Chapter 17: The History of Life
Section 17-1: The Fossil Record
I. Interpreting fossil Evidence
A. Paleontologists are scientists who collect
and study fossils.
B. Age of fossils is determined using two
techniques:
1. Relative Dating:
2. Radioactive Dating
C. Relative Dating
1. Comparing a fossils placement
with fossils in other layers
of rock.
2. Oldest layers on the bottom,
recent layers on top.
D. Radioactive Dating
1. Some elements found in rocks are radioactive.
2. Radioactive elements break down, into non
radioactive elements at a steady rate.
3. A half life is the length of time required for half
of the radioactive atoms in a sample to decay.
4. The age of a fossil is calculated
based on the amount of
remaining radioactive
isotopes it contains.
Q. The half-life of Carbon-14 is 5,730 years. How much
of the original C-14 in an organism would remain in a
fossil that is 11,460 years old? _____________
Q. The half-life of the fictitious radioactive element X is
5,420 years.
• How old is a fossil that has 1/8th the original amount of the
element? _____________________________years old
• If I start out with 30 grams of element X, how much will I
have after 3 half-lives? _____________________grams
• If a fossil is found that has 5 grams of element X in it and I
know that it originally had 40 grams in it, how old is that
fossil? ___________________________________ years old
II. Origin of Eukaryotic Cells (with nuclei)
A. The prokaryotic cells began evolving internal cell
membranes. The result was the ancestor of
eukaryotic cells.
B. According to endosymbiotic theory some
prokaryotes entered this ancestral eukaryote &
began living inside the larger cell. Over time, a
symbiotic relationship evolved.
C. The prokaryotes that had an ability to use oxygen to
generate energy-rich molecules of ATP, evolved into
the mitochondria.
D. The prokaryotes that carried out photosynthesis
evolved into the chloroplasts.
Endosymbiotic Theory
Section 17-4: Patterns of Evolution
Macroevolution - large-scale evolutionary patterns
& processes that occur over long periods of time.
A. Mass extinction
1. Huge numbers of species along with ecological
systems disappear
2. Disrupts energy flow, and food webs collapse.
3. Survivors are left with an open habitat = burst of
evolution = many new species
B. Adaptive radiation
1. A single species or a small group of species
evolved, through natural selection into diverse
forms that live in different ways.
2. Example: Darwin’s Finches
3. The first dinosaurs and the earliest mammals
evolved at the same time.
• Dinosaurs & ancient reptiles, underwent an
adaptive radiation first & “ruled” Earth for about
150 million years
• During that time, mammals remained small &
relatively scarce.
• The disappearance of the dinosaurs cleared the
way for the great adaptive radiation of
mammals.
Adaptive Radiation of Mammals
C. Convergent evolution - unrelated organisms
resemble one another.
1. The organisms undergo adaptive radiation in
different places or at different times but in
similar ecological environments/climate.
2. Natural selection molds different body
structures, and they look similar & function in
the same way.
•
•
similar shapes of sharks and dolphins (streamlined
bodies with parts that work like paddles
structures such as a dolphin's flukes & a fish's tail fin
(look & function similarly, but are made up of parts
that do not share a common evolutionary history, are
called analogous structures).
D. Coevolution - two species evolve in response
to changes in each other over time.
1. Organisms that are closely connected to one
another by ecological interactions evolve together.
•
flowering plants can reproduce only if the shape, color,
& odor of their flowers attract a specific type of
pollinator.
2. An evolutionary change in one organism may be
followed by a corresponding change in another
organism.
•
relationships between plants and plant-eating insects.
Some plants have evolved poisonous compounds that
prevent insects from feeding on them. Natural
selection in herbivorous insects began to favor any
variants that could alter, inactivate, or eliminate those
poisons.
E. Gradualism versus Punctuated equilibrium
1. According to Darwin, biological change is slow
and steady, known as gradualism.
2. According to Stephen Jay Gould, the long and
stable periods interrupted by brief periods of
more rapid change is called as Punctuated
Equilibrium.
3. Rapid evolution may occur when a small
population becomes isolated and evolve rapidly
or when a small group of organisms migrates to a
new environment.
F. Changes in developmental genes
1. The “master control genes,” called hox genes,
guide development of major body structures in
animals.
2. Changes in the expression of developmental
genes may explain how
evolution occurred.