Chapter 3
The Rock and Fossil Record
Sections 1-5
Pages 58-89
Principle of Uniformitarianism
• The Principle of
Uniformitarianism – a
principle that states that
geological processes that
occur in the past can be
explained by current
geological processes
• James Hutton wrote Theory
of Earth about the
processes that we observe
(erosion and deposition)
remain uniform (do not
change) over time
Uniformitarianism vs.
Catastrophism
• Uniformitarianism did
not gain acceptance
until Charles Lyell
published Principle of
Geology in 1833 to
prove Hutton correct
with his new evidence
• Catastrophism:
principle that states
geological change
occurs suddenly and or
rapidly
• Remained Geology’s
guided principle until
1830’s
Modern Geology
• Late 20th century:
Stephen Gould indicated
that while most of Earth’s
history is gradual,
sometimes catastrophes
play a part
( asteroid striking Earth,
change global climate or
cause extinction)
• Mixture of both
uniformitarianism and
catastrophism
Paleontology- study of past life
(fossils)
• http://www.youtube.co
m/watch?v=B7zo2zY1Z
qg
Relative Dating
• Determining whether
an object is older or
younger than other
objects or events
• Geologists use rocks
and fossils
Principle of Superposition
• The principle that states
that younger rocks lie
above older rocks in
undisturbed sequences
• However, sometimes
the oldest rocks are not
on the bottom due to
geological forces
(tilting, folding and
breaking)
Geological Column
• Used to help geologists,
they combine data from
all the known
undisturbed rock
sequences around the
world
• Geologists use the
geological column to
interpret rock sequences
and to identify layers in
puzzling rock sequences
Disturbed Rock Layers
• Geologists use the
relationship between rock
layers and the features
that cut across them to
assign relative ages to the
features and the layers
• Faults, intrusions, folding
and tilting are examples
of features that cut
across rock layers
Gaps in the RecordUnconformities
• Missing rock layers create
breaks in rock-layer sequences
called unconformities
• An unconformity is a surface
that represents a missing part
of the geological column
• Unconformities also represent
missing time
• Nondeposition- stoppage of
deposition when a supply of
sediment is cut off
• Erosion- (wind and water)
allow deposition
Types of Unconformities
• Disconformities: part of a
sequence of parallel rock is
missing. (thousand to millions of
years)
• Nonconformities: found where
horizontal sedimentary rock
layers lie on top of eroded surface
of older intrusive ingenious or
metamorphic rock. (millions of
years)
• Angular unconformities: found
between horizontal and
sedimentary rock layers and rock
layers that have been tilted or
folded. (millions of years)
Absolute Dating
• The process of
establishing the age of
an object by
determining the
number of years it has
existed is called
absolute dating.
Radioactive Decay
• Unstable isotopes:
radioactive
• Radioactive isotopes tend to
break down into stable
isotopes of the same or
other elements in a process
called radioactive decay.
• Occurs at a steady rate,
scientists use the relative
amounts of stable and
unstable isotopes present in
an object to determine the
object's age.
Dating Rocks
• After the unstable isotope breaks
down into a stable isotope, the
stable isotope may be of the
same element or more often a
different element.
• The unstable radioactive isotope
is called the parent isotope.
• The stable isotope produced is
called the daughter isotope.
• Rate of decay is constant.
• Scientists compare the amount of
parent isotopes to the daughter
isotopes to determine the age of
rock. The more daughter
material, the older the rock is.
Radioactive Decay
• http://www.furryelephant.com/player.php?su
bject=physics&jumpTo=re/15Ms1
Radiometric Dating
•
•
•
•
If you know the rate of decay for a
radioactive element, you can determine the
absolute age of the rock.
Based on a parent to daughter ratio, you can
determine the absolute age, this process is
called radiometric dating.
A half life is the time that it takes one half of
the radioactive sample to decay.
After every half-life, the amount of parent
material decreases by one-half.
½, ¼, 1/8, 1/16
Try this example: Carbon 14’s half-life is 5, 730
years. How old will the object containing this be
when ¼, 1/8, 1/16, 1/32 of it’s Carbon 14
remains.
Types of Radiometric Dating
• Potassium Argon Method:
used for rocks older than
10,000 years old.
• Uranium Lead Method:
used for rocks more than
10 million years old
• Rubidium Strontium
Method: used for rocks
over 10 million years old
• Carbon 14 Method: used
for dating living things
that lived within the last
50,000 years
Fossilized Organisms
• A fossil is the remains or
physical evidence of an
organism preserved by
geological processes
• Fossils in rock: sometimes
decaying organisms get quickly
buried by sediment (rock),
then the sediment becomes a
rock. The harder parts of the
animal (bones) become well
preserved in this newly
formed rock.
• Fossils in amber: Organisms
(insects) get caught in soft
sticky tree sap which hardens
and preserves them.
Fossilized Organisms
• Petrifaction: process in
which minerals replace an
organism’s tissues.
• Permineralization is when
pore space of an
organism’s hard tissue
bone or wood) is replaced
with minerals.
• Replacement is when the
organism’s tissues are
completely replaced by
minerals. (Petrified wood)
Fossilized Organisms
• Fossils in Asphalt: thick,
sticky pools of asphalt on
Earth’s surface (La Brea in
Los Angeles), trapped and
preserved organisms from
38,000 years ago!
• Frozen Fossils: the last ice
age has preserved many
types of fossils since the
extreme cold drastically
slows down decay
(Wholly Mammoth,
Siberian tundra)
Trace Fossils
• Any naturally preserved
evidence of animal
activity is called a trace
fossil.
• Tracks
• Burrows
• Coprolite (animal dung)
Molds and Casts
• A mold is a cavity in
rock where a plant or
animal was buried.
• A cast is an object when
sediment fills a mold
and becomes rock.
Using Fossils to Interpret the
Past
• The fossil record is incomplete
because most organisms never
became fossils…and some have
not been discovered.
• The fossil record helps reveal a
history of environmental change.
Using the fossils of plants and
land animals, scientists can
reconstruct past climates.
• To fill in the missing information
about changes in organisms in
the fossil record, paleontologists
look for similarities between
fossilized organisms or between
fossilized organisms and their
closest living relative.
Using Fossils to Date Rocks
• Index fossils are fossils
of organisms that lived
during a relatively short,
well-defined geological
time span.
• Ammonites: tropites
(mollusk/squid like),
230-208 mya
• Trilobites: phacops
(horseshoe crab) 400
mya
Geologic Time
• The layers in the Grand
Canyon represent
nearly 2 billion years of
Earth’s history.
• Well preserved plant
and animal fossils are
common in Green River
because of fine-grained
lake-bed sediments.
Geological Time Scale
• The Geological Time
Scale accounts for
Earth’s entire history.
• It is divided into 4 major
parts called eons.
• Dates are estimates.
• Represents about 4.6
billion years of Earth’s
history.
Divisions of Time
in size order (greatest to smallest)
• Eons: largest division of
time, 4 major eonsHadean, Archean,
Proterozoic, and
Phanerozoic.
• Era: there are 3 eras in
the Phanerozoic Eon
• Periods: the 3 eras are
divided into periods
• Epochs: the periods are
divided into epochs
Extinction
• The death of every
member of the species.
• Can be caused by global
change and/or change
in ocean currents
Paleozoic Era
•
•
•
•
•
Marine life flourished
Land plants appeared
Amphibians and reptiles
Insects
Largest mass extinction
in Earth’s
history….cause? Ocean
currents?
Mesozoic Era
•
•
•
•
Age of the Reptiles
Small mammals
Dinosaurs and birds
Extinction….cause?....
Global climate?
Cenozoic Era
• Age of Mammals
• Mammals competed
with dinosaurs
• Due to climate
change…mammals
better suited for
environment