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Evolution and Change
Chapter Fourteen: Earth and Life
History
• 14.1 Evidence from Rocks
• 14.2 How Earth Changes
• 14.3 Natural Selection
Investigation 14A
Relative Dating
• How can you determine the sequence of
past events?
14.1 Evidence from Rock
• Geology is the study of Earth’s formation
and structure.
• Geologists study rocks to find clues to
Earth’s formation.
• Evidence from rocks and fossils allows us to
understand the evolution of life on Earth.
14.1 Evidence from Rock
• In 1666, Nicholas
Steno, a Danish
anatomist, studied a
shark’s head and
noticed that the shark’s
teeth resembled
mysterious stones
called “tonguestones”.
14.1 Evidence from Rock
• Steno theorized that
tonguestones looked
like shark’s teeth
because they actually
were shark’s teeth that
had been buried and
became fossils.
14.1 The formation of
sedimentary rock
• The rock cycle is the
process of rock
formation and
recycling.
• Sedimentary rock
formation is part of
the rock cycle.
14.1 The formation of
sedimentary rock
• Any change in the
composition of material
being deposited shows up
as a distinct horizontal
layer.
• Superposition states that
the bottom layer of
sedimentary rock is older
than the layer on top
because the bottom layer
formed first.
14.1 The formation of
sedimentary rock
• Rock layers may bend or shift and are found
standing vertically, or tilted, or rolled into
curves.
14.1 The formation of
sedimentary rock
• Horizontal layers of rock are continuous.
• By comparing rock layers in the Grand Canyon,
geologists have found that the layers on one side of
the canyon match up with the layers on the other
side.
14.1 Relative dating
• Steno’s principles are
used by geologists to
determine the age of
fossils and rocks in a
process called relative
dating.
• Relative dating is a
method of sequencing
events in the order they
happened.
14.1 Relative dating
• A paleontologist can sequence the organisms
found according to their location in the layers.
• The organisms found in the top layers appeared
after the organisms found in the layers below
them.
14.1 More relative dating
• The idea of cross-cutting
relationships states that a
vein of rock that cuts
across a rock’s layers is
younger than the layers.
• The middle and top layers
formed after the bottom
layer but before the vein.
14.1 More relative dating
• Sometimes rock pieces
called inclusions are
found inside another
rock.
• During the formation of
this rock, sediments or
melted rock surrounded
the inclusion and then
solidified.
• Therefore, the inclusions
are older than the
surrounding rock.
14.1 More relative dating
• Faunal succession
means that fossils can be
used to identify the
relative age of the layers
of sedimentary rock.
• For example, dinosaur
fossils are found in rock
that is about 65 to 200
million years old because
these animals lived that
long ago.