Transcript The History of Life - Kentucky Department of Education

The History of Life
Early History of Earth
Early Earth was inhospitable!
It was probably very hot, volcanoes might have erupted
frequently spewing gases and lava
• These gases helped form Earth’s early atmosphere which
contained little oxygen but abundant carbon dioxide and
nitrogen
About 3.9 billion years ago, earth might have cooled enough
for water in the atmosphere to condense
• This would have led to millions of years of rainstorms,
enough to fill Earth’s oceans
 It is in the oceans that scientist propose that the first
organisms appeared between 3.9 and 3.5 billion years ago
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History in Rocks
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Scientist cannot be sure that earth formed in this
way. There is no direct evidence of the earliest
years of Earth’s history.
 The physical processes of Earth constantly
destroy and reform rock.
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The oldest rocks that have been found on earth
formed only about 3.9 billion years ago
Rocks are an important source of information
about the diversity of life that once existed on
the planet
Fossils – Clues to the Past
 The
millions of species that live today are
probably only a small fraction of all the
species that ever existed.
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About 99% of species are extinct – they no
longer live on Earth
– evidence of an organism that lived
long ago.
 Fossil
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Scientists use fossils to learn about ancient
species.
The Origin
of Life
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Francesco Redi’s experiment
(1668)
How do the results differ in the two
jars?
What might you conclude from
these results?
Louis Pasteur’s experiment –
finally disproved spontaneous
generation (mid 1800’s)
Which came first, the chicken or
the egg?
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Biologists have accepted the concepts of
biogenesis for more than 100 years
Biogenesis does not answer the question of how
life began on Earth
No one will ever know for certain how life began
on earth. We can only make hypotheses about
conditions on early Earth.
How does chemistry become life??
 Evolution
of complex molecules
Primordial Soup
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Step 1: simple organic molecules must
have formed (molecules that contain
carbon)
Step 2: Simple organic molecules must
have become organized into complex
organic molecules (proteins, carbohydrates,
and nucleic acids)
1930’s Oparin (Russian) – hypothesized
that life began in the oceans
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Energy from sun and lightning triggered
chemical reactions to produce small
organic molecules from substances in
the atmosphere
1953 Miller and Urey (American) –
replicated conditions in the lab and
produced amino acids, sugars, and other
molecules
The next step…

How did we get from simple organic
compounds to complex organic compounds?
 In the presence of heat, without oxygen,
amino acids link to from proteins. ATP is
produced in a similar way.
 Sidney Fox found that if you continued to heat
the complex organic compounds protocells
developed.
The Evolution of Cells
 The
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first true cells…
Prokaryotes that evolved from a protocell
Anaerobic (no oxygen present in atmosphere)
Food – organic molecules abundant in oceans
Autotrophs evolved to inhabit harsh conditions
(ie. Archaebacteria)
Endosymbiont Theory
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Eukaryotes probably evolved from prokaryote cells
Theory proposes that eukaryotes evolved through a symbiotic
relationship between prokaryotes
 Evidence:
• Chloroplast and cyanobacteria – resemble eachother
• mitochondria and bacteria – some look similar
• Chloroplast and mitochondria contain DNA that is similar to the DNA
in prokaryotes
• Today, some prokaryotes live in close association with eukaryotes
Life Today
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Could new life originate on Earth today?
 List the specific evidence that supports each
conclusion.
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Life comes from existing life
Life probably originated on Earth through the reaction
of chemicals in Earth’s atmosphere and their further
reaction on Earth’s surface
Cells probably evolved as the chemicals on early
Earth became more organized.