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The Fossil Record and Geologic Time Scale
19-1 The Fossil Record
The Fossil Record and Geologic Time Scale
Chapter 19.1 Essential Questions
• What do fossils reveal about ancient life?
• How do we date events in Earth’s history?
• How was the geologic time scale
established, and what are its major
divisions?
• How have our planet’s environment and
living things affected each other to shape
the history of life on Earth?
The Fossil Record and Geologic Time Scale
Fossils and Ancient Life
– Fossil record:
Provides evidence about the history of life on Earth.
Shows how organisms have changed over time.
– More than 99% of all species that have ever lived
on Earth are extinct.
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The Fossil Record and Geologic Time Scale
• Specific conditions are needed for fossilization.
• Small % of living things became fossils.
• Many did not leave a trace
• fossil record is incomplete.
The Fossil Record and Geologic Time Scale
Fossils can form in several ways.
• Permineralization occurs when minerals
carried by water are deposited around a hard
structure.
• A natural cast forms when flowing water
removes all of the original tissue, leaving an
impression.
The Fossil Record and Geologic Time Scale
• Trace fossils record the activity of an
organism.
The Fossil Record and Geologic Time Scale
Interpreting Fossil Evidence: Relative Dating
The Age of fossils can be
determined by:
 Relative dating and/or
 Radiometric dating
Relative dating:
 Compare the placement
of fossils in layers of rock
Index fossils!
The Fossil Record and Geologic Time Scale
• Radiometric dating uses decay of unstable isotopes.
– Isotopes are atoms of an element that differ in their
number of neutrons.
– Radioactive isotopes decay into stable isotopes at a
rate that can be measured.
neutrons
protrons
The Fossil Record and Geologic Time Scale
• Radiometric Dating
– A half-life (t1/2) is the amount of time it takes for
half of the isotope to decay.
The Fossil Record and Geologic Time Scale
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The Fossil Record and Geologic Time Scale
The Fossil Record and Geologic Time Scale
Evidence of Continental Drift
The Fossil Record and Geologic Time Scale
19-2 Patterns and
Processes of Evolution
The Fossil Record and Geologic Time Scale
Chapter 19.2 Essential Questions
• What processes influence whether species and
clades survive or become extinct?
• How fast does evolution take place?
• What are 2 patterns of macroevolution?
• What evolutionary characteristics are typical of
coevolving species?
The Fossil Record and Geologic Time Scale
Speciation and Extinction
Macroevolution refers to largescale evolutionary patterns and
processes that occur over long
periods of time.
The Fossil Record and Geologic Time Scale
Macroevolution
Six important topics in
macroevolution are:
1. Extinction
2. Adaptive radiation
3. Convergent evolution
4. Coevolution
5. Punctuated equilibrium
6. Changes in developmental
genes (Hox Genes)
The Fossil Record and Geologic Time Scale
Extinction
• Background extinction: Slow and steady extinction
• Mass extinction: Drastic change causes many
species to become extinct in a short period of time.
The Fossil Record and Geologic Time Scale
Extinction
• What effects have mass
extinctions had on the history
of life?
• Mass extinctions have:
– Provided ecological
opportunities for organisms
that survive
– Resulted in bursts of
evolution that produced many
new species
The Fossil Record and Geologic Time Scale
The Fossil Record and Geologic Time Scale
Gradualism
• Darwin felt that evolution was slow and steady
The Fossil Record and Geologic Time Scale
Punctuated Equilibrium:
The Fossil Record and Geologic Time Scale
Reasons for rapid evolution
• Small population
– becomes isolated
– migrates to a new
environment
• Mass extinctions
allow species to fill
their niche
The Fossil Record and Geologic Time Scale
The Fossil Record and Geologic Time Scale
Macroevolution : Adaptive Radiation
• Adaptive radiation:
• Process by which a small group of species evolves into
several different forms.
The Fossil Record and Geologic Time Scale
Adaptive Radiation
• Two species can’t occupy the same niche
within an ecosystem
– i.e. can’t have large mammal carnivores and large reptile
carnivores…one is going to prevail
• If there is an opening within a system, due to
extinction, then another species will fill that
niche
– i.e. dinosaurs became extinct, so mammals filled the
niches left open
The Fossil Record and Geologic Time Scale
Macroevolution:
• Convergent evolution: The process by
which distantly related organisms come to
resemble one another, which results in
analogous structures.
The Fossil Record and Geologic Time Scale
• Sometimes organisms that are closely connected to
one another by ecological interactions evolve together.
• Coevolution: Process by which 2 species evolve in
response to changes in each other over time.
The Fossil Record and Geologic Time Scale
19-3 Earth’s Early History
The Fossil Record and Geologic Time Scale
Chapter 19.3 Essential Questions
• What do scientists hypothesize about early
Earth and the origin of life?
• What theory explains the origin of eukaryotic
cells?
• What is the evolutionary significance of sexual
reproduction?
The Fossil Record and Geologic Time Scale
The Mysteries of Life’s Origin
 Formation of Earth
• Cosmic debris collided
• Meteor strikes caused it to
melt
• Earth cooled 4.2 BYA
• Elements rearranged
themselves according to
density
– Most dense-core
– Moderately dense – crust
– Least dense - atmosphere
The Fossil Record and Geologic Time Scale
Miller-Urey Experiment
Attempted to demonstrate whether or not organic molecules could have been
produced before life was present.
After a week produced sugars and 21 amino acids!
The Fossil Record and Geologic Time Scale
Formation of Microspheres
• Protenoid microspheres:
bubbles given off from organic
molecules
– have many characteristics
of living cells
Semi-permeable membrane,
Able to store and release
energy
• First forms of life were
prokaryotic cells
– Over time they became
more and more advanced
(3.8 BYA)
The Fossil Record and Geologic Time Scale
Evolution of RNA and DNA
• RNA world hypothesis: RNA existed before DNA.
• Small sequences of RNA formed from simpler
molecules.
The Fossil Record and Geologic Time Scale
The Heterotroph Hypothesis
The 1st organisms on the Earth were:
• Anaerobic Heterotrophs
• First prokaryotes
• Simple archaen bacterial cells
• Photosynthetic prokaryotes
• aerobic prokaryotes, eukaryotes, multicellular organisms
The Fossil Record and Geologic Time Scale
Comparing Atmospheres
 Many scientists think Earth’s early atmosphere may have been
similar to the gases released by a volcano today.
The Fossil Record and Geologic Time Scale
Origin of Eukaryotic Cells
Endosymbiotic Theory:
Eukaryotic cell organelles
arose from prokaryotic
organisms
Specific Evidence
• Mitochondria and
chloroplasts:
– DNA similar to
bacterial DNA
– Similar ribosomes
– Reproduce by
binary fission
The Fossil Record and Geologic Time Scale
Endosymbiotic Theory
The Fossil Record and Geologic Time Scale
Sexual Reproduction and Multicellularity
• Once eukaryotic cells
arose they reproduced
sexually
– increasing genetic variation
and speeding up
evolutionary change.
• Multicellular organisms
arose
– a few hundred million
years after the evolution of
sexual reproduction.