Transcript The History of Life

The History of Life?
Chapter 12
Where did life come from?
• Many theories, ideas, and opinions exist
• NO ONE knows exactly
• Early idea:
Spontaneous Generation – nonliving
material can produce life
• First disproved in 1668 by Francesco
Redi (Italian Physician) – used decaying
meat in jars to show that flies produce flies
• See page 388 in textbook
Experimental Group
Control Group
One jar was
left uncovered.
The second jar
was covered.
Maggots
appeared on the
meat in the
open jar.
Redi concluded
that meat did
not produce
maggots.
• Though Redi had disproved spontaneous
generation of large organisms, many scientists
thought that microorganisms were so numerous
that they could arise spontaneously – from a
“vital force” in the air
• In mid-1800’s, Louis Pasteur designed an
experiment that disproved the spontaneous
generation of microorganims – see page 389
Figure 26.9 Pasteur and biogenesis of microorganisms (Layer 1)
Figure 26.9 Pasteur and biogenesis of microorganisms (Layer 2)
Figure 26.9 Pasteur and biogenesis of microorganisms (Layer 3)
Biogenesis
• “life comes from life”
• Result of Pasteur’s experiment
• Cornerstone of Biology
Biogenesis does NOT answer
origin of life…
• Again, no one knows for sure, but there are
several theories that have developed for HOW
life on Earth originated
2 developments must have preceeded life on
Earth:
1. simple organic molecules must have
formed
2. These simple organic molecules
organized into complex organic molecules –
carbs, lipids, proteins, nucleic acids
Alexander Oparin
• 1930’s
• Russian scientist
• Hypothesized that life began in the oceans
on the early Earth
• Suggested that energy from sun, lightning,
and Earth’s heat triggered chemical
reactions that formed organic molecules
• Rain washed these into the oceans –
“primordial soup”
• DID NOT DO ANY EXPERIMENTATION –
purely theoretical
Creating the potential for life
Stanley Miller and Harold Urey
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1953
American scientists
Tested Oparin’s hypothesis
Simulated conditions of early Earth in lab
Mixed water vapor with ammonia, methane, and
hydrogen gases
Sent in an electrical current (“lightning”)
Cooled the mixture, collected liquids
Found amino acids, sugars, and other small organic
molecules
See page 390
Figure 26.10 The Miller-Urey experiment
Taking it further…
• 1950’s – experiments showed that if amino acids are
heated without oxygen present, they link and form
proteins
• Can also form ATP and nucleic acids in a similar manner
• HOW FORMED FIRST CELLS?
• Sidney Fox – American biochemist
*demonstrated formation of protocells – large,
ordered structures enclosed by membranes that carry
out some life activities (growth and division)
See page 391 in textbook
*also called protobionts – not living, but show simple
characteristics of life
Endosymbiosis/
Gaia Theory
• 1960’s
• Proposed by American biologist, Lynn Margulis
• Possible explanation for eukaryotic cell
formation
• Proof: separate DNA and extra membranes
around mitochondria and Chloroplasts
Endosymbiosis – Evolution from
Bacteria
Eukaryotic –
chloroplasts
inside…
Eukaryotic –
mitochondria
inside…
• endosymbiosis animation