L7 - How Old Is the Earth? Flashcards
Who was the first person to try and date the Earth, what were his methods and what number did he come up with?
- James Ussher, 1654
- BibHule
- 4004BC
Who was the second person to try and date the Earth, what were his methods and what number did he come up with?
- Nicolaus Steno, 1638-86
- Shark teeth
- None in particular but evidence the world had changed
Who was the third person to try and date the Earth, what were his methods and what number did he come up with?
- Compte de Buffon, 1778
- Cooling ball of metal
- 75,000yrs
Who was the fourth person to try and date the Earth, what were his methods and what number did he come up with?
- James Hutton
- Uniformitarianism
- No definitive age, just very very old
What are the four principles of uniformitarianism?
Superposition
Original Horizontality
Cross-cutting relationships
Unconformities
Give an example of uniformitarianism
Sand ripples on a beach today is observable in sandstone from 1000s of years ago
Why might uniformitarianism not hold true?
Species and climates can change radicallly, with no analogues in modern day
How is relative dating different from absolute dating of rock layers?
You can say that rock X is older than rock Y without actually knowing the age of either through principles of uniformitarianism.
Explain superposition
Newer layers layered on top of older ones
Explain original horizontality
Layers are laid down horizontally
Sediment rarely accumulates on a slope
Explain cross-cutting relationships
Younger features will truncate older features
Explain unconformities
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.
Who was the fifth person to try and date the Earth and what number did he come up with?
John Joly, late 19th century
90 million years
Who was the sixth person to try and date the Earth and what number did he come up with?
Lord Kelvin, late 19th century
20-30 million years
How did we uncover the real age of the Earth
Radiometric dating