Transcript The History of Life

The History of Life & the Origin of Species
Georgia Performance Standards:
SB5a: Trace the history of the theory of evolution.
SB5 c: Explain how fossil and biochemical evidence
support the theory of evolution.
Essential Questions:
1. Why are there species alive now that were not found
in the past fossil record?
2. Why is important to understand evolutionary theory?
3. How does fossil and biochemical evidence support
the evolutionary theory?
14–1 The Fossil Record
• You can study life’s history by examining
fossils.
• The fossil record provides evidence
about the history of life on Earth.
– It also shows how different groups of
organisms have changed over time.
– Paleontologists are scientists who collect
and study fossils.
Fossils can show:
– That life on Earth has changed over time.
– What past life forms were like and if they are extinct
(the species died out)
– The structure of the organisms
– What they ate
– What ate them
– The environment in which they lived.
How Fossils Form
• Either the remains of the organism or
some trace of its presence must be
preserved.
– Most fossils form in sedimentary rock
– The quality of fossil preservation varies.
Formation of a Fossil
Section 17-1
Water carries small
rock particles to
lakes and seas.
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Dead organisms are
buried by layers of
sediment, which
forms new rock.
The preserved
remains may later
be discovered and
studied.
Interpreting Fossil Evidence
• Relative dating, the age of a
fossil is determined by
comparing its placement
with that of fossils in other
layers of rock
– use index fossils to
compare the relative ages
of fossils.
– Relative dating allows
paleontologists to
estimate a fossil’s age
compared with that of
other fossils.
Interpreting Fossil Evidence
• Radioactive dating is the use
of half-lives to determine the
age of a sample.
– A half-life is the length of
time required for half of the
radioactive atoms in a
sample to decay.
• In radioactive dating,
scientists calculate the age
of a sample based on the
amount of remaining
radioactive isotopes it
contains.
Compare/Contrast Table
Section 17-1
Comparing Relative and Absolute Dating of Fossils
Relative Dating
Can determine
Is performed by
Drawbacks
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Age of fossil with respect to
another rock or fossil (that is,
older or younger)
(Absolute Dating)
Radioactive Dating
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
Geologic Time Scale
• Paleontologists use divisions
of the geologic time scale to
represent evolutionary time.
• After Precambrian Time, the basic
divisions of the geologic time scale are
eras and periods.
Geologic Time Scale
• Geologists divide the
time between the
Precambrian and the
present into three
eras.
– Paleozoic Era
– Mesozoic Era
– Cenozoic Era
• Eras are subdivided
into periods, which
range in length from
tens of millions of
years to less than two
million years.
Geologic Time Scale with Key Events
Section 17-3
Era
Cenozoic
Mesozoic
Paleozoic
Precambrian
Time
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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
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14.1 Fossil Evidence of Change
 Plate tectonics describes the movement of
several large plates that make up the surface of
Earth.
 These plates, some of which contain continents,
move atop a partially molten layer of rock
underneath them.
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Concept Map
Section 17-2
Evolution of Life
Early Earth was hot; atmosphere contained poisonous gases.
Earth cooled and oceans condensed.
Simple organic molecules may have formed in the oceans..
Small sequences of RNA may have formed and replicated.
First prokaryotes may have formed when RNA or DNA was enclosed in microspheres.
Later prokaryotes were photosynthetic and produced oxygen.
An oxygenated atmosphere capped by the ozone layer protected Earth.
First eukaryotes may have been communities of prokaryotes.
Multicellular eukaryotes evolved.
Sexual reproduction increased genetic variability, hastening evolution.
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14.2 The Origin of Life
Origins: Early Ideas
 Spontaneous generation is the idea that life arises
from nonlife.
 Francesco Redi, an Italian scientist, tested the idea
that flies arose spontaneously from rotting meat.
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14.2 The Origin of Life
 The theory of biogenesis states that only living
organisms can produce other living organisms.
 Louis Pasteur designed an experiment to show
that biogenesis was true even for
microorganisms.
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14.2 The Origin of Life
Origins: Modern Ideas
 Simple organic molecule formation
 The primordial soup hypothesis was an
early hypothesis about the origin of life.
 Organic molecules could have been
synthesized from simple reactions.
 UV light from the Sun and electric
discharge in lightning might have been
the primary energy sources.
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14.2 The Origin of Life
 Stanley Miller and
Harold Urey were the
first to show that
simple organic
molecules could be
made from inorganic
compounds.
 Later, scientists found
that hydrogen cyanide
could be formed from
even simpler molecules
in simulated early Earth
environments.
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14.2 The Origin of Life
Making Proteins
 Life requires proteins.
 One possible mechanism for the formation of
proteins would be if amino acids were bound to a
clay particle.
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14.2 The Origin of Life
Genetic Code
 Some RNA sequences appear to have
changed very little through time.
 Many biologists consider RNA to have been
life’s first coding system.
 Other researchers have proposed that clay
crystals could have provided an initial
template for RNA replication.
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14.2 The Origin of Life
Cellular Evolution
 Scientists hypothesize that the first cells
were prokaryotes.
 Many scientists think that modern
prokaryotes called archaea are the closest
relatives of Earth’s first cells.
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14.2 The Origin of Life
Photosynthesizing Prokaryotes
 Archaea are autotrophic.
 They do not obtain their energy from the Sun.
 Archaea also do not need or produce oxygen.
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14.2 The Origin of Life
 Many scientists think that photosynthesizing
prokaryotes evolved not long after the
archaea.
 Prokaryotes, called cyanobacteria, have been
found in rocks as old as 3.5 billion years.
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14.2 The Origin of Life
The Endosymbiont Theory
 The ancestors of eukaryotic cells lived in
association with prokaryotic cells.
 The relationship between the cells
became mutually beneficial, and the
prokaryotic symbionts became
organelles in eukaryotic cells.
 This theory explains the origin of
chloroplasts and mitochondria.
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14.2 The Origin of Life
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Checkpoint Questions:
• What can be learned from the fossil record?
• Which type of dating provides an absolute age
for a given fossil? Describe how this is done.
• How are eras and periods related?
• Many more fossils have been found since
Darwin’s day, allowing several gaps in the fossil
record to be filled. How might this information
make relative dating more accurate?