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7-2 Notes Absolute Ages of Rocks Chapter 7, Lesson 2

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What is Earths Age? Scientists discovered and used a natural clock to date the age of Earth, meteorites, and the moon.

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What is Earths Age? Scientists used this natural clock to determine the age of bog bodies. The Lindow Man has been Carbon-14 dated to sometime between 2 BCE and 119 CE The Tollund Man is the naturally mummified corpse of a man who lived during the 4 th century BCE.

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Atoms and Isotopes Atoms are the microscopic building blocks of all matter on Earth.

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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

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Atoms and Isotopes An element is defined by the number of protons it has (listed as the atomic number on the periodic table). Carbons atomic number is 6. It has 6 protons.

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Atoms 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 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 Isotopes

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Isotopes may be stable or unstable. When they are unstable, they are called radioactive, and they cant keep themselves together – they decay. Radioactive Decay

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Atoms and Isotopes Radioactive decay occurs when an unstable nucleus changes into another nucleus by emitting particles and energy.

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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

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Atoms and Isotopes This decay is the natural clock that scientists use to find the ages of Earths rocks.

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Atoms and Isotopes Parent isotopes decay into daughter isotopes at a constant rate called the decay rate.

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Atoms and Isotopes

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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 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

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Atoms and Isotopes

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Radiometric Dating Scientists use radiometric dating to calculate absolute ages of rocks and minerals.

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Radiometric 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 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 Dating

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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 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 Earths rocks.

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Radiometric Dating Scientists used radiometric dating to determine the ages of meteorites and the Moon.

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Radiometric Dating The ages of meteorites recently collected in Antarctica are 4.5 - 4.6 billion years old.

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Radiometric Dating The ages of rocks collected from the moon are about 4.6 billion years old.

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Radiometric Dating Earth is approximately 4.6 billion years old.

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Radiometric Dating 50% of Americans believe the UNIVERSE is less than 10,000 years old…

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Radiometric Dating That would mean the universe began AFTER the domestication of the dog…?

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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.

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The isotopes of an element have a different number of what? Aprotons Bneutrons Celectrons Datoms 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? Athe isotopes of an element may be stable or unstable Bthe nucleus gains or loses protons Cparent isotopes decay into daughter isotopes Dthe 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? Aradiometric dating Bamount of carbon in the rock Cabsolute dating Drelative 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? Ametamorphic Bigneous Csedimentary Dminerals 1.A 2.B 3.C 4.D

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Which type of rock is the most useful for relative dating? Aigneous Bsedimentary Cmagma Dmetamorphic 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? Aabsolute age Bhalf-life Cradiometric dating Drelative age 1.A 2.B 3.C 4.D

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Which describes a daughter isotope? Adecays into a parent isotope Bis an unstable form of the parent isotope Cis the result of parent isotope decay Dis 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? A75% B30% C37.5% D25% 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? AThey are about the same age. BEarth is much older than the moon. CThe moon is much older than Earth. DEarth 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. A7.3 B2.2 C3.5 D4.6 1.A 2.B 3.C 4.D

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