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?*
-
-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 nonliving 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