1. Geologic Time
Page 29 of INB

2. EQ:
What evidence supports the theory the Earth is very old?

3. Theories of time. Rock layering takes time, so, Earth must be old.
As sediment builds rocks are formed, oldest on bottom.
Only gives a relative age of rocks
Critters and plants buried in the sediment can become fossils

4. Radioactive Decay
Some elements are unstable and breakdown
Parent  Daughter
Decay happens at a constant rate called half-life
If we know the rate of decay we can calculate the age of the rock.

6. Geologic time scales
Oldest rocks are on the bottom, so, oldest time on the bottom
Divided into Eons, Eras, Periods, Epochs
Not a set period of time between each, but a major change in the fossils

7. If the history of the Earth was 1 year
Jan 1 12:00 am Earth was formed
2/21 first organism
11/20 first organism crawled onto land
12/25 dinosaurs arrive
12/31 afternoon first human primates arrive

8. YOUNGEST
500 MYA
OLDEST