Lab 4: Determining When Dinosaurs Lived

Question 1

Radio active Na-24 decays with a half life of 15 hours. Starting with 1000 atoms of Na-24, how many atoms would be left after 45 hours?

Answer 1

0 hours= 1000Parent atoms and 0 Daughter atoms

15 hours=500 parent atoms and 500 daughter atoms

30hours= 250parent atoms (500 halfed) 750 daughter atoms (500+250)

45 hours= 125 parent atoms, 875 daughter atoms

Question 2

An igneous rock is analyized and found to have 22865 atoms of U-235 (704 million years) and 4070 of Pb-207. How old is the rock?

Answer 2

thl= 704 million
N=22865
N0= 26935 (N0 + years)

t= 166.4 million years

Question 3

How many half lives are required to yeild a mineral with 300 atoms of Th-232 and 38140 atoms of Pb-208 (14.1 billion years)

Answer 3

thl= 14.1 billion
N=300
N0= 38440 (300+38140)

t=98.7 billion years
98.7 divided 14.1=7 half lives

Question 4

t

Answer 4

age of the material

Question 5

thl

Answer 5

length of half life for parent-daughter pair

Question 6

N

Answer 6

amount of parent material measured after decay

Question 7

N0

Answer 7

original amount of parent material before decay

Question 8

N0=N+D

Answer 8

D= current amount of daughter material after decay

Question 9

fundemental geological princeples (6) and explain them

Answer 9

1. original horizontality- sediments are deposited in flat horizontal layers, not angles
2. superposition- oldest sediment is buried lower than younger sediment
3. lateral continuity- same layers on both sides. If you go dino digging you will find fossils lateral to eachother not on top or below
4. cross cutting- the sediment that cuts across is the younger sediment, something must be there already for it to cut through
5. inclusions- younger rock can be in older rock
6. unconformities- layers can be lost due to erosion