WHERE DID THE FIRST LIVING THINGS COME FROM?

• Twenty years after Pasteur’s experiment, disproving spontaneous generation, Thomas Henry Huxley first used the term biogenesis.

• The concept of biogenesis is one of the most completely demonstrated principles in biology.

• For life to come into being, scientists agree that four developments MUST have occurred. These include the following:

1. The formation of simple organic compounds important to life.

2. The formation of complex organic compounds, such as proteins.

3. The concentration and enclosure of these organic compounds.

4. The linking of chemical reactions involved in growth

1.Formation of Simple Organic Compounds

• The Heterotroph Hypothesis:

In the 1930’s, the Russian scientist, A. I. Oparin, presented a hypothesis to explain how the first living thing might have developed. This theory was called the Heterotroph Hypothesis.

• He proposed that: a. Energy from ultraviolet light, lightning and volcanic

heat caused chemical reactions to occur in the atmosphere.

b. These reactions created small organic molecules that dissolved in oceans.

c. Eventually, a large quantity of organic chemicals accumulated.

d. According to Oparin, the first life must have evolved from these organic compounds.

• In the 1950’s Stanley Miller tried to recreate conditions on Earth under which life may have formed. He used:

-water to represent the oceans

-methane, ammonia, hydrogen and water vapor as the earth’s early atmosphere

-electrical sparks as lightning.

• After his experiment, he found numerous organic compounds including amino acids. Although amino acids are the building blocks of protein, Miller had NOT created life.

• He had shown that conditions like those on early Earth could produce some of the chemicals present in living things.

2. Formation of Complex Organic Compounds

*How could simple organic compounds have formed complex organic compounds essential for life?*

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-Some scientists have performed experiments that suggest that amino acids might have formed chains spontaneously in the early atmosphere.

- Other scientists have shown that amino acids will link up when heated in the absence of oxygen gas.

- Similar mechanisms might have led to the formation of carbohydrates, lipids, and nucleic acids.

3. Concentration and Enclosure of Organic Compounds

• Experiments have shown that proteins clump together to form microscopic droplets (coacervates and microspheres)

• Coacervates and microspheres bear a resemblance to living cells.

Coacervates and Microspheres

a) All are set off from the environment by a membrane-like

boundary.

b) All can take up certain substances from their surroundings.

c) Certain chemical reactions can take place more easily inside these structures than they can in water.

d) Coacervates can grow and microspheres can bud.

• **DNA has been enclosed in membranes in the lab.

• This was a major step in the development of life because once DNA was separated from the environment by some kind of boundary, it would be protected and might be able to carry out the precise reactions of replication.

4. Evolution and Growth, Metabolism and Reproduction

• As lifelike as coacervates and microspheres appear, they lack the complexity of living things.

• They can neither maintain stable growth, nor reproduce. They also cannot obtain energy from substances in the environment. But over time, these capabilities may have developed. So far, no experiments account for the assembling of biomolecules into a living, replicating cell.

• In summary, evidence suggests that sometime between 4.6 and 3.5 billion years ago, life arose on earth, generated from non-living matter. Such spontaneous generation could not occur on earth today. The atmosphere of the young earth lacked oxygen gas which would have destroyed organic compounds by the chemical process called oxidation. Thus, the unique circumstances under which life spontaneously arose are no longer present on earth

• http://www.youtube.com/watch?v=v8nYTJf62sE