Transcript Fossil

Chapter 19, Clues to Earth’s History
• Before we can discuss time
periods of Earth, we must
discuss how we know there are
different time periods….distinct
times where the Earth had
different climates, different land
masses, different plants and
different animals.
What types of things do we study
to make discoveries about the
Earth’s past?
Colonial Coral
Knightia
Pictures from: http://www.mt-vernon.k12.oh.us/High_School/
Depts/Science/frye/fossils/fossil_pictures.htm
Fossils
• Fossil: A fossil
is the remains
or evidence of
a living thing.
• A fossil can be
the bone of an
organism or the
print of a shell.
A fossil might
be a tunnel left
by a worm.
• The most
common fossils
are bones,
shells, pollen
grains and
seeds.
Trilobite
Pictures from:
http://www.mtvernon.k12.oh.us/High_Sch
ool/Depts/
Science/frye/fossils/fossil_pictures.htm
Crinoid
Are fossils found
completely intact?
• Most fossils are not complete.
Why?
• Only the hard parts of dead
plants or animals become
fossils. The soft tissue will
decay or will be eaten before it
can fossilize.
• For most fossils to form, they
must be buried in sediment
soon after the organism dies.
Sediment—What is it?
• Sediment: Particles of rock, shell,
and other materials that are broken
down over time.
• Things that are buried quickly by
sediment are best preserved
because they do not decay.
• Plants and animals that live near
water were preserved more easily
than organisms that are in other
places since they are more easily
covered by sediment.
• Most fossils are found in
sedimentary rock.
Types of Rock
• Sedimentary
Rock: rock
formed by the
compacting or
cementing of
sediments or
other non-igneous
processes at the
Earth surface.
• Igneous rock:
Rock formed by
cooled molten
lava or magma.
• Metamorphic
Rock: Rock that
is changed from
igneous or
sedimentary rock
by heat, pressure
and/or chemical
reactions.
Obsidian—a type of igneous rock
http://www.gpc.edu/~pgore/geol
ogy/geo101/igneous.htm
What type of rock is most
likely to have fossils in it?
• Sedimentary rock is the main
type of rock to have fossils.
• The high temperatures in
igneous rock would tend to
burn up the remains of living
things.
• Likewise, the high
temperatures, pressure and
chemical in metamorphic rock
would eat away at the remains,
leaving nothing to fossilize.
Types of fossils
• Petrification:
The process by
which onceliving material
is replaced by
minerals,
turning it to
stone. (see
page 590)
• Imprints: A
fossil formed
when a thin
object leaves
an impression
in soft mud that
hardens.
Types of fossils continued…
• Mold: What forms
when the soft
parts of an
organism decay
and the hard parts
are dissolved by
chemicals. This
fossil shows only
the shape of the
organism.
• Cast: A fossil that
occurs when a
mold is filled in
with minerals in
the sediment.
This fossil will
have the same
shape as the
organism.
Under what circumstances
can a whole organism be
preserved?
• Freezing
• When
encased in
amber
• When
trapped in
tar pits.
This is a 95 million year old fossil
insect in amber from the Raritan
formation of New Jersey (This
very bug may have bitten a
dinosaur). This is an example of
an organism preserved as
UNALTERED
ORIGINAL MATERIAL
http://www.clas.ufl.edu/users/
pciesiel/gly3603c/fossils.html
• Trace Fossils
A fossil that tells
much about an
animal without
showing any
part of the
animal.
This image shows a
cast of a Dinosaur
footprint from Dinosaur
State Park, in
Connecticut. This kind
of fossil, evidence of
the activity or behavior
rather than the actual
body, is known as a
TRACE FOSSIL (G.
Mead).
http://www.clas.ufl.edu/users/pciesiel/
gly3603c/fossils.html
19.2 History of Fossils
• Law of
superposition:
Law that states
that in
undisturbed
sedimentary rocks
each layer is older
than the one
above it and
younger than the
one below it.
• (see p. 595)
• This law was first
proposed in 1700
by James Hutton
How do we use the Law of
Superposition to study the
Earth’s past?
Is the spiral
shell fossil
older or
younger
than the
cone-shaped
shell fossil?
How do you
know?
Index Fossil:
Fossil of an organism that existed on Earth
for only a short period of time and thus can
be used for scientists to determine the
relative age of a rock.
England
*When the English
Channel was dug,
various fossils were
found on both sides.
Based on these
fossils,
scientists determined
that the English rock
layers were the same
age as the French
layers.
France
1
2
3
4
2
Which 3 fossils helped
them reach this
conclusion?
Which one could not be
used?
See picture on page 597
Can the layers of rock
get out of order?
• Certainly. See page 598.
• Unconformity: eroded rock
surface that is much older than
the younger rock layers above
it. This occurs when the
original layers are bent,
twisted, or folded.
• Fault: A break or crack along
which rocks move. Because
faults occur after rock has
formed, the rock layers are
always older than the faults
they contain.
Other Rock disturbances
• Intrusion: Igneous rock formed by
magna that cools beneath the
Earth’s crust.
Intrusions are younger than the
rock it passes through.
• Extrusions: Igneous rocks formed
from lava that cools at the Earth’s
surface.
Extrusions are younger than the
rock layers beneath them.
• Both intrusions and extrusions
disturb the natural order
“superposition” theory.
Dating of materials
• Originally, scientists tried to
date the layers by saying that a
steady amount of sedimentary
rock was deposited each year.
• If a scientist knew the depth of
sedimentary rock, they could
simply divide the depth by the
total deposited each year to
find the age of the rock.
• What is wrong with this theory?
Radioactive Dating
• Any type of radioactive
element has a nucleus that will
break down, or decay, over
time.
• The amount of decay is a
constant that depends on the
type of element.
• While the amount of sediment
deposited each year is not a
constant, radioactive decay is
a constant.
What is a half-life?
• All radioactive elements have a
thing known as a half-life.
• The half-life of element is: The
amount of time needed for ½ of
the radioactive element to
decay into another element.
• Carbon-14 decays into
Nitrogen.
• If certain radioactive elements
are present in a fossil,
radioactive dating can be used
to judge the age of the fossil.
• All living things have Carbon in
them.
Half-Life Examples:
• Example 1: A fossil is found. If the
radioactive element in it has gone
through 3 half-lifes, how much of
the original substance is left?
First ½ life:
Second ½ life:
Third ½ life:
•Example 2: A 10 gram fossil is found to
have 5 grams of Carbon and 5 grams of
Nitrogen in it. (So the amount of the original
element = the amount of the decay
element). How much of the fossil has
decayed?
•Based on the chart below, how old is the
fossil?
• Example 3: A 20-gram fossil is
found to have 5 grams of Carbon-14
and 15 grams of Nitrogen.
A). What is the ratio of the Nitrogen to
the Carbon?
B). How much (fraction) of the original
material is there?
C). How many ½ lives have occurred?
D). What is the age of the fossil?
• Radioactive elements do not all
have the same ½ lives. (See
page 603).
• Carbon-14 is a radioactive
element that is in all living
things, but it cannot be used to
date all fossils. Why?
• Dinosaurs lived about 200
million years ago. If a dinosaur
skeleton is found, why could
carbon dating not be used to
determine how old the skeleton
is?
• The element used to date the
oldest things will be the one
with the longest ½ life. What is
that?
• Radioactive dating of some
Earth rocks from South Africa
have shown the rocks to be
about 4 billion years old. Moon
rocks have been found to be
between 4 and 4.6 billion years
old. However, it is believed
that the Earth and moon
formed at the same time.
• Thinker: At a dig by a river, the
remains of both a dinosaur and
a human are found. Some
people claim that this is proof
the man and dinosaurs lived
together. How could you prove
or disprove this?
Chapter 19, Clues to Earth’s History
• Before we can discuss time
periods of Earth, we must
discuss how we know there are
different time periods….distinct
times where the Earth had
different climates, different land
masses, different plants and
different animals.
What types of things do we study
to make discoveries about the
Earth’s past?
Colonial Coral
Knightia
Pictures from: http://www.mt-vernon.k12.oh.us/
High_School/Depts/Science/frye/fossils/fossil_pictures.htm
Fossils
• Fossil: A fossil
is the
______________
_____
of a living thing.
• A fossil can be
the _____ of an
organism or the
_____ of a
shell. A fossil
might be a
tunnel left by a
worm.
• The most
common fossils
are bones,
shells, pollen
grains and
seeds.
Trilobite
Pictures from:
http://www.mtvernon.k12.oh.us/High_Sch
ool/Depts/
Science/frye/fossils/fossil_pictures.htm
Crinoid
Are fossils found
completely intact?
• Most fossils are not complete.
Why?
• Only the _____________ of
dead plants or animals become
fossils. The soft tissue will
___________ or will be
_________ before it can
fossilize.
• For most fossils to form, they
must be
_____________________
soon after the organism dies.
Sediment—What is it?
• Sediment: Particles of__________
______________________________
materials that are broken down over
time.
• Things that are buried quickly by
sediment are best preserved
because they do____________.
• Plants and animals that live near
water were preserved more easily
than organisms that are in other
places since they are more easily
covered by sediment.
• Most fossils are found in
______________ rock.
Types of Rock
• Sedimentary
Rock: rock
formed by the
________ or
______________
sediments or
other non-igneous
processes at the
Earth’s surface.
• Igneous rock:
Rock formed by
_________ _____
or ___________.
• Metamorphic
Rock: Rock that
is changed from
igneous or
sedimentary rock
by____________
______________
______________
_____________
Obsidian—a type of igneous rock
http://www.gpc.edu/~pgore/geol
ogy/geo101/igneous.htm
What type of rock is most
likely to have fossils in it?
• _________________ rock is
the main type of rock to have
fossils.
• The high temperatures in
igneous rock would tend to
_______________ the remains
of living things.
• Likewise, the high
temperatures, pressure and
chemical in metamorphic rock
would____________________
_______, leaving nothing to
fossilize.
Types of fossils
• Petrification: The
process by which
once-living
material is
replaced by
___________,
turning it to
_______. (see
page 590)
• Imprints: A fossil
formed when a
_____
___________ leaves
an impression in
soft ______ that
hardens.
Types of fossils continued…
• Mold: What forms
when the soft parts of
an organism
_________ and the
hard parts are
_________ by
chemicals. This fossil
shows only the
_______ of the
organism.
• Cast: A fossil that
occurs when a mold
is filled in with
____________ in the
sediment. This fossil
will have the same
_______ as the
organism.
Under what circumstances
can a whole organism be
preserved?
• ________
• When
encased in
________
• When
trapped in
________
This is a 95 million year old fossil
insect in amber from the Raritan
formation of New Jersey (This
very bug may have bitten a
dinosaur). This is an example of
an organism preserved as
UNALTERED
ORIGINAL MATERIAL
http://www.clas.ufl.edu/users/
pciesiel/gly3603c/fossils.html
• Trace Fossils
A fossil that tells
much about an
animal
____________
____________
___________
This image shows a cast
of a Dinosaur footprint
from Dinosaur State Park,
in Connecticut. This kind
of fossil, evidence of the
activity or behavior rather
than the actual body, is
known as a TRACE
FOSSIL (G. Mead).
http://www.clas.ufl.edu/users/pciesiel/gly3603c/fossils.
19.2 History of Fossils
• Law of
superposition:
Law that states
that in
undisturbed
sedimentary rocks
each layer is
______ than the
one above it and
_______ than the
one below it.
• (see p. 595)
• This law was first
proposed in 1700
by James Hutton
How do we use the Law of
Superposition to study the
Earth’s past?
Is the spiral
shell fossil
older or
younger
than the
cone-shaped
shell fossil?
How do you
know?
Index Fossil:
Fossil of an organism that existed on
Earth for only a ____________________
and thus can be used for scientists to
determine the relative age of a rock
.
*When the English
Channel was dug,
various fossils were
found on both
sides. Based on
these fossils,
scientists
1
determined that the
English rock layers
2
1
were the same age
as the French
3
2
layers.
4
3
Which 3 fossils helped
them reach this
conclusion?
Which one could not
be used?
2
4,
See picture on page 597
2
Can the layers of rock
get out of order?
• Certainly. See page 598.
• Unconformity: __________ rock
surface that is much____________
than the younger rock layers above
it. This occurs when the original
layers are___________________
• Fault: A ____________________
along which rocks move. Because
faults occur after rock has formed,
the rock layers are always
__________ than the faults they
contain.
Other Rock disturbances
• Intrusion: Igneous rock formed by
magna that cools ______________
the Earth’s crust.
Intrusions are _____________
than the rock it passes through.
• Extrusions: Igneous rocks formed
from lava that cools at the Earth’s
___________________.
Extrusions are _____________
than the rock layers beneath them.
• Both intrusions and extrusions
disturb the natural order
“superposition” theory.
Dating of materials
• Originally, scientists tried to
date the layers by saying that a
steady amount of sedimentary
rock was deposited each year.
• If a scientist knew the depth of
sedimentary rock, they could
simply divide the depth by the
total deposited each year to
find the age of the rock.
• What is wrong with this theory?
Radioactive Dating
• Any type of radioactive
element has a nucleus that will
break down, or decay, over
time.
• The amount of decay is a
constant that depends on the
type of element.
• While the amount of sediment
deposited each year is not a
constant, radioactive decay is
a constant.
What is a half-life?
• All radioactive elements have a thing
known as a half-life.
• The half-life of element is: The
amount of time needed for
____________________________
to ___________ into another element.
• Carbon-14 decays into
________________.
• If certain radioactive elements are
present in a fossil, radioactive dating
can be used to judge the age of the
fossil.
• All living things have
_______________ in them.
Half-Life Examples:
• Example 1: A fossil is found. If the
radioactive element in it has gone
through 3 half-lifes, how much of
the original substance is left?
First ½ life:
Second ½ life:
Third ½ life:
•Example 2: A 10 gram fossil is found to
have 5 grams of Carbon and 5 grams of
Nitrogen in it. (So the amount of the original
element = the amount of the decay
element). How much of the fossil has
decayed?
•Based on the chart below, how old is the
fossil?
• Example 3: A 20-gram fossil is
found to have 5 grams of Carbon-14
and 15 grams of Nitrogen.
A). What is the ratio of the Nitrogen to
the Carbon?
B). How much (fraction) of the original
material is there?
C). How many ½ lives have occurred?
D). What is the age of the fossil?
• Radioactive elements do not all
have the same ½ lives. (See
page 603).
• Carbon-14 is a radioactive
element that is in all living
things, but it cannot be used to
date all fossils. Why?
• Dinosaurs lived about 200
million years ago. If a dinosaur
skeleton is found, why could
carbon dating not be used to
determine how old the skeleton
is?
• The element used to date the
oldest things will be the one
with the longest ½ life. What is
that?
• Radioactive dating of some
Earth rocks from South Africa
have shown the rocks to be
about 4 billion years old. Moon
rocks have been found to be
between 4 and 4.6 billion years
old. However, it is believed
that the Earth and moon
formed at the same time.
• Thinker: At a dig by a river, the
remains of both a dinosaur and
a human are found. Some
people claim that this is proof
the man and dinosaurs lived
together. How could you prove
or disprove this?