Earth Science Regents ReviewUnit 5

Sequence of Events

• Principle of Superposition: older layers are on the bottom

• Law of Original Horizontality: sedimentary layers are all horizontal before crustal movement

• Law of Cross Cutting Relationships: whatever cuts across a layer is younger than the layer

• Principle of Uniformitarianism: the way geologic events happened in the past happen in the same way today.

An unconformity is a buried erosional surface. It is usually represented by a squiggly line in between layers. The steps are as follows: • uplift and emergence •weathering and erosion•subsidence and submergence•deposition of _______________

How did this form?

6) Subsidence and submergence5) Deposition of shale4) Deposition of sandstone3) Intrusion and contact metamorphism2) Uplift and emergence1) Weathering and erosion

6) Subsidence and submergence5) Formation of limestone4) Deposition of shale3) Deposition of sandstone2) Intrusion and contact metamorphism1) Faulting of layers

1) _________________is the matching of strata through fossils or characteristics of the layers to prove that they were once part of the same outcrop.

What are index fossils?

These are fossils found in many locations but only existed for one geologic time period. They are excellent time

markers.

Volcanic AshUseful because volcanic ash could cover large areas in a very small period of time (days to weeks) and each volcano has a mineral “fingerprint” it is very useful in correlation

12 2

33

3

44

55 6

7788

8

99

1010

The diagram below shows a fossil found in the surface bedrock of New York State.

Which other fossil is most likely to be found in the same age bedrock?1.Phacops2.condor3.Coelophysis4.Tetragraptus

1. 2. 3. 4.

Which fossil may be found in the surface bedrock near Ithaca, NY?

3) Define radioactive decay:

The breakdown of an unstable atom into a more stable atom which is a completely different element.

5) Parts of radioactive decay

Parent isotopeThe unstable

isotopeDecreases during

decay

Daughter isotopeThe stable isotope Increases during decayA.k.a. decay product

C-14 N-14

5) Define half life: It is the time needed for half of a substance to decay into its stable form.

6) Why is the half life so useful for accurate dating?Nothing can change the half life.

7) Which isotope should we use?

Carbon- 14Short half-lifeDates living thingsRecent events of less than 50,000

years (Pleistocene to Holocene)

Potassium-40Looooong half-lifeCan be used on rocksDates very old events

# of half-lives

# of years passed

fraction remaining

amount of C-14

amount of N-14

0        

1        

2        

3        

4        

0 1/1 100g 0g5,700 1/2 50g 50g11,400 1/4 25g 75g17,100 1/8 12.5g87.5g22,800 1/166.25g93.75g

Carbon-14

Nitrogen-14

How old is a substance that has 100g of Carbon-14 and 100 g of Nitrogen-14?

How old is a fossil that contains 25g of Potassium-40 and 175 g of Argon-40?

One half life

5,700 years old

Three half lives3.9 x 109 years old