| | Last lecture we looked at how the rock record was subdivided into the relative time units of the Geologic Time scale. |
| | Today we will look at how absolute dates were added to the Geologic Time scale |
| | There has been a long debate over the age of the Earth. |
| | The age of the earth is key to evalutating geologic and biologic processes. |
| | Uniformitarianism and Evolution require a large age of the Earth. |
| Measuring the age of the Earth |
| | extrapolating age by using generations listed in Genesis |
| | Bishop Jame Ussher (1665) |
| | El Moro Nation Monument, New Mexico |
| | Canyon De Chelly, Arizona |
| | Salt concentration in the oceans |
| | John Joly (1899), 90 million years |
| | John Phillips (1860), 96 Million years |
| | C.D Walcott (1893), 27.6 Million years |
| | Lord Kelvin (1862), 20 to 40 million years |
| | Radioactive Dating Methods |
| | Radioactivity discovered in 1890s |
| | Radioactive elements decay to non-radioactive forms at a constant rate |
| | Use uniformitarianism (present is key to past) |
| | Measure ratio of parent to daughter |
| | Half-lifes and Applicable Range |
| |
|
Parent
|
Daughter
|
Half-life
|
Applicable Range
|
|
Rubidium-87
|
Strontium
|
47,000 million years
|
> 10 million years
|
|
Thorium-232
|
Lead-208
|
13,900 million years
|
> 5 million years
|
|
Uranium-238
|
Lead-206
|
4,500 million years
|
> 1 million years
|
|
Uranium-235
|
Lead-207
|
713 million years
|
> 1 million years
|
|
Potassium
|
Argon
|
1,300 million years
|
>50,000 years
|
|
Carbon-14
|
Nitrogen-14
|
5,568 years
|
< 50,000 years
|
|
| | Oldest Earth rocks are 3.8 billion years old |
| | Meteorites on earth are generally around 4.6 billion years old |
| | Moon rocks are between 4.6 and 3 billion years old |
| | Age of the Earth is thought to be 4.6 billion years old |
|
