The Origin of Life

Based on the March 1998 issue of

National Geographic Magazine

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What kind of place was primordial Earth?

The young sun shone

with only 70% of its present

power.

Four billion years ago…

The atmosphere held

no free oxygen.

There were few sounds beyond the wind, the hiss of lava hitting water,

the boom of meteorites.

No plants, no animals, no bacteria, no viruses.

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What kind of place was primordial Earth?

No one knows exactly what Earth was like when life began.

Rocks that may have held clues

were deformed long ago by the movements of the

crust.

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Did life begin in a ball of ice?• “The colder the

temperature, the more stable the compounds.”

• Interplanetary debris, hydrothermal vents, atmospheric reactions: formaldehyde, cyanide, ammonia.

•These then combine with water in a lattice of ice, resulting in glycine.

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Did life begin in a pond?

• Darwin and his contemporaries imagined life evolving in a small body of water.

•Compounds may have been concentrated on the surfaces of sheet-like minerals, which attract certain molecules and act as a catalyst for subsequent reactions.

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Did life begin in a cauldron?

• “Gases released from the molten magma would have been constantly seeping from the surface, leaching out vital compounds.”

•Resting on a stabilizing surface of pyrite, carbon monoxide and a methyl group combine, one step in the formation of activated acetic acid, a crucial chemical for synthesizing other organic compounds.

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Miller-Urey Experiment, 1953

Primeval atmosphere: CH4, H2, NH3

Early ocean

Lightning

•By sparking the atmosphere, Miller hoped to generate new chemicals that would rain into the tiny ocean and react to form something.

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Miller-Urey Experiment, 1953

•“I turned on the experiment one night at 10 p.m. Then I came back the next morning, and the water inside the flask had turned yellow.”

•What he had was a rich broth of amino acids, used by all known creatures as the building blocks for proteins.STANLEY MILLER

Father of Prebiotic Chemistry

7 Mar 1930 – 20 May 2007

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Miller-Urey Experiment, 1953

Primeval atmosphere: CH4, H2, NH3

Early ocean

Lightning

•Many scientists now suspect that the early atmosphere was different from what Miller first supposed.

CO2, N2***

*** CO2 + N2 = organic molecules Scientists find it hard to imagine life emerging from such a diluted soup.

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Help from outer space…

• A large variety of organic compounds, including those which play a major role in biochemistry such as amino acids, purines, pyrimidines, etc., have been identified in one class of meteorites, the carbonaceous chondrites.

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Definition of Life• Life is “…a self-

sustained chemical system capable of undergoing Darwinian evolution.” – Gerald Joyce, The Scripps Research Institute

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Definition of Life• Life is “…a self-

sustained chemical system capable of undergoing Darwinian evolution.” – Gerald Joyce, The Scripps Research Institute

Darwinian evolution:1. Able to reproduce by

making copies of themselves.

2. Copies must contain inheritable imperfections (mutations) that introduce variations into the population.

3. System of natural selection that favors survival of some individuals over others.

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Life begins to self-assemble

• Before DNA and proteins evolved, before even the simplest bacteria appeared, life may have consisted solely of RNA molecules floating in the sea, replicating, mutating, and undergoing natural selection on their own.

• As DNA and proteins evolved, these more specialized molecules took over most of the critical work from RNA.

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Cells take form• At some unknown point life found a home inside a

protective membrane, forming the very first cells.

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Global gas warfare• Stromatolites:

microorganisms (cyanobacteria) + rock

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The triumph of O2• Bacteria that use oxygen

generate energy far more efficiently than their oxygen-hating neighbors.– Fermentation: 2 molecules of

ATP from one molecule of sugar– Aerobic respiration: 36

molecules of ATP from one molecule of sugar

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The origin of sex• Asexual reproduction:

organisms make genetically identical copies of themselves.

• “With the evolution of sex you get a lot of genetic recombination, a lot of possibility for change.”- Andy Knoll, Harvard University

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The origin of sex• Asexual reproduction:

organisms make genetically identical copies of themselves.

• “With the evolution of sex you get a lot of genetic recombination, a lot of possibility for change.”- Andy Knoll, Harvard University

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The Origin of Life Made Easy• To view the video again on the Origin

of Life, go to http://www.youtube.com and search for “Origin of Life Made Easy”.

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Summary• The recurring idea throughout this discussion is that:

– right ingredients + right conditions spontaneous abiotic formation of organic compounds, (starting with monomers, which later polymerized, eventually forming the complex biomolecules that make up today’s living organisms)

• Recap – the trends in the evolution of living organisms are:– Unicellular before multicellular organisms– Heterotrophs before autotrophs– Anaerobic before aerobic– Asexual reproduction before sexual reproduction