Name ___________________________
Period _________
Earth’s History
Can we establish a Sequence of Events?
1. Our planet has existed for about _4.5__ billion years. The rocks of
the crust ____preserve clues______ the Earth’s history, its changing
features, and the development of life.
2. By looking at features of rocks, geologists can ___infer___ events of
the past.
3. Uniformitarianism = Forces that acted upon the Earth’s crust in the
___past____ are the ____same_____ as those that are active
today.
“The Present is the Key to the Past”
The Law of Superposition
1. Definition – The rock layers on the bottom are usually
___oldest_____.
a. The relative age of rock strata from bottom to top is usually
____oldest______ to ___youngest____.
2. Rocks are always older than the process that __changed___ them.
3. An extrusion is igneous rock that formed from ____lava_____.
a. An extrusion must be ___younger____ than the strata below
it. This is called the Law of Cross-cutting
4. An intrusion is created when magma is __injected____ into older rock
layers.
a. Intrusions are __younger____ than all of the rock layers in
contact with them.
5. Folds are ___bends____ in the rock strata.
6. Faults are ___cracks_____ in the rock strata.
7. The rock strata MUST be ___older___ than the folds and faults that
have changed them.
8. Fossils are any naturally ____preserve______ remains or impressions
of living things.
a. They are generally found in ___sedimentary_____ rock,
because metamorphic and igneous rocks are formed under
intense pressure and extremely high temps that would
___deform___ or ___destroy____ and fossils.
b. Usually, only the __hard____ parts of an organism get
fossilized, because the soft parts get ___weathered___
before the long process of fossilization takes place.
-Order the geologic events from
oldest to youngest.
1.
2.
3.
4.
5.
__b__
__d__
__c__
__e__
__a__
Geologic Events
a. Deposition and formation of
sedimentary rocks - B
b. Deposition and formation of
sedimentary rocks - A
c. Igneous intrusion of C
d. Tilting of sed. rocks A
e. Contact metamorphism of
sedimentary rocks A
No contact metamorphism
B
A
A
C
Can There Be a Correlation of Rock Strata?
1. Correlation = Matching ___similar______ rock strata in
__different______ locations to see if they formed at the same
___time______ or under similar conditions.
a. “Walking the Outcrop” – Walking from one end of the rock
exposure to the other. Correlation by ___continuity____.
b. Comparing – Comparing the __properties______ of the rock
strata, such as color, texture, or composition.
2. Time Correlation
a. Comparing INDEX FOSSILS contained in the rock strata with
another ___location____. (Note: An index fossil is the remains
of an organism that lived over a wide ___range__ yet lived only
for a brief __time___.)
b. Volcanic ash (bentonite layers) – Volcanic ash falls mark EXACT
___times_________ from one outcrop to another.
Geologic Events of the Past
1. If an area (like Tonawanda) is ___exposed_____ to the surface, then
the rocks begin to be ___destroyed____ by erosion. Erosion causes
____gaps____ in time in the geologic record.
a. When a new layer is deposited, it forms a buried _erosional___
surface called an ____unconformity______.
2. UNCONFORMITY – a buried surface of erosion separating two rock
masses. A.K.A.: A ____gap____ in geologic time.
3. 3 types of unconformities
a. _Angular__ unconformity – Beds are at different angles to the
beds above it.
b. __Disconformity_________ - Missing beds at on site
c. __Nonconformity_________ - When igneous or metamorphic
rocks are in contact with sedimentary rock beds.
The Geologic Time Scale
1. In the 18th and 19th centuries, geologists in Europe noticed that rock
formations could be ____identified_____ by the fossils they
contained.
2. A ___relative______ time scale was established with a sequence of
fossil groups from oldest to ____youngest_______.
3. The geologic time scale is divided into ___eras______,
___periods______, and ___epochs_______.
4. Refer to the Geologic History of New York State at a Glance in the
___ESRTs___. (p.8)
5. An _____orogent_______ is the process of __mountain____
_building________ (p. 9 of your ESRTs)
Evolution of Life
1. Early geologists noticed that the oldest rocks lacked
__fossils________.
2. Fossils of __simple____ _marine____ _organisms__, have been found
in rocks over __3 billion_____ years old.
3. The beginning of the _____Cambrian____ Period marks a production
of complex creatures with __hard___ __parts____.
a. Complex, multi-cellular creatures developed a short time
__before___ this but had not hard parts, so their fossil record
is __incomplete______.
4. As geologist studied the fossil record, they found that more and more
____complex______ organisms developed as time went on.
a. Dinosaurs are never found in the rocks around Buffalo, because
these rocks were deposited _100 million__ years before
dinosaurs even __existed______.
b. The first land animals (other than insects) did not develop until
the ___Devonian___ Period. There are none in older rock
strata.
5. Over __98__% of all fossil types found are of creatures that no
longer exist. These creatures became extinct.
How did modern-day creatures get here?
The most recent fossils look very similar to _modern-day___ plants
and animals, while the ___older_____ fossils become less similar.
This geologic evidence is confirmation that modern-day creatures
have ___descended____ from more primitive creatures.
Taken further, it supports Charles Darwin’s theory that all life
descended from an ancient __common____ ancestor.
6. Human existence has been _very__ _brief__ in comparison with the
expanse of geologic time.
7. The fossil record ___supports____ Darwin’s theory on organic
___evolution_____.
a. Evolution is a hereditary ___change____ in a population
through successive generations.
b. Darwin proposed that guiding the change is a mechanism, called
___natural____ __selection____.
8. Natural Selection
a. All species have _____variations_______ in size, shape, and
other traits.
b. When the environment puts a __stress_____ on a species,
certain variations (__traits___) will be better
___adapted____.
c. Individuals with these desirable variations have a better chance
to ___survive_____ than individuals without the variations.
d. After many generations, this population may _change___ into a
new species, which is called ___speciation____.
9. When stress is put upon the environment, like an asteroid/comet
impact or major volcanic explosion, a species will either adapt to the
new stress and evolve, or go __extinct_________.
What is Radioactive Dating?
1. Fossils could not tell geologists how ___long____ ago, in years,
organisms lived or how long ago rock strata formed.
2. Natural radioactivity in rocks can give an __absolute____ _age_
measured in years.
3. Chemical elements come in several different forms, called
_isotopes__ that differ in the number of neutrons in the nucleus.
a. Carbon 12 atom - _6_ protons and _6__ neutrons in nucleus.
b. Carbon 14 atom - _6_ protons and _8__ neutrons in nucleus.
c. Some isotopes can be __unstable__ and will break apart. The
isotope is considered __radioactive__, and breaks down into a
lighter element called a __decay___ __product____.
d. In the process, it gives off ___radioactivity_____.
4. A radioactive isotope decays at a ___constant_____ rate, and is
measured by its half-life.
5. A half-life is the time required for __half__ of an element’s atoms in
a sample to __change___ to the decay product.
a. As the element decays (blue), __fewer___ radioactive atoms
remain in the sample, and more and more decay product (red)
___accumulates____.
6. The decay-product ratio is the ratio between the ___mass___ of the
radioactive element and its decay product.
a. If a wood sample contains equal amounts of carbon 14 and its
decay product, nitrogen-14, then the wood must have gone
through one ___half-life____.
b. If the wood sample contains one-quarter C-14 and threequarters N-14, then it has undergone ___two___ half-lives.
7. Laboratory studies show that the half-life fro each element is not
affected by __environmental_____ conditions, such as temperature,
pressure, or chemical combinations.
8. Radioactive isotopes with short half-lives are good for dating
relatively __recent_____ materials, whereas those with longer halflives are useful for dating ___older_____ rocks.
9. Radioactive Decay Data is on the front page of your ESRT’s.
Regents Questions:
-A marine fossil was found to contain one-half of its original
quantity of Carbon-14. Approximately how old is this fossil?
5,700 years
-A volcanic ash layer was found to contain one-quarter of its
original quantity of Potassum-40. How many half-lives has the
ash layer undergone?
Two half-lives
-Approximately how long ago did the volcano erupt?
1.3 billion X 2 = 2.6 billion years