7-2 notes absolute ages of rocks chapter 7, lesson 2
TRANSCRIPT
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7-2 Notes 7-2 Notes Absolute Ages of RocksAbsolute Ages of Rocks
Chapter 7, Lesson 2Chapter 7, Lesson 2
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What is Earth’s Age?What is Earth’s Age?
• Scientists discovered and used a natural “clock” to date the age of Earth, meteorites, and the moon.
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What is Earth’s Age?What is Earth’s Age?• Scientists used this
natural clock to determine the age of bog bodies.
The Lindow Man has The Lindow Man has been Carbon-14 dated been Carbon-14 dated to sometime between 2 to sometime between 2 BCE and 119 CEBCE and 119 CE
The Tollund Man is the The Tollund Man is the naturally mummified corpse naturally mummified corpse of a man who lived during of a man who lived during the 4the 4thth century BCE. century BCE.
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Atoms and IsotopesAtoms and Isotopes
• Atoms are the microscopic building blocks of all matter on Earth.
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Atoms and IsotopesAtoms 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
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Atoms and IsotopesAtoms 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.
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Atoms and IsotopesAtoms and Isotopes
• An isotope is when atoms of an element have the same number of protons, but differing number of neutrons.
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Atoms and IsotopesAtoms 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
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Atoms and IsotopesAtoms and Isotopes
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Atoms and IsotopesAtoms and Isotopes
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Atoms and IsotopesAtoms 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
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Atoms and IsotopesAtoms and Isotopes
• Radioactive decay occurs when an unstable nucleus changes into another nucleus by emitting particles and energy.
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Atoms and IsotopesAtoms 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
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Atoms and IsotopesAtoms and Isotopes
• This decay is the natural clock that scientists use to find the ages of Earth’s rocks.
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Atoms and IsotopesAtoms and Isotopes
• Parent isotopes decay into daughter isotopes at a constant rate called the decay rate.
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Atoms and IsotopesAtoms and Isotopes
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Atoms and IsotopesAtoms 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.
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Atoms and IsotopesAtoms and Isotopes
• Half-life of the carbon-14 isotope:
1/1 at start
1/2 leftafter5730years
1/4 leftafter
another5730years
1/8 leftafter
another5730years
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Atoms and IsotopesAtoms and Isotopes
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Radiometric DatingRadiometric Dating
• Scientists use radiometric dating to calculate absolute ages of rocks and minerals.
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Radiometric DatingRadiometric Dating
– Comparing the amount of parent to daughter material determines the number of half-lives the material has been through.
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Radiometric DatingRadiometric Dating
– Igneous rock is most commonly used for radiometric dating because it came from melted rock, which “resets” its natural clock.
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Radiometric DatingRadiometric Dating
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Radiometric DatingRadiometric 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.
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Radiometric DatingRadiometric DatingAbout 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.
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Radiometric DatingRadiometric Dating
• Scientists used radiometric dating to determine the ages of meteorites and the Moon.
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Radiometric DatingRadiometric Dating
• The ages of meteorites recently collected in Antarctica are 4.5 - 4.6 billion years old.
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Radiometric DatingRadiometric Dating
• The ages of rocks collected from the moon are about 4.6 billion years old.
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Radiometric DatingRadiometric Dating
• Earth is approximately 4.6 billion years old.
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Radiometric DatingRadiometric Dating
50% of Americans believe the UNIVERSE is less than 10,000 years old…
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Radiometric DatingRadiometric Dating
That would mean the universe began AFTER the domestication of the dog…?
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Radiometric DatingRadiometric Dating
• The closeness of calculated ages of Earth, the Moon, and meteorites helps confirm that the entire solar system formed at the same time.
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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. A
2. B
3. C
4. D
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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. A
2. B
3. C
4. D
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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
7.2 Absolute Ages of Rocks
1. A
2. B
3. C
4. D
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What type of rock is most commonly used in radiometric dating?
A metamorphic
B igneous
C sedimentary
D minerals
1. A
2. B
3. C
4. D
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Which type of rock is the most useful for relative dating?
A igneous
B sedimentary
C magma
D metamorphic
1. A
2. B
3. C
4. D
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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. A
2. B
3. C
4. D
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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. A
2. B
3. C
4. D
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What percentage of parent isotope remains after 2 half-lives?
A 75%
B 30%
C 37.5%
D 25%
1. A
2. B
3. C
4. D
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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. A
2. B
3. C
4. D
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Scientists believe that the Earth is about ___ billion years old.
A 7.3
B 2.2
C 3.5
D 4.6
1. A
2. B
3. C
4. D