Question

Rank the following meteorites in terms of their age, from youngest to oldest:1) a meteorite containing 500 238U isotopes and 100 206Pb isotopes.2) a meteorite containing 400 238U isotopes and 100 206Pb isotopes.3) a meteorite containing 400,000 238U isotopes and 400,000 206Pb isotopes.4) a meteorite containing 4,000 238U isotopes and 200 206Pb isotopes.5) a meteorite containing 3,000 238U isotopes and 1,000 206Pb isotopes.

Answer 1

Answer:

Explanation:

When 238U which is radioactive turns into 206Pb , it becomes stable and no further disintegration is done . Hence in the initial period ratio of 238U undecayed and 206Pb formed  will be very high because no of atoms of 238U in the beginning will be very high. Gradually number of 238U undecayed will go down and number of 206Pb formed will go up . In this way the ratio of 238U and 206Pb in the mixture will gradually reduce to be equal to one or even less than one .

In the given option we shall calculate their raio

1 ) ratio of 238U and 206Pb = 5

2 ) ratio of 238U and 206Pb = 4

3 )ratio of 238U and 206Pb = 1

4 ) ratio of 238U and 206Pb = 20

5 )ratio of 238U and 206Pb = 3

lowest ratio is 1 , hence this sample will be oldest.

Ranking from youngest to oldest

4 , 1 , 2 , 5 , 3 .