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Chemical Evolution - The primitive Earth

atmosphere water life environment

Chemical evolution describes chemical changes on the primitive Earth that gave rise to the first forms of life. The first living things on Earth were prokaryotes with a type of cell similar to present-day bacteria. Prokaryote fossils have been found in 3.4-million-year-old rock in the southern part of Africa, and in even older rocks in Australia, including some that appear to be photosynthetic. All forms of life are theorized to have evolved from the original prokaryotes, probably 3.5-4.0 billion years ago.


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 20-30 billion years ago, all matter was concentrated in a single mass, and that it blew apart with a "big bang." In time, a disk-shaped cloud of dust condensed and formed the Sun, and the peripheral matter formed its planets. Heat produced by compaction, radiation, and impacting meteorites melted Earth. Then, as the planet cooled, Earth's layers formed. The first atmosphere was made up of hot hydrogen gas, too light to be held by Earth's gravity. Water vapor, carbon monoxide, carbon dioxide, nitrogen, and methane replaced the hydrogen atmosphere. As Earth cooled, water vapor condensed and torrential rains filled up its basins, thereby forming the seas. Also present were lightning, volcanic activity, and ultraviolet radiation. It was in this setting that life began.

According to one theory, chemical evolution occurred in four stages.

In the first stage of chemical evolution, molecules in the primitive environment formed simple organic substances, such as amino acids. This concept was first proposed in 1936 in a book entitled, "The Origin of Life on Earth," written by the Russian scientist, Aleksandr Ivanovich Oparin. He considered hydrogen, ammonia, water vapor, and methane to be components in the early atmosphere. Oxygen was lacking in this chemically-reducing environment. He stated that ultraviolet radiation from the Sun provided the energy for the transformation of these substances into organic molecules. Scientists today state that such spontaneous synthesis occurred only in the primitive environment. Abiogenesis became impossible when photosynthetic cells added oxygen to the atmosphere. The oxygen in the atmosphere gave rise to the ozone layer which then shielded Earth from ultraviolet radiation. Newer versions of this hypothesis contend that the primitive atmosphere also contained carbon monoxide, carbon dioxide, nitrogen, hydrogen sulfide, and hydrogen. Present-day volcanoes emit these substances.

In 1957, Stanley Miller and Harold Urey provided laboratory evidence that chemical evolution as described by Oparin could have occurred. Miller and Urey created an apparatus that simulated the primitive environment. They used a warmed flask of water for the ocean, and an atmosphere of water, hydrogen, ammonia and methane. Sparks discharged into the artificial atmosphere represented lightning. A condenser cooled the atmosphere, causing rain that returned water and dissolved compounds back to the simulated sea. When Miller and Urey analyzed the components of the solution after a week, they found various organic compounds had formed. These included some of the amino acids that compose the proteins of living things. Their results gave credence to the idea that simple substances in the warm primordial seas gave rise to the chemical building blocks of organisms.

In the second stage of chemical evolution, the simple organic molecules (such as amino acids) that formed and accumulated joined together into larger structures (such as proteins). The units linked to each other by the process of dehydration synthesis to form polymers. The problem is that the abiotic synthesis of polymers had to occur without the assistance of enzymes. In addition, these reactions give off water and would, therefore, not occur spontaneously in a watery environment. Sydney Fox of the University of Miami suggested that waves or rain in the primitive environment splashed organic monomers on fresh lava or hot rocks, which would have allowed polymers to form abiotically. When he tried to do this in his laboratory, Fox produced proteinoids—abiotically synthesized polypeptides.

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. In the 1980s, Thomas Cech and his associates at the University of Colorado at Boulder discovered that RNA molecules can function as enzymes in cells. This implies that RNA molecules could have replicated in prebiotic cells without the use of protein enzymes. 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. 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.

See also Amino acid.


Resources

Books

Keeton, William T., and James L. Gould. Biological Science. New York: W.W. Norton and Co., 1993.

Periodicals

Franklin, Carl. "Did Life Have a Simple Start?" New Scientist (October 2, 1993).

Radetsky, Peter. "How Did Life Start?" Discover (November 1992).


Bernice Essenfeld

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Abiogenesis

—Origin of living organisms from nonliving material.

Autotroph

—This refers to organisms that can synthesize their biochemical constituents using inorganic precursors and an external source of energy.

Heterotroph

—Organism that requires food from the environment since it is unable to synthesize nutrients from inorganic raw materials.

Prokaryote

—Type of cell that lacks a membraneenclosed nucleus. Found solely in bacteria.

Chemical Oxygen Demand [next] [back] Chemical Bond - History, The Origin Of Bond Symbolism, Development Of The Modern Theory Of Bonding, Bond Types

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about 2 years ago

Explain the Theory of Chemical Evolution on scientific basis

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over 5 years ago

hi,

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about 2 years ago

"Astronomers believe that 20-30 billion years ago, all matter was concentrated in a single mass, and that it blew apart with a "big bang." " Wrong.

13.7 billion years ago and there was no matter at that time. 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.

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over 5 years ago

wow!! conceptual.

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about 5 years ago

I have a great deal of input into the chemicals of life discussion. Whoever is responsible for this page should contact me.

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over 5 years ago

differentiate for me between chemical and biological evolution please

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over 3 years ago

Wow, what an oversimplification. "In the final step of chemical evolution, protobionts developed the ability to reproduce and pass genetic information from one generation to the next." Really? 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!), and yet still didn't create life. The simplest of proteins has over 250 amino acids, all of which must be aligned precisely... You know what? Here's a good link that discusses many of the problems I had with this article.
http://www.icr.org/article/origin-life-critique-early-stage-chemical-evolutio/

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over 6 years ago

1957, Stanley Miller and Harold Urey provided laboratory evidence that chemical evolution as described by Oparin could have occurred. Miller and Urey created an apparatus that simulated the primitive environment. They used a warmed flask of water for the ocean, and an atmosphere of water, hydrogen, ammonia and methane. Sparks discharged into the artificial atmosphere represented lightning. A condenser cooled the atmosphere, causing rain that returned water and dissolved compounds back to the simulated sea. When Miller and Urey analyzed the components of the solution after a week, they found various organic compounds had formed. These included some of the amino acids that compose the proteins of living things. Their results gave credence to the idea that simple substances in the warm primordial seas gave rise to the chemical building blocks of organisms.



Read more: Chemical Evolution - The primitive Earth - Atmosphere, Life, Water, Rna, Molecules, and Organic http://science.jrank.org/pages/1387/Chemical-Evolution.html#ixzz1KYjoJQjZ

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about 2 years ago

It says early life has been found 3.4 million years ago- I thing it meant billion? because homo species have been found that are older and the dinosaurs were way older than that. Also it says the big band was 20-30 billion years ago, but it was actually about 13 billion years ago

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over 2 years ago

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This makes no sense and i think it needs its grammar improved

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over 5 years ago

wow!! conceptual.

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over 5 years ago

wow!! conceptual.

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about 7 years ago

where from the oxygen came, is not clear to me.

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almost 3 years ago

wow

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over 5 years ago

differentiate for me between chemical and biological evolution please

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over 5 years ago

differentiate for me between chemical and biological evolution please

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over 6 years ago

good

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over 5 years ago

differentiate for me between chemical and biological evolution please

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over 2 years ago

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over 2 years ago

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almost 7 years ago

Very interesting theory. 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.

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about 3 years ago

This information is in need of serious updating. The big band did NOT occur 20-30 billion years ago. It is between 13 and 14 billion. 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.

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about 5 years ago

just wanted help with a question how has the activity of early prokaryotic organisms led to conditions favorable for evolution of higher life forms? could you reply to me as soon as possible.

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over 5 years ago

differentiate for me between chemical and biological evolution please

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almost 6 years ago

email me more of the this chemical evolutionary anda evolutionary.

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over 1 year ago

I'd like to point out that the universe is actually 13.82 billion years old, neither 20-30b years nor 13.73b years.
Proven by European Space Agency's Planck Mission.

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almost 2 years ago

It is unlikely that Miller's artificial environment matched the exact composititon of the air in the actual primitive atmosphere at that time. The origin of life could not have been so simple.

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5 months ago

id like salad on the side please

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almost 6 years ago

ohhh this is nice ;)

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over 2 years ago

its wonderfull

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over 5 years ago

wow!! conceptual.

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about 1 year ago

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2 months ago

Wow, this is being amazing!