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Chapter 17
The History of Life
Interpreting Fossil Evidence
• Fossils have been
hidden in layers of
rocks for millions of
years
• Mostly found in
sedimentary rock
– Can be exposed due
to
• shifting earth layers
• Erosion from wind,
rain, and running
water
Relative Dating
• Order of appearance
– Age of fossil is determined
by comparing its
Younger
placement with that of
fossils in other layers
• Not precise, but allows
paleontologists to
estimate fossils age by
comparing with other
fossils
Older
Radioactive Dating
• Radioactive elements decay
at a constant rate
– Measured in units called half
life
– Half life = length of time
required for half of radioactive
atoms in sample to decay
• Use radioactive decay to
assign absolute ages to
rocks
• Scientists calculate age of a
sample based on amount of
remaining radioactive
isotopes it contains
How did life begin?
• Miller/Urey experiment
– 1950’s
– Tried to simulate conditions on
early earth in lab setting
• Filled flask with..
– Hydrogen, methane, ammonia, and
water
» Represented atmosphere
• Passed electric sparks though
mixture to simulate lightening
• WHAT DO YOU THINK
HAPPENED?
Miller/Urey continued….
• Over a few days…
– Several amino acids
formed!
• Building blocks of proteins
• Suggested how mixtures
of organic compounds
necessary for life could
have arisen from simpler
compounds present on
primitive Earth.
Tuesday April 23rd
• Which process is more accurate?
–Carbon dating or
–Relative dating
Patterns of Evolution
• Macroevolution
– Large scale evolutionary patterns/processes
that occur over long periods of time
Extinction
• More than 99% of
all species ever lived
are now extinct
• Mass extinctions
have wiped out
entire ecosystems
• Can be caused by
– Ice ages
– Meteorite
– Over time, just
happens
Adaptive Radiation
• Single species or
small groups of
species evolve
through natural
selection into
diverse forms that
live in different
ways.
– Ex. Darwin’s finches
• More than a dozen
evolved from single
species
Convergent evolution
• Adaptive radiation can
have “side effects”
• Convergent evolution
– Process by which
unrelated organisms
come to resemble one
another
• Swimming animals
–Sharks, dolphins,
penguins
Coevolution
• Process by which 2
species evolve in
response to
changes in each
other over time
Punctuated Equilibrium
• Describes pattern of long,
stable periods interrupted
by brief periods of more
rapid change
– Occur when…
• Small populations become
isolated from main population
• Small group migrates to new
environment
– Suggested that new species
are produced by periods of
rapid change.
• Controversial among
biologists
Developmental genes
and Body Plans
• Developmental genes
– Some determine which
parts of embryo become
front, rear, top, or
bottom
– Some determine size
and shape of legs or
wings
• Changes in expression of
developmental genes may
explain how differences
evolved in animals.
Endosymbiotic theory
• Eukaryotic cells arose from living
communities formed by prokaryotic
organisms
GET IN MY BELLY!
Prokaryotic cell
Poor, helpless little victim, about to become engulfed!
Warm UP – Nov. 21st
• Describe convergent evolution