Download Happy Tuesday! Pull out a ½ sheet of paper or share a whole with

Happy Tuesday! Pull out a ½ sheet of paper
or share a whole with your neighbor.
Weekly Schedule
Today
Quiz # 2
Relative Dating
Age of the Earth
Geotimeline Act
Thursday
Radiometric
Dating
Geologic dating
methods lab
WORK WITH A CLASSMATE TO PUT THIS LIST OF
EVENTS IN CHRONOLOGICAL ORDER:
• MOTHER’S BIRTH
• GRANDFATHER MEETS GRANDMOTHER
• MOTHER MEETS FATHER
• MY HIGH SCHOOL GRADUATION
• MY GRANDFATHER’S BIRTH
(THERE ARE CERTAIN CONDITIONS THAT MUST BE TRUE
FOR A SEQUENTIAL EVENT TO OCCUR)
LIKEWISE THERE ARE A SET OF PRINCIPLES THAT
GOVERN THE DEPOSITION OF ROCK ON EARTH
Geologic Time
Relative ages—based
upon order of formation
Qualitative method
developed hundreds of years
ago.
Permit determination of older
vs. younger relationships.
Numerical ages—actual
number of years since an
event
Quantitative method
developed recently.
PRINCIPLE OF UNIFORMITARIANISM:
“The present is key to the past.”
-James Hutton
• Processes seen today are the same as those of the
past.
PRINCIPLE OF SUPERPOSITION:
• Younger sedimentary rocks overlie older rocks
Examine the image of rock layers below. Which
letter represents the layer that was formed
earliest?
1. A
2. B
3. C
4. D
Image courtesy of USGS
PRINCIPLE OF ORIGINAL HORIZONTALITY:
Sedimentary rocks are deposited relatively horizontal
Folds and tilting must
postdate deposition
Examine the image of rock layers below.
Tilting must have occurred
1. After A was
deposited
2. Between the
deposition of E
and A
3. before B was
deposited.
4. between
deposition of
layers C and E.
PRINCIPLE OF LATERAL CONTINUITY
• Sedimentary rocks accumulate in continuous sheets
These layers once spanned the canyon at
one time
Examine the image of rock layers below.
Which statement is most accurate in
regard to rocks located at A and B?
1. A is older than B
2. B is older than A
3. A and B are the same age
PRINCIPLE OF CROSS-CUTTING
RELATIONSHIPS:
•
A feature that cuts across another is younger
than that it cuts
Dike = an igneous
intrusion that cuts
across preexisting rock
Is the dike older or
younger than the
surrounding rock?
Examine the image of rock layers below.
Which letter represents the rock unit that
was formed most recently?
1. A
2. B
3. C
PRINCIPLE OF INCLUSIONS:
Igneous and sedimentary rocks that contain inclusions of
other rocks must be younger than the rocks they include
The embedded rocks (inclusions) in the
sedimentary layers are:
A. metamorphic.
B. older than the sedimentary
layers.
C. younger than the sedimentary
layers.
D. the same age as the layers.
The Principle of Fossil Succession
Fossils are often preserved in sedimentary rocks.
Fossils are time markers useful for relative age-dating.
Fossils speak of past depositional environments.
Specific fossils are only found within a limited time
range.
Unconformities
• Gaps in the rock record
are called
unconformities.
• EROSION OR NONDEPOSITION
• An angular unconformity
happens when tilted or
folded rock is covered by
younger, horizontal rock.
Examine the image of rock layers below. An
angular unconformity is present between layers
___ and ___.
1. A and E
2. B and D
3. C and F
4. F and D
Correlating Formations
Earth history is recorded in sedimentary strata.
The Grand Canyon has thick layers of strata and numerous gaps.
Formations can be correlated over long distances.
Fig. 10.6a
Geologic Time
The geologic time scale—a
“calendar” of Earth history.
• Originally created using
relative dates
• Specific dates using
radiometric dating
• Subdivides geologic history
into units:
Eons, eras, periods, and
epochs based on changes
in life forms
Precambrian Time
The Precambrian ranges from 4.5
billion years ago to ~543 million years
ago.
• ~90% of Earth’s history
• Considerable volcanic
activity
• Meteorite bombardment
• Cyanobacteria
• Soft-bodied organisms
• Primitive atmosphere and
ocean
• Beginnings of lithospheric
plate formation and
movement
The Paleozoic Era
Spans ~300 million years. Six periods:
Periods are marked by changes in:
• In life forms, tectonics, and changes in sea level—rise and fall of
sea level.
The Mesozoic Era
Mesozoic era spans ~180 million years from 248 Ma to
65 Ma
Often called the “age of reptiles” -first true terrestrial
animals
•
•
•
•
Dinosaurs dominated.
One group of reptiles led to the birds.
Many reptile groups, along with many other animal
groups, become extinct at the close of the Mesozoic.
Possible Hypotheses for Extinction:
— Impact from large asteroid or comet.
— Extensive volcanism.
The Cenozoic Era
Cenozoic—a smaller fraction of geologic time than the
Paleozoic or Mesozoic
• 65 million years ago to the present
• Often called the “age of mammals”
• Pangaea’s breakup complete
•
•
•
One-third of the land covered by ice
Marine mammals and large land animals evolved
Humans evolved