Chemical Evolution and the Origin of Life

Up to now, we do not have a generally accepted theory about the origin of life and about the process of development of life, we only have a great number of - to .
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The next step in chemical evolution suggests that polymers interacted with each other and organized into aggregates, known as protobionts. Protobionts are not capable of reproducing, but had other properties of living things. Scientists have successfully produced protobionts from organic molecules in the laboratory. In one study, proteinoids mixed with cool water assembled into droplets or microspheres that developed membranes on their surfaces.

These are protobionts, with semipermeable and excitable membranes, similar to those found in cells. In the final step of chemical evolution, protobionts developed the ability to reproduce and pass genetic information from one generation to the next. Some scientists theorize RNA to be the original hereditary molecule. Short polymers of RNA have been synthesized abiotically in the laboratory.

This implies that RNA molecules could have replicated in prebiotic cells without the use of protein enzymes.

Chemical Evolution - The primitive Earth

Variations of RNA molecules could have been produced by mutations and by errors during replication. Natural selection , operating on the different RNAs would have brought about subsequent evolutionary development. This would have fostered the survival of RNA sequences best suited to environmental parameters, such as temperature and salt concentration.

As the protobionts grew and split, their RNA was passed on to offspring.

Chemical evolution and the origin of life. - PubMed - NCBI

In time, a diversity of prokaryote cells came into existence. Under the influence of natural selection, the prokaryotes could have given rise to the vast variety of life on Earth. The chemical and physical conditions of the primitive Earth are invoked to explain the origin of life, which was preceded by chemical evolution of organic chemicals. Astronomers believe that billion years ago, all matter was concentrated in a single mass, and that it blew apart with a "big bang. Please include a link to this page if you have found this material useful for research or writing a related article.

Content on this website is from high-quality, licensed material originally published in print form. You can always be sure you're reading unbiased, factual, and accurate information. Paste the link into your website, email, or any other HTML document. Your email address will be altered so spam harvesting bots can't read it easily. Hide my email completely instead? It was all energy, that has been converted to matter in various forms over time. To say it 'blew apart' indicates an explosion in some people's minds.

It was a rapid expansion OF space and time, and not an explosion IN space and time. They used a warmed flask of water for the ocean, and an atmosphere of water, hydrogen, ammonia and methane. I have a great deal of input into the chemicals of life discussion. Whoever is responsible for this page should contact me.

Wow, what an oversimplification. And how did it do that? The next sentence says that it was done in a lab, and I'm sure the people who designed the experiments were very intelligent cough! The simplest of proteins has over amino acids, all of which must be aligned precisely Here's a good link that discusses many of the problems I had with this article.

Origin of Life - Chemical Evolution (Part 1)

This information is in need of serious updating. The big band did NOT occur billion years ago. It is between 13 and 14 billion.

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I didn't want to read more because of this egregious error. I appreciate the effort but if I find an error this wrong I have to wonder about the rest of the information. It says early life has been found 3. Also it says the big band was billion years ago, but it was actually about 13 billion years ago. It sounds very believable. Maybe in the future scientists will try to evolve protobionts into actual bacteria in long term experiments involving the primordial stew, lightning, and ultraviolet radiation for mutations.

I'd like to point out that the universe is actually It is unlikely that Miller's artificial environment matched the exact composititon of the air in the actual primitive atmosphere at that time.


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The origin of life could not have been so simple. Chemical Evolution - The primitive Earth. According to one theory, chemical evolution occurred in four stages. Or the first life in the universe might have been totally unlike familiar carbon-based life on earth. Scientists are trying to develop principles for a prebiological selection of molecules, analogous to the biological selection of genes in living organisms.

And they are continuing to explore the self-organizing properties of complex chemical systems, and to search for ways of reducing the minimal complexity required for a living system. What is the status of these alternative theories? So far, none has progressed from speculation to plausibility. But they do stimulate experimental and theoretical research, and offer the hope that eventually scientists may discover new principles to serve as the basis for new theories, and may develop a plausible explanation.


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But the major reasons to question chemical evolution come from what we do know about chemistry and life, not from our lack of knowledge. The Biochemical Challenge to Evolution , Michael Behe illustrates the principle of irreducible complexity with a mousetrap that has five interacting parts: Each part is necessary, and there is no function unless all parts are present. A trap with only four parts has no practical function. It doesn't just catch mice poorly, it doesn't catch them at all.

What are the evolutionary implications? Behe says, "An irreducibly complex system cannot be produced directly An irreducibly complex biological system, if there is such a thing, would be a powerful challenge to Darwinian evolution. For the origin of life, we can think about the minimal complexity that would be required for reproduction and other basic life-functions. Most scientists think this would require hundreds of biomolecular parts, not just the five parts in a simple mousetrap.

Here is the original version from , with minor revisions before it was condensed: By contrast with this outdated theory, modern theories of chemical evolution propose that life formed in a process that might have been allowed by different conditions on the early earth when there was no molecular oxygen to interfere with the formation of organic chemicals and no existing life to out-compete or eat the less efficient newly-emerging primitive life forms, or to consume the organic chemicals from which life might emerge. Despite initial optimism following the famous Miller-Urey experiments in , since then a closer investigation of important details has revealed major scientific difficulties that have not been solved, and perhaps cannot be solved, at each step of the proposed natural process: In Miller's original experiments and in the variations that followed, many organic molecules were formed in small amounts.

But these early experiments used an unusually reactive mixture of ammonia, methane, and hydrogen, plus water vapor. Since then, scientists have concluded that the major molecules in the early atmosphere were nitrogen, carbon dioxide, and water vapor. When these less reactive chemicals are used, the yield of organic molecules is much lower and less varied than the small amounts in the earlier experiments. When we look at the proposal that these small molecules combined to form larger biomolecules, we find that in water these reactions are also energetically unfavorable.

And new difficulties arise. For example, during protein synthesis a prebiotic reaction mixture would contain many different chemicals L-amino acids and R-amino acids, plus a variety of more reactive molecules , and the majority of newly formed bonds would not be the special peptide bonds linking only L-amino acids that are found in natural proteins. The scarcity of peptide bonds is partly due to the fact that in a watery "soup" the formation of these bonds is energetically unfavorable.

Similar difficulties would arise in the prebiotic formation of other important biomolecules. Attempts to synthesize RNA — or even the smaller molecules such as ribose sugars that combine to form RNA — have been especially unsuccessful. Even if plenty of biomolecules could form in Stage 1b, these lifeless chemicals would have reached only the starting point for the most challenging part of their journey toward life -- organizing themselves into a living organism in Stage 2.

The simplest self-sustaining "living system" we can imagine, involving hundreds of components interacting in an organized way to achieve energy-producing metabolism and accurate self-replication, would be extremely difficult to assemble by undirected natural processes. It is important to remember that this self-assembly would have occurred before "Darwinian" natural selection was available. Therefore, molecules would have to organize themselves into a system that fulfills the minimum requirements for natural selection i. In Stage 1a, for example, since the early atmosphere seems unfavorable for Miller-Urey syntheses, perhaps organic compounds were imported from space by comets, meteorites, and interstellar dust.

And in Stage 2, an effort to avoid a tough "chicken and egg" problem — in modern cells, DNA is required for protein synthesis, but protein is required for DNA synthesis — inspired theories proposing that RNA which combines the replicating ability of DNA and, to a small degree, the catalytic activity of proteins was "the main molecule" in the earliest cells. This RNA World scenario now seems less appealing than when it was originally proposed, largely due to the apparent impossibility of RNA synthesis in prebiotic conditions, and also because RNA functionality catalytic activity, self-replicating ability, In response, recent theories have proposed a simpler pre-RNA World with key functional roles played by other molecules pantetheine or coenzyme A, pyranosyl RNA, Other alternatives include variations on the classic "soup" scenario, with new environments such as an isolated semi-evaporated pond, or a seafloor hydrothermal vent that might supply heat and sulfur compounds to serve as energy resources for primitive organisms.


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    • Or maybe the original biogenesis occurred in an extremely different environment -- on another planet. Or instead of limiting the possibilities to a self-contained cell in a watery organic soup, another theory proposes that inorganic clay-like minerals played an important function by interacting with organic molecules in the earliest forms of life. Or the first life might have been totally unlike familiar carbon-based organisms.

    Scientists are trying to develop principles of a prebiological "molecular selection" that was analogous to biological natural selection. Stanley Kaufmann speculates that within a complex mixture of chemicals there can be a spontaneous production of an organized autocatalytic network of reactions that is a self-replicating system, and the beginning of life. Their main practical functions are to provide ideas for continuing experimental and theoretical research, and to offer hope for proponents of chemical evolution.

    This hope takes two forms: These hopes are the basis for a conventional response to criticism: Or perhaps life did originate once by a natural mechanism, but this unique event was so unlikely and strange and therefore difficult for scientists to imagine that we will never develop a theory for natural abiogenesis even though it did occur in nature's history. On the other hand, if scientists do eventually construct a plausible theory for chemical-E, supported by experiments that create self-replicating "life", we should not abandon critical thinking.