Transcript 7-2 Notes - power point

7-2 Notes
Absolute Ages of Rocks
Chapter 7, Lesson 2
What is Earth’s Age?
• Scientists discovered and used a natural
“clock” to date the age of Earth,
meteorites, and the moon.
What is Earth’s Age?
• Scientists used this
natural clock to
determine the age of
bog bodies.
The Tollund Man is the
naturally mummified corpse
of a man who lived during
the 4th century BCE.
The Lindow Man has
been Carbon-14 dated
to sometime between 2
BCE and 119 CE
Atoms and Isotopes
• Atoms are the microscopic building blocks
of all matter on Earth.
Atoms and Isotopes
• Atoms have 3 small parts:
– protons (positive charge) and neutrons (no
charge) are located in the nucleus (center)
– electrons (negative charge) orbit in clouds
around the nucleus
Atoms and Isotopes
• An element is defined by the number of
protons it has (listed as the atomic number
on the periodic table).
Carbon’s atomic number is 6.
It has 6 protons.
Atoms and Isotopes
• An isotope is when atoms of an element
have the same number of protons, but
differing number of neutrons.
Atoms and Isotopes
• Normal carbon is called carbon-12 and it
has 6 neutrons.
• Carbon isotopes:
– carbon-13 has 7 neutrons
– carbon-14 has 8 neutrons
Atoms and Isotopes
Atoms and Isotopes
Atoms and Isotopes
• Isotopes may be stable or unstable.
• When they are unstable, they are called
radioactive, and they can’t keep
themselves together – they decay.
Radioactive Decay
Atoms and Isotopes
• Radioactive decay occurs when an
unstable nucleus changes into another
nucleus by emitting particles and energy.
Atoms and Isotopes
• The isotope that undergoes radioactive
decay is the parent isotope.
• The stable form of the element that forms
is the daughter isotope.
Parent
Daughter
Atoms and Isotopes
• This decay is the natural clock that
scientists use to find the ages of Earth’s
rocks.
Atoms and Isotopes
• Parent isotopes decay into daughter
isotopes at a constant rate called the
decay rate.
Atoms and Isotopes
Atoms and Isotopes
• The half-life of an
element is the
calculated length of
time it takes for
half a specific
amount of a parent
isotope to decay.
Atoms and Isotopes
• Half-life of the carbon-14 isotope:
1/1 at
start
1/2 left
after
5730
years
1/4 left
after
another
5730
years
1/8 left
after
another
5730
years
Atoms and Isotopes
Radiometric Dating
• Scientists use radiometric dating to
calculate absolute ages of rocks and
minerals.
Radiometric Dating
– Comparing the
amount of parent to
daughter material
determines the
number of half-lives
the material has
been through.
Radiometric Dating
– Igneous rock is most commonly used for
radiometric dating because it came from
melted rock, which “resets” its natural clock.
Radiometric Dating
Radiometric Dating
Radiometric Dating
• Rock grains from continental shields,
where the oldest rocks on Earth occur, are
estimated to be 4.0 to 4.4 billion years old.
Radiometric Dating
About 4.5 billion years ago, there is
evidence that a rogue planet,
Orpheus/Theia collided with Earth and
formed our moon. This reset the age of
many of Earth’s rocks.
Radiometric Dating
• Scientists used radiometric dating to
determine the ages of meteorites and the
Moon.
Radiometric Dating
• The ages of meteorites recently collected
in Antarctica are 4.5 - 4.6 billion years old.
Radiometric Dating
• The ages of rocks collected from the moon
are about 4.6 billion years old.
Radiometric Dating
• Earth is approximately 4.6 billion years
old.
Radiometric Dating
50% of Americans believe the UNIVERSE
is less than 10,000 years old…
Radiometric Dating
That would mean the universe began
AFTER the domestication of the dog…?
Radiometric Dating
• The closeness of calculated ages of Earth,
the Moon, and meteorites helps confirm
that the entire solar system formed at the
same time.
7.2 Absolute Ages of Rocks
1.
2.
3.
4.
A
B
C
D
The isotopes of an element have a
different number of what?
A protons
B neutrons
C electrons
D atoms
7.2 Absolute Ages of Rocks
1.
2.
3.
4.
A
B
C
D
What important feature of radioactive decay
has allowed geologists to date rocks?
A the isotopes of an element may be stable
or unstable
B the nucleus gains or loses protons
C parent isotopes decay into daughter
isotopes
D the decay occurs at a constant rate
7.2 Absolute Ages of Rocks
1.
2.
3.
4.
A
B
C
D
What do scientists use to measure
the absolute age of a rock?
A radiometric dating
B amount of carbon in the rock
C absolute dating
D relative dating
1.
2.
3.
4.
A
B
C
D
What type of rock is most commonly
used in radiometric dating?
A metamorphic
B igneous
C sedimentary
D minerals
1.
2.
3.
4.
A
B
C
D
Which type of rock is the most
useful for relative dating?
A igneous
B sedimentary
C magma
D metamorphic
1.
2.
3.
4.
A
B
C
D
What term describes time it takes for
a sample of a radioactive isotope to
decay to half its original mass?
A absolute age
B half-life
C radiometric dating
D relative age
1.
2.
3.
4.
A
B
C
D
Which describes a daughter isotope?
A decays into a parent isotope
B is an unstable form of the parent
isotope
C is the result of parent isotope decay
D is heavier than its parent isotope
1.
2.
3.
4.
A
B
C
D
What percentage of parent isotope
remains after 2 half-lives?
A 75%
B 30%
C 37.5%
D 25%
1.
2.
3.
4.
A
B
C
D
Which best describes the relationship
between the ages of the Earth and the
Moon?
A They are about the same age.
B Earth is much older than the moon.
C The moon is much older than Earth.
D Earth is much younger than the
moon.
1.
2.
3.
4.
A
B
C
D
Scientists believe that the Earth is
about ___ billion years old.
A 7.3
B 2.2
C 3.5
D 4.6
Natural Phenomena - Rocks Fossils and Earth History (15:05)