 Most commonly found in Sedimentary
Rock.
 As time passes, more layers are dropped on
top of old layers.
 This means newer fossils on top old fossils.
 remnants or traces of organisms that are preserved in
layers of rock.
 If an organism gets buried under sediment, the soft
parts will decay, while the hard parts (bones, teeth,
etc.) undergo a chemical change to become preserved
in the sediment, which later becomes rock.
 provide a variety of information that scientists can use
to learn about the organisms that once lived on Earth.
 the growth stages of an organism throughout
its life cycle
 the microscopic features of an organism, such
as cell structure
 the roles that organisms played within
communities and food chains
 how organisms have changed over time
 the different types of organisms that lived at
different times
 the appearance of the organism and its
structures, including information about bone
structure and organs
 Geologic eons, eras, periods, and epochs are each
associated with changes among the organisms that
lived on Earth.
 The types of organisms that were present in
various periods of Earth's history can provide
information about changes in the Earth's climate.
Many organisms, for example, are known to
survive within certain temperature ranges. If
fossils of those organisms are plentiful, then
scientists gain an important clue about the typical
temperatures during that time period.
 Fossils of plants and animals in Antarctica, for
example, show that a long time ago it had a
warmer climate.
 provide information about how the Earth's
surface has changed over time.
 If fossils of marine organisms are found in
areas that are now dry land, scientists may
assume that the area was once under water.
 This gives scientists important clues about
land elevation, landforms, and sea level at
various times in Earth's history.
 Fossils also show how the continents of the
Earth have moved over time.
 The image above shows the approximate locations of
the Earth's continents as they would have appeared
250 million years ago, prior to the rise of the dinosaurs.
 Age is relative to the age of something around it.
 Principle of Superposition – states the rock layer
above is always younger. Rock layer under is always
older. Does not apply when rocks are turned upside
down or disrupted.
 The principle of original horizontality states that
sediment is deposited in horizontal
layers. Sedimentary rocks form as horizontal rock
layers from this sediment.
 allows geologists to recognize when rock layers have
been moved from their original positions.
 rock layers that slant at an angle, he or she knows that
the layers have been tilted from their original,
horizontal position.
 The principle of cross-cutting relationships states that
a geologic feature is younger than the features it cuts
across. For example, a fault that cuts across rock layers
is younger than the rock layers.
 Absolute dating is a method in which the
age of an object or event is estimated as an
actual number of years. For example, a
geologist might determine that a layer of
volcanic ash is 20 million years old
 Radioactive dating, or radiometric dating,
is a method in which the age of a rock,
mineral, or fossil is calculated based on the
amounts of certain radioactive substances in
the sample compared to other substances in
the sample.
 Radiocarbon dating is a type of radioactive dating that
uses different types of carbon to measure the age of
fossils or other materials. Radiocarbon dating relies on
the fact that carbon-14 is radioactive and decays at a
predictable rate.