Chapter 17
The History
of Life
Fossil imprint
The Fossil Record
• Provides evidence
about the history of
life on Earth.
• It also shows how
different groups of
organisms, including
species, have
changed over time.
Relative vs. Absolute Dating
Comparing Relative and Absolute Dating of Fossils
Can determine
Is performed by
Drawbacks
Relative Dating
Absolute Dating
Age of fossil with respect to
another rock or fossil (that is,
older or younger)
Age of a fossil in years
Comparing depth of a fossil’s
source stratum to the position
of a reference fossil or rock
Determining the relative
amounts of a radioactive
isotope and nonradioactive
isotope in a specimen
Imprecision and limitations of
age data
Difficulty of radioassay
laboratory methods
Principle of Superposition
• In an undisturbed sequence of
sedimentary rocks, the oldest rocks are on
the bottom with the most recent on top.
How fossils are formed
Water carries small rock
particles to lakes and seas.
Dead organisms are buried
by layers of sediment, which
forms new rock.
The preserved remains
may later be discovered
and studied.
Geological Time Scale
• After the Precambrian Time, the time scale
is divided into eras, which are subdivided
into periods.
Era
Period
(millions of
Time years ago)
Quaternary
1.8–present
Tertiary
65–1.8
Cretaceous
145–65
Jurassic
208–145
Triassic
245–208
Era
(millions of
Period
Time years ago)
Permian
290 – 245
Carboniferous
360–290
Devonian
410–360
Silurian
440–410
Ordovician
505–440
Cambrian
544–505
Era
(millions of
Period
Time years ago)
Vendian
650–544
Geological Time Scale
• The major eras are Paleozoic, Mesozoic,
and Cenozoic.
Era
Period
(millions of
Time years ago)
Quaternary
1.8–present
Tertiary
65–1.8
Cretaceous
145–65
Jurassic
208–145
Triassic
245–208
Era
(millions of
Period
Time years ago)
Permian
290 – 245
Carboniferous
360–290
Devonian
410–360
Silurian
440–410
Ordovician
505–440
Cambrian
544–505
Era
(millions of
Period
Time years ago)
Vendian
650–544
Geologic Time Scale
• Each period hosts significant evolutionary
changes to species diversity and
extinction.
Era
Period
(millions of
Time years ago)
Quaternary
1.8–present
Tertiary
65–1.8
Cretaceous
145–65
Jurassic
208–145
Triassic
245–208
Era
(millions of
Period
Time years ago)
Permian
290 – 245
Carboniferous
360–290
Devonian
410–360
Silurian
440–410
Ordovician
505–440
Cambrian
544–505
Era
(millions of
Period
Time years ago)
Vendian
650–544
Summary of major events
(pg. 429-34)
Era
Cenozoic
Mesozoic
Paleozoic
Precambrian
Time
Period
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Time
(millions of
years ago)
1.8–present
65–1.8
145–65
208–145
245–208
290–245
363–290
410–363
440–410
505–440
544–505
650–544
Key Events
Glaciations; mammals increased; humans
Mammals diversified; grasses
Aquatic reptiles diversified; flowering plants; mass extinction
Dinosaurs diversified; birds
Dinosaurs; small mammals; cone-bearing plants
Reptiles diversified; seed plants; mass extinction
Reptiles; winged insects diversified; coal swamps
Fishes diversified; land vertebrates (primitive amphibians)
Land plants; land animals (arthropods)
Aquatic arthropods; mollusks; vertebrates (jawless fishes)
Marine invertebrates diversified; most animal phyla evolved
Anaerobic, then photosynthetic prokaryotes; eukaryotes,
then multicellular life
Hypothesis of early Earth
• Very hot surface from
colliding meteorites
• Very hot planet core
from radioactive
materials
• Volcanoes spewing
lava and gases that
helped to form the
early atmosphere
Hypothesis of early Earth
• About 4.4 billion years ago, Earth might
have cooled enough for the water in its
atmosphere to condense.
• This might have led to millions of years of
rainstorms with lightning, enough rain to fill
depressions that became Earth’s oceans.
• The oldest rocks dated are 3.9 million
years old.
Fossils: evidence of an organism that
lived long ago that is preserved in
Earth’s rocks
• Paleontologists
estimate that
about 95%
species are
extinct from
life’s origins.
• Climate and
ancient
geography can
be determined
from fossils.
Types of Fossils
Formation
Fossils Types
A trace fossil
is any
indirect
A trace
fossil
is anyevidence
indirect evidence
Trace fossils
left by an animal and may include a
footprint, a trail, or a burrow.
When minerals in rocks fill a space
left by a decayed organism, they make
a replica, or cast, of the organism.
Casts
Molds
A mold forms
when
an organism
is
A mold
forms
when an organism
is
Petrified/
Permineralized
fossils
AmberPreserved or
frozen fossils
buried in sediment and then decays,
leaving an empty space.
Petrified-minerals sometimes penetrate
and replace the hard parts of an
organism. Permineralized-void spaces
in original organism infilled by
minerals.
At times, an entire organism was
quickly trapped in ice or tree sap that
hardened into amber.
What has been learned from
fossils
• several episodes of mass extinction that
fall between time divisions
– mass extinction: an event that occurs when
many organisms disappear from the fossil
record almost at once
• The geologic time scale begins with the
formation of Earth about 4.6 billion years
ago.
Precambrian – 87% of history
• Oldest fossils about 3.4 billion years old
resembling cyanobacteria stromatolites.
• Stromatolites still form today in Australia
from mats of cyanobacteria.
• The stromatolites are evidence of the
existence of photosynthetic organisms on
Earth during the Precambrian.
• Only prokaryotic life found in fossil record
End of Precambrian – 543 MYA
• multicellular eukaryotes,
such as sponges and
jelly-fishes, diversified
and filled the oceans
Paleozoic and Cambrian Period
• Paleozoic Era: more animals and plants
– Early: fishes, aquatic vertebrates, ferns
– Middle: amphibians
– Late: reptiles and mass extinction
– Cambrian Period: oceans teemed with many
types of animals, including worms, sea stars,
and unusual arthropods
Mesozoic - 248 MYA
• Triassic Period: mammals and dinosaurs
• Jurassic Period: dinosaurs and birds
• Cretaceous Period: more mammals,
flowering plants, but mass extinction of
dinosaurs 65 MYA
Continental drift
• Earth’s continents have moved during
Earth’s history and are still moving today
at a rate of about six centimeters per year.
• The theory for how the continents move is
called plate tectonics.
Geologic Time Scale video
Click on image to play video.
Miller-Urey experiment showed one possible
way for inorganic molecules to form organic
molecules.
Mixture of gases
simulating
atmospheres of
early Earth
Spark simulating
lightning storms
Condensation
chamber
Water
vapor
Cold
water
cools
chamber,
causing
droplets
to form
Liquid containing
amino acids and
other organic
compounds
How eukaryotic cells evolved
• Lynn Margulis proposed the endosymbiotic
theory.
Chloroplast
Aerobic
bacteria
Ancient Prokaryotes
Nuclear
envelope
evolving
Plants and
plantlike
protists
Photosynthetic
bacteria
Mitochondrion
Primitive Photosynthetic
Eukaryote
Ancient Anaerobic
Prokaryote
Primitive Aerobic
Eukaryote
Animals, fungi, and
non-plantlike protists
Endosymbiotic theory
• Heterotrophic bacteria have plasmids
(DNA loop) & simple ribosomes in their
cytoplasm
• Mitochondria have circular DNA &
bacteria-like ribosomes
• So…Eukaryotic cells may have engulfed
prokaryotic cells & by mutualism created
the “first mitochondria.”
• Autotrophic bacteria are Cyanobacteria
with chlorophyll
• So, Eukaryotic cells may have engulfed
prokaryotic cyanobacteria & by mutualism
created the “first chloroplast.”
• Heterotrophic symbiosis = symbiont
produces ATP, host uses ATP, host
protects symbiont
• Autotrophic symbiosis = symbiont
produces sugar, host uses sugar,
host protects symbiont
• Relationships may allow host to live longer
& reproduce more, thus over time creating
more complex eukaryotic cells
Evolution of life video
Click on image to play video.
Macroevolution
 Large-scale evolutionary patterns and
processes that occur over long periods of time.
 Includes 6 topics:
Extinction
Adaptive radiation
Convergent evolution
Divergent evolution
Punctuated equilibrium
Changes in developmental genes
Patterns of evolution
• Darwin believed that
organisms evolved
gradually.
• Niles Eldredge and
Stephen Jay Gould
believed punctuated
equilibrium is how
organisms evolved,
periods of rapid
evolution followed by
periods of stasis.
Adaptive Radiation
• Single species or small groups of species
evolved into diverse forms living in different
ways.
Convergent Evolution
• Adaptive radiation can produce unrelated
organisms that look similar due to similar
environments.
Coevolution
The process by which
two species evolve in
response to changes in
each, other over time.
http://ecology.botany.ufl.edu/ ecologyf02
• Example: “This butterfly
acquires a cardiac
glycoside from members
of the genus Asclepias.
Because of their milky
sap, these are commonly
referred to as milkweed
plants. The plants
produce this toxin as a
defense against
herbivory, but the
Monarch has the ability to
sequester the toxin in
fatty tissues so that it
makes the butterfly
unpalatable while not
poisoning the butterfly.”