L7 - How Old Is the Earth? Flashcards

1
Q

Who was the first person to try and date the Earth, what were his methods and what number did he come up with?

A
  • James Ussher, 1654
  • BibHule
  • 4004BC
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2
Q

Who was the second person to try and date the Earth, what were his methods and what number did he come up with?

A
  • Nicolaus Steno, 1638-86
  • Shark teeth
  • None in particular but evidence the world had changed
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3
Q

Who was the third person to try and date the Earth, what were his methods and what number did he come up with?

A
  • Compte de Buffon, 1778
  • Cooling ball of metal
  • 75,000yrs
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4
Q

Who was the fourth person to try and date the Earth, what were his methods and what number did he come up with?

A
  • James Hutton
  • Uniformitarianism
  • No definitive age, just very very old
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5
Q

What are the four principles of uniformitarianism?

A

Superposition
Original Horizontality
Cross-cutting relationships
Unconformities

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6
Q

Give an example of uniformitarianism

A

Sand ripples on a beach today is observable in sandstone from 1000s of years ago

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7
Q

Why might uniformitarianism not hold true?

A

Species and climates can change radicallly, with no analogues in modern day

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8
Q

How is relative dating different from absolute dating of rock layers?

A

You can say that rock X is older than rock Y without actually knowing the age of either through principles of uniformitarianism.

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9
Q

Explain superposition

A

Newer layers layered on top of older ones

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10
Q

Explain original horizontality

A

Layers are laid down horizontally

Sediment rarely accumulates on a slope

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11
Q

Explain cross-cutting relationships

A

Younger features will truncate older features

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12
Q

Explain unconformities

A

Unconformities (where two layers of rock are radically different) tend to represent huge gulfs in time. With the rocks above the unconformity beinng significantly older than those below.

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13
Q

Who was the fifth person to try and date the Earth and what number did he come up with?

A

John Joly, late 19th century

90 million years

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14
Q

Who was the sixth person to try and date the Earth and what number did he come up with?

A

Lord Kelvin, late 19th century

20-30 million years

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15
Q

How did we uncover the real age of the Earth

A

Radiometric dating

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16
Q

How does radiometric dating work?

A

By measuring amount of ‘daughter atoms’ in a mineral and thus, using pre-existing knowledge of the half-life of the element, ‘counting-back’ to find the age of the material.

17
Q

State the name and origin of the world oldest rock

A

Acasta Gneiss, Canada