Early Earth and the Origin of Life

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Chapter 26 Early Earth and the Origin of Life
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A.  Introduction to the history of
life               Figure 26.1 (p. 511) Some
major episodes in the history of life.  
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Figure 26.2 (p. 512) Clock analogy for some key
events in evolutionary history.
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1.  The origin of the earth was approximately 4.5
billion years ago.   2.  It took almost 500
million years for the crust to solidify.   3. 
The oldest fossils of microorganisms were
embedded in rocks in western Australia that are
3.5 billion years old.                        
a.  Prokaryotes dominated history from 3.5 to 2
billion years ago.                                
     - During this time, the first divergence
occurred à Bacteria and Archae                    
                 Figure 26.3 (p. 512) Early
and modern prokaryotes.
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          Other fossilized evidence of bacteria
are present ? Stromatolites are fossilized
bacterial mats.  Many fossils of prokaryotes are
found in layers that make up the prokaryotic
mats.   Figure 26.4 (p. 513) Bacterial mats and
stromatolites.
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            4.  Oxygen began accumulating in
the atmosphere about 2.7 billion years
ago.                         a.  Cyanobacteria
are photosynthetic prokaryotes that are still
present today à produced oxygen.   Figure 26.5
(p. 513) Banded iron formations are evidence of
the age of oxygenic photosynthesis
approximately 2 BYA in photo
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5.  The oldest eukaryotic fossils are
approximately 2 billion years old.                
         a.  Symbiotic community of prokaryotes
living within larger prokaryotes.         ?
Mitochondria and chloroplasts   6.  The oldest
fossils of multicellular organisms are about 1.2
billion years old. In the photo of fossilized
algae (Figure 26.6) note the presence of two
types of cells (photosynthetic and hold fast).
This is evidence of specialization of cells
functions, that are important for development of
multicellular organisms.
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            7.  The oldest animal fossils are
about 700 million years old.                      
   a.  Animal diversity exploded around 540
million years ago.                          
Figure 26.7 (p. 515) Fossilized animal embryos
from Chinese sediments 570 million years ago.
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               Figure 26.8 (p. 515) The
Cambrian radiation of animals.             8. 
Plants, fungi, and animals began colonizing land
about 500 million years ago.                      
   a.  First plants transformed the
landscape                         b.  Then
animals were able to take advantage of new
niches                                     ?
Mammals evolved 50 to 60 million years ago.
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B.  The origin of life 1.  First cells may have
originated by chemical evolution involving 4
steps                         a.  Abiotic
(Non-biological) synthesis of small organic
molecules (monomers) ? C H organic
molecule   b.  Monomers joined together to form
polymers (proteins, nucleic acids)   c.  Origin
of self-replicating molecules (inheritance of
traits) ? proteins and polynucleic acids   d. 
Packaging of these organic molecules into
protobionts. ? Aggregates of abiotically produced
molecules that maintain an internal chemical
environment and exhibit some of the properties
associated with life (i.e. metabolism,
excitability).
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2.  Evidence that supports the four-stage
hypothesis for the origin of life                 
        a.  Oparin and Haldane in the 1920s ?
Abiotic synthesis of organic molecules is
testable in the laboratory   Hypothesis 
Conditions on primitive earth favored chemical
reactions that synthesized organic compounds from
inorganic precursors. These conditions were
different from what is now present and
include   - Reducing environment (no oxygen, but
instead H2O, CH4, and H2) lots of free
electrons that could be used to reduce carbon and
produce organic molecules.                        
- Energy from lots of lightning, UV radiation
(no O2 to block UV rays from the sun) and
volcanic activity (heat).
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b.  Miller and Urey in 1953                       
              i. Tested the Oparin-Haldane
hypothesis by creating conditions in which there
was an   - Atmosphere above warmed sea water that
contained H20, H2, CH4, and NH3 and   -
Electrodes that simulated lightning.   - From
this setup, they obtained organic compounds such
as amino acids that were collected in cooled
water.   Figure 26.10 (p. 518) The Miller-Urey
experiment.
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What they discovered was basically that organic
molecules could be created out of inorganic
molecules. Why dont we see this happening in
todays world ? Any organic molecules that are
now formed would be used up by living
organisms. If microorganisms were created from
these organic molecules in the early earths
water bodies, this would have been an example of
spontaneous creation! For much of history, man
believed that living organisms could be created
spontaneously from non-living material (e.g.
flies from dead meat, geese from barnacles,
etc.) This idea was refuted by Louis Pasteur in
the 1860s.
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c.  Louis Pasteur in the 1860s (Figure 26.9 (p.
517))                                     i. 
Tested whether microorganisms emerge by
spontaneous generation or by reproduction of
existing microorganisms.   - Microorganisms grew
in open containers of sterilized broth.  
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• However, microorganisms did not grow in closed
  containers of sterilized broth.
• Critics suggested that the life-giving force that
  was left over from the days of creation could not
  reach the broth through the sealed flask. Thus,
  life could not be created.

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• So Pasteur revised his experiment, using an open
  swan-neck flask. When he did this, he found
  that
• - Microorganisms did not grow in open swan-neck
  flasks filled with sterilized broth.
• If he then, broke the neck of the flask, he found
  that
• - Microorganisms grew in open flasks with broken
  necks.
• This meant that it must be that microorganisms
  entered the broth after the neck was broken this
  successfully
• Overturned the idea of spontaneous generation.
• ? As far as we know, all life today arises by
  reproduction.

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3.  RNA was probably the first hereditary
material a.  Today, genetic information is
usually stored as DNA, but some organisms such as
viruses use RNA to store info  
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4.  The precursors of early life are known as
Protobionts. a.  Protobionts form spontaneously
in lab experiments from mixtures of organic
molecules (Figure 26.12 (p. 520)). b.  They
contain RNA that codes for metabolic proteins.
These protobionts absorb food and the proteins
catalyze it to make energy which can be used for
growth and division to daughter cells. c. 
Natural selection would favor protobionts that
grow and replicate. When the organic molecules
in the earths water bodies were gone, the
protobionts would evolve to either obtain
energy by photosynthesis or predation. ? It would
only take the creation and evolution of one (1)
protobiont to give rise to the all the different
organisms we see today.
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This first or perhaps few protobionts gave rise
to all the diverse life now on the planet. Need
to remember the classification in order to
understand the phylogeny of life C.  Major
lineages of life             1.  At first, two
kingdoms were recognized à Plants and
Animals.               2.  In 1969, Robert
Whittaker developed a five-kingdom system à
Plants, Fungi, Animals, Protists, and Prokaryotes
(Monera).   Figure 26.15 (p. 522) Whittakers
five-kingdom system.
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            3.  The process of classifying
organisms is on-going and changing as new
information is being discovered. From this early
classification, we now have something that is
more complex ?   Figure 26.16 (p. 523) Our
changing view of biological diversity.
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