp 1–16

Lazcano A (2010b) The origin and early evolution of life: did it all start in Darwin’s warm little pond? In: Bell MA, Futuyma DJ, Eanes WF, Levinton JS (eds) Evolution since Darwin: the first 150 years. Sinauer, Sunderland, pp 353–375

Maden BEH (1995) No soup for starters? Autotrophy and origins of metabolism. Trends Biochem Sci 20:337–341

Miller SL (1953) A production of amino acids under possible primitive Earth conditions. Science 117:528

Miller SL, Lazcano A (2002) Formation of the building blocks of life. In: Schopf JW (ed) Life’s origin: the beginnings of biological evolution. California University Press, Berkeley, pp 78–112

Oparin AI (1924) Proiskhozhedenie Zhizni. Mosckovskii Rabochii, Moscow. Reprinted and translated in Bernal JD (1967) The origin of life. Weidenfeld and Nicolson, London

Oparin AI (1938) The origin of life. McMillan, New York

Peretó J, Bada JL, Lazcano A (2009) Charles Darwin and the origins of life. Orig Life Evol Biosph 39:395–406

Podolsky S (1996) The role of the virus in origin-of-life theorizing. J Hist Biol 29:79–126

Urey HC (1952) On the early chemical history of the earth and the origin of life. Proc Natl Acad Sci U S A 38:351–363

Wächtershäuser G (1988) Before enzymes and templates, theory of surface metabolism. Microbiol Rev 52:452–484

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Facultad de Ciencias, UNAM, Cd. Universitaria, Mexico, DF, Mexico

Antonio Lazcano

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CNRS-Universite de Bordeaux, Laboratoire d’Astrophysique de Bordeaux, Floirac, France

Muriel Gargaud

University of Massachusetts, Amherst, MA, USA

William M. Irvine

Departamento de Biologia Molecular, Universidad Autónoma de Madrid, Madrid, Spain

Ricardo Amils

Earth–Life Science Institute (ELSI), Tokyo Institute of Technology, Meguro–ku, Tokyo, Japan

Henderson James (Jim) Cleaves II

GEOTOP Research Center for Geochemistry and Geodynamics, Université du Québec à Montréal, Montréal, QC, Canada

Daniele L. Pinti

Department of Astrophysics, Laboratory of Molecular Astrophysics, Iorrejón de Ardoz, Madrid, Spain

José Cernicharo Quintanilla

LESIA, Observatoire Paris-Site de Meudon, Meudon, France

Daniel Rouan

Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Berlin, Germany

Tilman Spohn

Centre François Viéte d'Histoire des Sciences et des Techniques EA 1161, Faculté des Sciences et des, Techniques de Nantes, Nantes, France

Stéphane Tirard

CNES/DSP/SME, Vétérinaire/DVM, Astro/Exobiology, Paris Cedex 1, France

Michel Viso

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Lazcano, A. (2015). Primordial Soup. In: Gargaud, M., et al. Encyclopedia of Astrobiology. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-44185-5_1275

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Coordinates of Elektrostal in decimal degrees

Coordinates of elektrostal in degrees and decimal minutes, utm coordinates of elektrostal, geographic coordinate systems.

WGS 84 coordinate reference system is the latest revision of the World Geodetic System, which is used in mapping and navigation, including GPS satellite navigation system (the Global Positioning System).

Geographic coordinates (latitude and longitude) define a position on the Earth’s surface. Coordinates are angular units. The canonical form of latitude and longitude representation uses degrees (°), minutes (′), and seconds (″). GPS systems widely use coordinates in degrees and decimal minutes, or in decimal degrees.

Latitude varies from −90° to 90°. The latitude of the Equator is 0°; the latitude of the South Pole is −90°; the latitude of the North Pole is 90°. Positive latitude values correspond to the geographic locations north of the Equator (abbrev. N). Negative latitude values correspond to the geographic locations south of the Equator (abbrev. S).

Longitude is counted from the prime meridian ( IERS Reference Meridian for WGS 84) and varies from −180° to 180°. Positive longitude values correspond to the geographic locations east of the prime meridian (abbrev. E). Negative longitude values correspond to the geographic locations west of the prime meridian (abbrev. W).

UTM or Universal Transverse Mercator coordinate system divides the Earth’s surface into 60 longitudinal zones. The coordinates of a location within each zone are defined as a planar coordinate pair related to the intersection of the equator and the zone’s central meridian, and measured in meters.

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Elektrostal , Moscow Oblast, Russia