Transcript The History of Life

The History of Life
Chapter 17
Pgs. 417-420; 435-440
17-1 The Fossil Record
• Palentologists: Scientists who study
fossils and infer what past life was like
• The Fossil Record: Shows that:
– Most organisms that ever lived on earth are
now extinct
– Modern organisms have unicellular (singlecelled) ancestors
– Fossils occur in a particular order with older
fossils in older rocks
17-1The Fossil Record
• Most fossils form in sedimentary rock
• Examples of fossils include:
– Eggs
– Footprints
– Body Parts
• When rock erodes from wind, rain and
shifting mountain ranges, older fossils can
be exposed which can then be studied
17-1 Fossils- Relative Dating
• Paleontologists use two techniques to
determine the age of fossils:
– Relative Dating
– Radioactive Dating
• Relative Dating:
– The age of a fossil is determined by comparing its
placement with fossils in other layers of rock
– Scientists can use index fossils to compare the
relative ages of fossils
– Allows paleontologists to estimate fossil’s age
compared to other fossils
17-1 Fossil Dating
• Radioactive Dating: Uses radioactive
decay to assign time ranges to rocks
– Uses half-life toe determine the length of time
required for ½ of the radioactive atoms in a
sample to decay
– Scientists calculate the age of a fossil by the
amount of remaining radioactive isotopes it
contains
17-1 Geologic Time Scale
• Geologic Time Scale: Scientists divisions
of the geologic time scale to represent
evolutionary time
– Studied rock layers and index fossils
worldwide and put them in order according to
relative age
– Precambrian Time covers about 88% of
Earth’s history
– After Precambrian Time the basic division
are eras and Periods
17-1 Geologic Time Scale
• Eras: There are 3 eras between the
Precambrian Era and the present:
– Paleozoic Era (500-250 million years ago)
– Mesozoic Era (250-65 million years ago)
– Cenozoic Era ( Earth’s most recent period: 65
million years ago-present)
• Periods: Each of the 3 eras are subdivided into
periods (pg.421 fig. 17-5)
– Earths most recent period is the Quaternary
17-2 Earth’s Early History
• The Formation of the Earth occurred nearly 4.6 billion
years ago:
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Early atmosphere contained poisonous gasses
Earth was struck by objects that generated heat and melted it
Earth cooled enough for rocks to form 4 billion years ago
Volcanic Activity began and made the Earth very hot
Comets and asteroids bombarded its surface
• Oceans did not exist until 3.8 billion years ago,
because the Earth was too hot and water remained a
gas
17-2 The Puzzle of Life’s Origin
• One necessary condition for the presence
of the first life on Earth was the presence
of liquid water
– Microspheres: 1st molecules that had some
characteristics of living systems
• Had permeable membranes, simple energy
systems
• Were similar to modern-day bacteria
17-2 Origin of Eukaryotic Cells
• Eukaryotic Cells: Cells that have a nucleus
– Original prokaryotic cells began developing cell
membranes
– Other prokaryotic cells invaded and began living in
the original prokaryotic cells
– These cells developed a symbiotic relationship with
one another
• Endosymbiotic Theory: Eukaryotic cells
developed from a symbiosis of several different
prokaryotic organisms
17-2 Origin of Eukaryotic Cells
• The Endosymbiotic Theory gained support
in the 1960’s by looking at chloroplasts
and mitochondira. Lynn Margulis of Boston
University made the following
observations:
– Mitochondrial DNA and chloroplast DNA
resemble bacterial (prokaryotic) RNA
– Their ribosomes resemble the ribosomes of
bacteria
– Like bacteria, they reproduce by mitosis
17-4 Patterns of Evolution
• Macroevolution:Large-scale evolutionary
patterns and processes that occur over long
periods of time. There are six of these:
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Extinction
Adaptive Radiation
Convergent Evolution
Coevolution
Punctuated Equilibrium
Changes in Developmental Genes
17-4 Patterns of Evolution
• Extinction: More than 99% of all species
that have ever lived are now extinct.
– There are several hypotheses to explain this
• EX: large asteroids hitting earth wiped out the
dinosaurs, errupting volcanoes and the continents
moving
– Each time one species became extinct it
opened up habitats for new species to
develop which cleared the way for evolution to
continue
17-4 Patterns of Evolution
• Adaptive Radiation: A single species that
has evolved into several different forms
that live in different ways
– EX: Darwin’s finches evolved into more than a
dozen different species from one original
species, Dinosaurs evolved at the same time
as 1st mammals, but eventually ruled the earth
until extinction
17-4 Patterns of Evolution
• Convergent Evolution: The process by
which unrelated organisms come to
resemble one another because they live in
similar environments with similar
environmental demands
– EX: Aquatic birds & swimming mammals like
Sharks, dolphins, seals and penguins all live
in water environments and have streamlined
bodies
17-4 Patterns of Evolution
• Coevolution: The process by which two
species evolve in response to one another
over time.
– An evolutionary change in one organism may
be followed by a change in another organism
• EX: A flower can reproduce only if it attracts a
specific type of pollinator
17-4 Patterns of Evolution
• Punctuated Equilibrium: Long stable
periods of evolutionary equilibrium
interrupted by brief periods of more rapid
change or evolution
– Can occur because:
• Small population becomes isolated from the main
part of the population
• Small group of organisms migrates to a new
environment- EX: Darwin’s finches