Feb_14 - How Old Are Planets Stars Thursday February 14"How...

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How Old Are Planets How Old Are Planets Thursday, February 14 Thursday, February 14
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“How old is the Earth?” This question has been asked repeatedly throughout human history.
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Before the 18 th century, biblical chronology biblical chronology was the accepted method of finding the Earth’s age. St. Augustine: Earth created 5500 BC J. Kepler: Earth created 3993 BC Isaac Newton: Earth created 3998 BC
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The ultimate in precision: in the 17th century, Archbishop James Ussher wrote: “The beginning of time…fell on the beginning of the night which preceded the 23 rd day of October, in the year 4004 BC.”
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Hinduism: Cycle of creation and destruction. “Day of Brahma” = 4.32 billion years. Jainism: “Know that the world is uncreated, as time itself is, without beginning or end.” Buddhism: “Many statements I have left unsaid. Why have I left them unsaid? Because they are not helpful.”
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18 th century: Geologists realized that the Earth is much more than 6000 years old. The White Cliffs of Dover: a layer of tiny shells, 100 meters thick. A huge number & variety of fossils on Earth (> 99.9% of all species are extinct).
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Thick layers of sedimentary rock, deeply eroded canyons. Grand Canyon
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Edmund Halley: Oceans become saltier with time, as rivers wash salt into the sea. The Earth is not very young (oceans would be fresh water). The Earth is not infinitely old (oceans would be saturated with salt).
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rocks: Radioactive dating Radioactive dating Some atomic nuclei are unstable. They undergo
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This note was uploaded on 07/17/2008 for the course ASTRO 294 taught by Professor Ryden during the Winter '08 term at Ohio State.

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Feb_14 - How Old Are Planets Stars Thursday February 14"How...

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