2. Deep Time
• The Earth formed as a hot mass of molten rock
about 4.6 billion years ago (BYA)
• The first 700 million years of Earth’s history is
called the Hadean eon
– No rocks remain from Hadean Earth (melted)
– Hadean Earth was pummeled by asteroids, which
could potentially vaporize entire oceans
– Early atmosphere had high CO2 levels
– As CO2 levels dropped, temperatures shifted from
2000°C to -200°C; ocean froze
2
4. • Continents moved over geological time
– Earth’s crust formed rigid slabs of rock called
plates
• Under continents and oceans
• Two supercontinents formed
– Rodinia (all continents)
– Gondwana (all current Southern Hemisphere
continents)
– Pangea (formed from Gondwana)
4
5. • Evidence of life first appears in the Archean
eon fossils
– prokaryotes
• Proterozoic eon followed
– oxygen appeared in atmosphere
– eukaryotes and multicellular organisms
appeared
– Rodinia broke up
Hadean+Archean+Proterozoic = “PreCambrian Time”
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7. The past can be reconstructed
from the fossil record
• Fossils are the preserved remains of
once-living organisms
• Rock fossils are created when three
events occur
– Organism buried in sediment
– Calcium in bone or other hard tissue
mineralizes
– Surrounding sediment hardens to form rock
• Process of fossilization is rare event
7
8. Determining the age of fossils
• Fossils are the preserved remains of once-living organisms
• Rock fossils are created when three events occur
– Organism buried in sediment
– Calcium in bone or other hard tissue mineralizes
– Surrounding sediment hardens to form rock
• Process of fossilization is rare event
• Relative age: age of fossils is estimated by
position of the fossil in the sediment
• Absolute age: age of fossils is estimated
by rates of radioactive decay
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9. Absolute Age
• Isotopes transform at precisely known
rates into nonradioactive forms
• The rate of decay is known as an isotope’s
half-life
– Amount of time needed for one-half of the
original amount to be transformed
• Types of Isotopes used in aging fossils
– Potassium isotopes: 1.25 billion year half-life
– Carbon isotopes: 5700 billion year half-life
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11. Organic molecules may have
originated on early Earth
• Few geochemists agree on exact
composition of early atmosphere
– Popular view of early atmosphere
• Carbon dioxide (CO2)
• Nitrogen gas (N2)
• Water vapor (H2O)
• Hydrogen gas (H2)
• Other sulfur, nitrogen, and carbon compounds
– Atmosphere lacked oxygen gas (O2)
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13. 13
The Miller–Urey Experiment
Water vapor
Samples tested
for analysis
Electrodes
discharge
sparks
(lightning
simulation)
Reducing atmosphere
mixture (H2O, N2, NH3,
CO2, CO, CH4, H2)
Condenser
Cool water
Condensed liquid with
complex molecules
Many cycles
during one
week
Heated water
(“ocean”)
Heat source
Small organic molecules
including amino acids
Boiler
In 1953, Miller and Urey did an experiment that reproduced early atmosphere
• Atmosphere placed over liquid water
• Temperature below 100ºC
• Simulate lightning with sparks
16. • Living things are selective in the carbon
isotopes used
– Living things incorporate carbon-12
– Higher level of carbon-12 than nonliving
things
• Isotopic analysis of carbon-12 in fossils
suggests that carbon fixation (ie
photosynthesis?) was active as much as
3.8 BYA
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17. Earth’s Changing System
• Climate (temperature and water
availability) and atmosphere are among
the many factors that affect survival
• Dramatic shifts in all these factors led to
mass extinctions influencing the course of
evolution
– Earth has been cooling since its formation
– Extreme drops in temperature resulted in glacial ice
covering Earth
• Continental motion affected evolution
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24. • Eukaryotes have
compartmentalization
– an endomembrane system
(from infolded plasma
membranes)
– mitochondria and
chloroplasts are derived
from engulfed purple-sulfer
bacteria and
cyanobacteria
(“endosymbiosis”)
24
26. Multicellularity leads to cell specialization
• A unicellular body plan is tremendously
successful
– Unicellular prokaryotes and eukaryotes
constitute about half of the biomass on Earth
– Single cell has limits with cell specialization
• Multicellularity allowed organisms to deal with
environment in novel ways through
differentiation/specialization
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28. Sexual reproduction increases
genetic diversity
• First eukaryotes were probably haploid
• Diploids seem to have arisen on several
separate occasions, via fusion of haploid
cells, followed by mitotic divisions.
• Sexual reproduction allows greater genetic
diversity (meiosis and fusion of gametes)
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29. Rapid diversification occurred
during the Cambrian period
• Cambrian period marks the beginning of
the Phanerozoic eon
• The “Cambrian explosion” (or “Cambrian
radiation”) was confined to ocean
– First multicellular animals appeared 50 million
years following Cambrian radiation
29
31. Major innovations allowed
for the move onto land
• Plants and then animals colonized
terrestrial environments after Cambrian
radiation (land plants, then arthropods,
then tetrapods)
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32. Key Eukaryotic Characteristics
• Compartmentalization
– Allows for increased subcellular specialization
– Nuclear membrane allows for additional levels
of control of transcription and translation
• Multicellularity
– Allows for differentiation of cells into tissues
• Sexual reproduction
– Allows for greater genetic diversity
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33. Naming diverse organisms
is essential in biology
• Emphasis is on constructing evolutionary
hypotheses to explain the relatedness of
species
• Organisms are given genus and species
names (binomial system)
• Related organisms are grouped into
clusters
– Family, order, class, phylum, kingdom
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