Transcript T5 Fossils & the Rock Records

T5 Fossils & the Rock
Records
...it’s as old as the hills.
PowerPoint Notes created by S. Koziol
Date : 12/1/2013 Revised : ?/?/??
Part 1 Objectives
• Describe the geological time scale
• Distinguish among the following time
scale divisions: eon, era, period & epoch.
The geologic time scale
divides Earth’s
history into units
from its origin to the
present.
Era
Period
Quatern
ary
Cenozoic
Tertiary
Epoch
Holocene
Time Scale – To be Completed
1.8
Pliocene
5.3
Miocene
23.8
Oligocene
33.7
Eocene
54.8
Cretaceous
Mesozoic Jurassic
Triassic
Permian
Carboniferous
Pennsylvanian
Carboniferous
Paleozoic Mississippian
Devonian
Silurian
Ordovician
Cambrian
Precambrian time
Adapted from Modern Earth Science, 2002, Holt, Rinehart and Winston
0.011
Pleistocene
Paleocene
Time Scale
Began (MYA)
65
144
206
248
290
323
354
417
443
490
540
4600
Era
Period Epoch
Began (millions of years)
Characteristics from
geologic and fossil
evidence
Blank Time Scale
0.011
1.8
5.3
23.8
33.7
54.8
65
144
206
248
Connecticut Valley
Geological Events
Era
Period
Began (millions of years)
Characteristics from
geologic and fossil
evidence
Time Scale Continued
290
323
354
417
443
490
540
4600
Adapted from Modern Earth Science, 2002, Holt, Rinehart and Winston
Connecticut Valley
Geological Events
Recent period
The most recent period is the Quaternary
Epoch
On the geologic time scale, the smallest unit of
time is called an epoch - longer than an age
and shorter than a period.
Phanerozoic Eon
The Phanerozoic
Eon includes the
Paleozoic,
Mesozoic, and
Cenozoic Eras
EON
ERA
4 total, half a
billion years or
more
10 total, several
hundred million
years
PERIOD
EPOCH
tens of millions of
years
AGE
millions of years
Eons
The Archean and Proterozoic are examples of
eons
End of the Precambrian
The end of the Precambrian is marked by the
appearance of organisms with hard parts.
Cloudina, the earliest
known calcium carbonate
shell-bearing fossil.
Units of
geologic time
Era
Period
Quaternary
Cenozoic
Units of geologic
time in order
from shortest to
longest
• epoch, period,
era, eon
Tertiary
Epoch
Holocene
Paleozoic
0.011
Pleistocene
1.8
Pliocene
5.3
Miocene
23.8
Oligocene
33.7
Eocene
54.8
Paleocene
Mesozoic
Began (MYA)
65
Cretaceous
144
Jurassic
206
Triassic
248
Permian
290
Carboniferous
Pennsylvanian
323
Carboniferous
Mississippian
354
Devonian
417
Silurian
443
Ordovician
490
Cambrian
540
Precambrian time
Adapted from Modern Earth Science, 2002, Holt, Rinehart and Winston
4600
Periods
Periods are defined
by the abundance
or extinction of lifeforms.
Eras vs. Periods
Both are units of time on the geologic time scale.
Eras
are longer spans of time,
measured in hundreds of
millions to billions of
years. They are defined
by differences in lifeforms found in rocks.
Periods
are usually measured in terms
of tens of millions of years
to hundreds of millions of
years. They are defined by
the life-forms that were
abundant or became extinct
during the time in which
specific rocks were
deposited.
Part 2 Objectives
• Apply the principles for determining
relative age to interpret rock sequences.
• Describe an unconformity and how it
formed within the rock record.
Oldest rock layer
The oldest rock layer in an undisturbed rock
sequence occurs at the bottom of the
sequence
The Principle of Superposition
The principle of superposition states that, in an undisturbed
sequence, the oldest rocks are at the bottom of the sequence
and successive layers are younger than those below them.
Cross-cutting Relationships
You can use the principle of cross-cutting
relationships to infer that a fault or an
intrusion is younger than the rock it cuts
across.
Correlation
The matching of rock layers from one geographic
area with those of another area is known as
correlation.
Inferences and rock layers
Uniformitarianism
The principle of uniformitarianism states that the
processes occurring today have been occurring
on Earth since it formed. However, the rate,
intensity, and scale with which these processes
occur have changed.
Unconformity
When part of the rock record is destroyed, the
erosional gap that forms is an unconformity.
Angular Unconformity
The gap in the rock record that occurs between
folded or uplifted rock layers and a
sedimentary rock layer on top of them is called
an angular unconformity.
Nonconformity
A buried erosional surface between a
nonsedimentary rock and a sedimentary rock
is called a nonconformity.
Part 3 Objectives
• Explain the several different methods
used by scientists to determine absolute
age.
• Describe how objects are dated by the
use of certain radioactive elements.
• Explain how annual tree rings and glacial
varves are used to date geological
events.
Half Lives for Radioactive Elements
½ Life
The amount of time it takes for one-half of the original amount of
an isotope to decay is known as its half-life.
Radioactive Parent
Stable Daughter
Half life
Potassium 40
Argon 40
1.25 billion yrs
Rubidium 87
Strontium 87
48.8 billion yrs
Thorium 232
Lead 208
14 billion years
Uranium 235
Lead 207
704 million years
Uranium 238
Lead 206
4.47 billion years
Carbon 14
Nitrogen 14
5730 years
½ Life Practice Sheet
Absolute dating
Radiometric dating is used to determine the
absolute age of a rock
Key Beds
A key bed contains distinctive material that
geologists can easily recognize in the rock
record and use as a time marker.
Contrast relative-age dating and
absolute-age dating.
Relative-age dating
Relative-age dating places the
ages of rocks and the events
that formed them in order,
without exact dates. This is
done by comparing one
event with another or one
rock with another rock.
Absolute-age dating
In contrast, absolute-age
dating determines the
actual age of a rock, a fossil,
or an object. This is done
through radiometric dating,
a process that determines
the ratio of parent material
to daughter product in a
given sample of rock or
fossil.
Part 4 Objectives
• Define fossil.
• Explain several methods by which fossils
can be preserved.
• Describe the characteristics of an index
fossil.
• Discuss how fossils can be used to
interpret Earth’s past physical and
environmental history.
Fossils
Fossils are the remains or evidence of onceliving plants or animals. They provide clues
about Earth’s past environmental conditions
and evolutionary changes in organisms over
time. They also help to correlate rock layers
from one area to another.
Fossils (continued)
Fossil insects preserved in hardened tree sap are
called amber.
Fossils (continued)
Molds, casts,
coprolites, and
petrified wood are
all example of fossils
Fossils - original preservation
Mummified animals found in dry caves can be
examples of fossils with original preservation.
Fossils - original preservation
Fossil insects can be found imbedded in amber,
the hardened sap of prehistoric trees.
An insect imbedded in amber is an example of a
fossil with original preservation.
Fossils (altered)
An example of a fossil with altered hard parts
includes petrified wood
Trace Fossils
An example of a trace fossil includes worm trails.
Permineralization
In the process of permineralization, pore spaces
within an organism’s shell are filled in with
mineral substances.
Fossils - casts
A cast forms when the hollowed-out impression
of a fossil organism becomes filled with
minerals or sediment.
Fossils - molds
When the original parts of an organism in a
sedimentary rock are weathered and eroded,
a hollowed-out impression called a mold
forms.
Index fossils
Index fossils are useful to geologists if the fossils
have lived over a short period of time
Index vs. Trace Fossils
Both are similar in that they are types of fossils.
Index fossils
are the remains of organisms
that can be used by
geologists to correlate rock
layers over large geographic
areas or to date rock layers.
Trace fossils
are not remains but indirect
evidence of organisms,
such as imprints, trails,
and burrows.
Evolution
The adaptation of life-forms to changes in the environment is
known as evolution.
A process by which (generations of) organisms adapt to changes in
their environments.