Earth Science Regents Review
Unit 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?

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 Ash
Useful 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
7
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.Phacops
2.condor
3.Coelophysis
4.Tetragraptus
Which fossil may be found in the
surface bedrock near Ithaca, NY?
1.
2.
3.
4.
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 isotope
Daughter isotope


The unstable
isotope
 Decreases during
decay
The stable isotope
 Increases during
decay
 A.k.a. decay product
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- 14
Potassium-40


Short half-life
 Dates living things
 Recent events of
less than 50,000
years (Pleistocene
to Holocene)
Looooong half-life
 Can be used on
rocks
 Dates very old
events
# of half- # of years
passed
lives
0
1
2
3
4
fraction
remaining
amount of
C-14
amount of
N-14
 How
old is a
 How old is a fossil that
substance that has
contains 25g of
100g of Carbon-14
Potassium-40 and
and 100 g of Nitrogen- 175 g of Argon-40?
14?