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CH 25 ~ HISTORY OF LIFE ON EARTH
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The Origin of Life
1st fossil evidence 3.5 BYA (Earth ~4.6 BY old)
4 stages 1 – abiotic synthesis of
organic molecules 2 – formation of
macromolecules 3 – formation of
protobionts 4 – formation of self-
replicating molecules
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Experimental evidence for the origin of life: Stanley Miller
Heated water (H2O), methane (CH4), ammonia (NH3), hydrogen (H2), and electrical charge
Amino acids were produced
Others determined RNA may have been the first macromolecule with enzyme activity
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Follow-up:
Which gas was least abundant in Earth’s early atmosphere, prior to 2 BYA? Oxygen Carbon dioxide Methane Water vapor Ammonia
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Protobionts
Molecules derived abiotically that are surrounded by a crude membrane
2 key traits: Accurate
reproduction Metabolism
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Origin of Unicellular Prokaryotes: 3.5-3.9 BYA (3:00)
Stromatolite: layered rocks formed by prokaryotes that bind sediment films together
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Origin of Eukaryotes: 2.1 BYA (7:00)
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Origin of Multicellularity: 1.2 BYA (8:00)
Confined to only a few areas due to several Ice Ages
Probably originated through cooperation of cells that each adopted specialized tasks
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Follow-up:
If natural selection in some environment favored the production of daughter cells that were genetically different from mother cells, one should expect selection for:
I – polynucleotide polymerases with low mismatch error rates
II – polynucleotide polymerases without proofreading capability
III - polynucleotide polymerases with proofreading capability
IV - polynucleotide polymerases with high mismatch error rates
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Cambrian Explosion: 535 MYA (10:00)
Extensive diversification of animal kingdom
Occurrence of predation features Claws, claspers defense – spines,
body armor
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Colonization of land: 500 MYA (10:20)
Fungi, plants, & animals move onto land
Associated with critical adaptations to terrestrial life
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Appearance of Homo sapiens: 195,000 YA (11:59 and 59 sec)
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Factors affecting evolution of species, I
Continental drift
Important in biogeography and climate changes
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Mass extinctions: Permean, 251
MYA Cretaceous, 65
MYA
Factors affecting evolution of species, II
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Adaptive Radiation
Periods of evolutionary change in which species are adapting to new ecological roles
Factors affecting evolution of species, III
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Slight genetic differences can produce major morphological differences in species
HOMEOTIC GENES
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Evolution is NOT goal-oriented
It all comes down to two things: survival and
reproduction
Exaptation: use of existing structures for new purposes
Paedomorphosis: using juvenile structures in adult organisms