Transcript Chapter 5 Section 1 Geologic History

Chapter 5
Section 1
Geologic History
• Objective
• Contrast relative dating
with absolute dating.
• Relative Dating
• Scientists use different
methods to determine the age
of objects in sedimentary
rocks.
• One method, Relative dating,
examines a fossil’s position
within rock layers to estimate
its age.
• The bottom layers of rock
are usually the oldest, and
the top layers are usually
the youngest.
• Scientists can use the order
of rock layers to determine
the relative age of objects
within the layers.
• For example, fossils in
the bottom layers are
usually older than fossils
in the top layers.
• The Geologic Column
• To make relative dating
easier, geologists
combine data from all of
the known rock
sequences around the
world.
• From this information,
geologists created the
geologic column — an ideal
sequence of rock layers that
contains all of the known
fossils and rock formations
on Earth, arranging layers
from oldest to youngest.
• Paleontology
• Paleontology is the science
involved with the study of
past life. Scientists who study
past life are called
paleontologists.
• Paleontologists collect data
by studying fossils.
• Section 2
Looking at Fossils
• Objective
• Explain how fossils can be
used to determine the
history of changes in
environments and
organisms.
• The remains or physical
evidence of an organism
preserved by geologic
processes is called a fossil.
• Trace fossils are any
naturally preserved
evidence of animal activity.
• A cavity in rock where a
plant or animal was buried
is called a mold.
• A cast is an object that is
created when sediment fills
a mold and becomes rock.
• History of Changing Organisms
• Scientists study the relationships
between fossils to interpret how
life has changed over time.
• Since the fossil record is
incomplete, paleontologists look
for similarities between fossils
over time to try to track change.
• Using Fossils to Date Rocks
• Scientists have found that
particular types of fossils
appear only in certain
layers of rock.
• By dating rock layers above
and below these fossils,
scientists can determine the
time span in which the
organism lived.
• If the organism lived for a
relatively short period of time,
its fossils would show up in
limited layers.