Fossils & The Geologic
Time Scale
Anticipation Guide
• If you agree with the statement, put an √
beside it. If you disagree with the statement,
put an X beside it.
• ____ 1. Fossils show how plants and animals
have changed over time.
• _____2. It is rare for the soft parts of an
organism to become a fossil.
____ 3. A footprint is an example of a trace
fossil.
• ____ 4. A petrified fossil is an animal that
was scared just before it died.
Fossils
• Preserved remains or traces of an organism
that lived in the past.
•Fossils are formed when organisms die and are
buried in sediment. Eventually the sediment
builds up and hardens to become sedimentary
rock.
•Sediments are pieces of solid material that have
been deposited on Earth’s surface by wind, ice,
gravity, or chemical precipitation.
•Paleontologist-scientist who study the remains
of organisms in the rock record.
Kinds of fossils
• Petrified - when minerals replace the remains and
they become rock things like wood.
• Mold - when the shell remains and the contents
dissolve (hollow) like in art class you use a mold
to get the correct shape of a bowl.
• Cast - when the mold becomes filled with minerals
that are not a part of the original organism.
• Index- a fossil found in a narrow time range but
widely distributed around the earth;used to date
rock layers.
• Trace fossil-a fossilized mark that is formed in soft
sediment by the movement or actions of an animal.
PETRIFIED
CAST
MOLD
• Sometimes whole animals become
preserved intact, but this is very rare.
If an organism is surrounded by ice
or tar they might be discovered
looking much the same as they did
when they died.
AETOSAUR
FOUND IN
THE
NATIONAL
PETRIFIED
FOREST
Relative Dating
Relative dating: looks at where the fossil is
located to determine its age relative to other
fossils. This only works if the area has been
undisturbed.
Absolute Dating
• Uses radioactive elements near the fossils
to determine the actual age of the fossils.
•By determining the age of the radioactive
element, scientists can calculate the age of the
fossil buried nearby.
The absolute age
of fossils is
estimated by
dating associated
igneous rock and
lava flows.
Fossil Record
• The dating of all
fossils is included in
the Geological Time
Scale. This scale
divides the time that
the earth has existed
into 4 eras.
• Eras are then divided
into periods based on
common events in
that time period.
Anticipation Guide
If you agree with the statement,
put an √ beside it. If you
Anticipation Guide
disagree with the statement, put an X beside it.
____ 1. An epoch is larger than a period.
____ 2. Periods are the largest division of geologic
time.
____ 3. The smallest period of geologic time is the era.
____ 4. Fossils and rock layers on different continents
are similar.
Vocabulary
• Copy the definitions below in your notebook on
your definitions page.
1. geologic time scale – a model scientists use to
describe the timing of events and the relationships
between those events in earth’s history.
2. era – one of three long periods of geologic time
from Precambrian to the present.
3. period – geologic time periods that eras are divided
into.
4. epoch – a division of geologic time; a subdivision
of a period.
PreCambrian
• Began with
the formation
of the Earth
4.6 billion
years ago.
• Bacteria
appeared 3.5
billion years
ago, followed
by algae and
fungi.
Paleozoic Era
• Divided into 5 periods:
• Cambrian period Sponges, snails, clams
and worms evolve
• Ordovician period First fishes evolved and
other species become
extinct
• Silurian period - Land
plants, insects and
spiders appear
• Devonian period Amphibians evolve and
cone-bearing plants start to
appear.
• Carboniferous period Tropical forests appear and
reptiles evolve.
• Permian period - Seed
plants become common
and insects and reptiles
become widespread. Sea
animals and some
amphibians begin to
disappear.
Mesozoic Era
• Divided into 3 periods:
• Triassic period - Turtles
and crocodiles evolve and
dinosaurs appear.
• Jurassic period - Large
dinosaurs roam the world.
First mammals and birds
appear.
• Cretaceous period Flowering plants appear,
mammals become more
common, dinosaurs
• become extinct.
Cenozoic Era
• Divided into 2 periods:
• Tertiary period - First
primates appear and
flowering plants
become the most
common.
• Quaternary period Humans evolve and
large mammals like
woolly mammoths
become extinct.
ASSIGNMENT
•Read back through the notes you
have just taken. Design 4 multiple
choice questions about the content.
•
•Design one question which asks
for a description or explanation
with details.