Earth Science Earth’s History Notes

I. Introduction a. As we already learned the earth is always changing b. The history of the earth is told by _________________

___________________________________________c. It is up to the scientist to figure out the puzzle of these

geological events. II. Early Earth

a. There is evidence that states that the atmosphere and the oceans of the early earth ___________________________ _______________________ _________________________ _________________________ _________________________

b. There were large amounts of i. ____________________ii. ____________________iii. _____________________iv. _____________________

That came out of the earth from a process called ___________

v. The vapor was ________________________________ ___________________________________________

c. The early earth was also covered by clouds that formed precipitation over millions of years that cooled down the hot surface of the earth and also formed oceans.

d. What is the proof to this?i. _________________________________

__________________________________ __________________________________

e. Today’s atmosphere is made up of 21% oxygen but the gases of eth volcanic eruptions do not contain oxygen

i. SO WHERE DID WE GET THE OXYGEN FROM?1. ________________________________________________

__________________________________________________________________

a. Photosynthesis produces extra oxygen that went into the atmosphere over millions of years.

III. Sequence of Geological eventsi. Knowing the sequence of events that took place

during the formation of the earth’s crust helps us develop a history of the earth to better understand the earth

- 1 -

Earth Science Earth’s History Notes

ii. Relative age is _______________________________ __________________________________________

1. As shown in the appearance of the rock layers2. Relative age is not really concerned with the

age of the rocks ______________________________ ______________________________________

3. This method uses a. sedimentary rock layersb. igneous extrusions and intrusionsc. faults d. folds e. continuity f. similarities of rock g. fossil evidence h. and volcanic time markers

As clues to determine what was the probable sequence of events

iii. The actual age of a rock or a fossil is called __________1. The best way and more precise ____________

___________________________________ ___________________________________

2. EVERY RADIOACTIVE ELEMENT DECAYS 3. How does this work?

a. _______________________________ __________________________________________________________

b. Sometimes this changing process goes through steps

c.d. We also know how _________________

_______________________________e. We use a process of half life. Since we

know how long the half life ( time takes ½ the isotope to decay) is ______________ __________________________________________________________________

b. Chronology of layersi. The law of superposition

1. ________________ ________________ ________________ ________________

a. This is used to determine the sequence _______ _________________________________

- 2 -

Earth Science Earth’s History Notes

b. This works as long as the group was not overturned not had an older rock put over it

c. Igneous Intrusions and Extrusions i. Igneous Intrusions

1. formed when magma is injected into older rock layers in the crust

2. younger than rock they are found in 3. look for contact metamorphic rock in layer

above and below the intrusionii. Igneous Extrusions

1. rocks that ______________ ______________________2. younger than rock layers

below3. ______________________

______________________iii. Why do we look at the

metamorphic rock near these two rock formations?

1. The reason is contact metamorphism – (the rock forming due to the contact of lava) ________________________________

d. Faults Joints & Folds i. Folds

1. bends ______________2. occur ______________

___________________ii. Faults

1. cracks in rock layers where some movement has taken place

2. Faults produce offset layers.

iii. Joints 1._________________________

iv. These three rock layer characteristics occur _________ ______________________________________________________________________________________

v. These three rock characteristics are also ___________ ___________________________________________

1. Since the rocks that fold, faults or joints are there before ________________

e. Internal Characteristics

- 3 -

Earth Science Earth’s History Notes

i. Fragments that occur in a rock as we can understand are older than __________________________________ ________________________________

ii. Cracks and veins in a _________________ _________________________________

iii. Veins – are mineral ____________________________ _________________________________________

iv. Sedimentary rocks are ________________________ __________________________________________.

v. Unconformity 1. Is the ________________________________ 2. They are found between two ages of rock

levels3. Usually these ______________________

___________________________________4. It looks like a buried Erosional

surface5. ________________________

________________________

______________________________________ -______________________________________

IV. Relative Agea. We use different correlating techniques to find out how old

a rock really is b. You have to be careful though to use facts and not

inferences when figuring out this information i. Correlation is the act of matching rocks of similar age

in different places 1. This is best done when rocks are not covered in

dirt and plants 2. This can be so easy by identifying a certain

mineral type, color and then searching for it in different places

ii. one technique is called INDEX FOSSILS a. this is using

the remains of animals that are known to have lived and died in a certain time period

- 4 -

Earth Science Earth’s History Notes

b. If we find one ____________ ____________ ____________ ____________ ____________

c. We also use Index fossils to decipher rock records

i. Organism ___________________________ ________________________________________________________

d. How does a fossil fit the index profile i. Easily recognizableii. _______________ iii. ________________ ________________ iv. _______________

___________________________iii. Volcanic Time Marker

1. When a volcano ________________________ ____________________________________ ____________________________________

2. This may be a time marker if we find a layer of ash in the layers ___________ ______________________________ ______________________________

3. This time marker will be very helpful determined the ages of rocks below and above it

iv. Problems with Correlation 1. It _________________________________

___________________________________________________________________________

2. However, it can lead to misinformation a. With very careful study of 2 like rock

formation they might still be different ages.

b. ________________________________ ________________________________

V. Geological Times a. Rock Record

i. As we just learned that scientist use index fossils (guide fossils ) to tell how old a rock is.

ii. Scale of geological time 1. scientists have organized the geological time

scalea. ________________ b. ________________ c. ________________

- 5 -

Earth Science Earth’s History Notes

d. ________________2. each is a more specific amount of time then

the other ones

a. epochs are more based on fossil evidence

i. However, most of the geological time is void of fossil records

iii. Scientists suggest the following is the geological time scale

1. Precambrian (prepaleozoic) era a. Makes up 85% of the earth’s history b. ______________________________

______________________________i. This is because the organisms

______ ________________________________________________________

2. Paleozoic eraa. Much shorter time period b. Has an abundant of fossils

c. The first vertebrates, land plants and

animals developed in this era 3. The Mesozoic Era

a. Was even shorter

- 6 -

Units of geological time periods

Phanerozoic eon Proterozoic eon

Cenozoic

Archean eon

Mesozoic Paleozoic

cretaceous

Jurassic

Triassic

Earth Science Earth’s History Notes

b. Fossils of dinosaurs and the earliest birds and mammals formed

c. Included three periodsi. Triassicii. Jurassic iii. Cretaceous

4. The Cenozoic Era a. Most recent era b. Includes the fossils of many modern

plants and mammals, even the appearance of humans

i. Plate motions and mountain buildings may also be identified in this time sequence by using the reference table

b. The Erosional Record i. Buried erosional surfaces show gaps in the time

records of the rocksii. It has been suggested that the fossil record would

show a complete timescale and history of earth IF………………….

1. the superposition and held absolutely true2. no forces of destruction occurred after the the

beginning of life forms iii. but it is clear that destructional forces have occurred

and continue to occur iv. One of the key principles that geologists use to

interpret the Earth’s geological history is the principle of uniformitarianism

1. This principle states that the geological processes that change the earth today also changed the earth in the past

2. There are many different rates and various times but patterns and agents of change stay the same

c. The geological history of an area i. Using the information used in the rock record,

scientist can guess the history of an area ii. To see the various rock portions if NEW YORK check

out your reference guide

- 7 -