Transcript Notes 7-2 and 8-2

Notes 7-2 and 8-2
Evidence and fossils
Evidence of evolution
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Similar body structures
Patterns of early development
Molecular structure
Fossils
Homologous Structures
• The structure of the bones in a dolphin’s flipper, a
bird’s wing, and a dog’s leg is similar. Homologous
bones are shown in the same color.
•
Patterns of early development:
Can you tell the difference
between these embryos?
Which one is the human?
Human
Fish
Tortoise
Chicken
Salamander
Pig
Rabbit
Cow
What about now?
Which ones look most alike?
Human
Fish
Tortoise
Chicken
Salamander
Pig
Rabbit
Cow
How Do Fossils Form?
• Most fossils form when organisms that die
become buried in sediments.
Changes Over Time
• The fossils record
provides evidence
about the history of
life and past
environments on
Earth. In addition,
scientists use fossils
to study the rate at
which evolution has
occurred.
• Paleontologists are
scientists who study
fossils
Ages of Rocks
• Relative age- determine age of rock by
comparing it to other rocks, does not provide
a number
• Example: This rock is older than that rock
• Absolute age- determine actual age of rock in
years
• Example: This rock is 10 million years old
The Position of Rock Layers
• According to the law of superposition, in
horizontal sedimentary rock layers, the oldest
layer is at the bottom. Each higher layer is
younger than the layers below it.
Determining Relative Age
• To determine relative age, geologists also
study extrusions and intrusions of igneous
rock, faults, and gaps in the geologic record.
Determining Relative Age
• An unconformity occurs where erosion wears
away layers of sedimentary rock. Other rock
layers then form on top.
Using Fossils to Date Rocks
• Index fossils must be widely distributed and
represent an organism who existed briefly
• Index fossils are useful because they tell the
relative ages of the rock layers in which they
occur.
The Geologic Time Scale
• Because the time
span of Earth’s past
is so great,
geologists use the
geologic time scale
to show Earth’s
history.
• A mass extinction
known as the
Cretaceous-Tertiary
(K-T) extinction,
ended the Mesozoic
Era.
• It was possibly
caused by a change
in atmosphere due
to an asteroid
striking the earth
The Geologic Time Scale
• Because the time
span of Earth’s past
is so great,
geologists use the
geologic time scale
to show Earth’s
history.
• A Mass Extinction,
known as the
Permian extinction,
ended the Paleozoic
era.
• It was possibly
caused by climate
change due to the
shifting of the
continents