Transcript The Geosphere

Unit 6 – The Geosphere
Vocabulary
1.
2.
3.
4.
Uniformitarianism
Relative Dating
Law of Superposition
Principle of Original
Horizontality
5. Principle of CrossCutting Relationships
6. Unconformity
7. Correlation
8.
9.
10.
11.
12.
13.
14.
Fossil
Index Fossil
Radioactivity
Half Life
Radiometric Dating
Radiocarbon Dating
Geologic Time Scale
Discovering Earth’s History
Rocks Record Earth’s History
1. Rocks record geological events and
changing life forms of the past.
2. Scientists have learned that the Earth
is much older than previously thought
and the Earth’s surface and interior
have been changed by the same
geological processes that go on today.
A Brief History of Geology
1. In the mid 1600’s
James Ussher
made a timeline of
both human and
Earth history and
determined the
Earth was more
than 5,000 years
old.
2. In the late 1700’s,
James Hutton, a
Scottish physician,
published a book
called Theory of the
Earth and
established the
principle of
uniformitarianism.
 Uniformitarianism means that the forces
and processes that have shaped Earth in
the past are essentially the same as those
operating today.
Relative Dating - Key Principles
1. Relative dating is a
process by which rocks
are placed in their
proper sequence or
order. Only the
chronological order of
events are determined,
not the absolute age in
years.
2. Nicolaus Steno
proposed the Law of
Superposition which
states in an
undeformed sequence
of sedimentary rocks,
each layer is older
than the one above it
and younger than the
layer below it.
A
Youngest
B
C
D
Oldest
3. Steno also posed
the Principle of
Original
Horizontality
which says the
layers of sediment
are generally
deposited in a
horizontal position.
4. The Principle of
Cross-Cutting
Relationships
states that a rock
or fault is
younger than any
rock or fault
through which it
cuts.
5. No place on Earth is
geologically
complete.
Unconformities are
surfaces that
represent a break in
the rock record,
caused by erosion or
lack of deposition.
The Great Unconformity
Correlation of Rock Layers
1. To develop a geologic time scale
that can be applied to the entire
Earth, rocks of similar age in
different regions must be matched
up- a task called correlation.
2. By correlating rocks, it is
possible to create a more complete
view of the geologic history of the
region.
Relative Ages of Rocks WS
A
Can you find the man in the beans?
Dating With Radioactivity
• Basic Atomic Structure
o There are protons and neutrons in an atom’s
nucleus.
o The number of neutrons in an atom can vary these are called isotopes.
• Radioactivity
o When nuclei are unstable, they break apart, or
decay, in a process known as radioactivity.
o An unstable or radioactive isotope is
called a parent.
o The isotopes that result from the decay
of the parent are called daughter
products.
• Half-Life
o A half-life is a common way of expressing
the rate of radioactive decay.
o A half-life is the time required for one half
of the atoms of a radioactive substance
to decay.
Say what!?!?
• A 100g sample of Borchiksonium has a
half-life of 5 years.
o After 5 years - 50 grams remain
o After 10 years - 25 grams remain
o After 15 years - 12.5 grams remain
o After 20 years - 6.25 grams remain
• Radiometric Dating
o Radiometric dating is the procedure of
calculating the absolute ages of rocks
and minerals that contain radioactive
isotopes.
• Dating with Carbon-14
o Radiocarbon dating is the method for
determining age by comparing the
amount of Carbon-14 to the amount of
Carbon-12 in a sample.
So what!
• Importance of Radiometric Dating
o Radiometric dating has been used to date
thousands of events in Earth’s history.
o Rocks on Earth have been dated to be as
much as 4 billion years old.