Neptunium, a radioactive element has not been found to occur naturally on earth although it can be manufactured in the laboratory. Scientific literature sometimes uses this data to “prove” that the world must be very old, since if the earth were young, Neptunium should exist naturally. This argument sounds logical and has widespread acceptance.

According to *Evolutionary Cosmology* the moon is at least
as old as the earth (a believed 4.6 billion years). Therefore to be consistent,
Neptunium on the moon creates interesting problems for those who adhere to a
belief in an old age for the earth. We hope you can solve them! It is also a
useful assignment to hand out to the more mathematically inclined amongst grades
10, 11, or 12 science students when you are dealing with the age of the earth
and the solar system.

**Observation:** Neptunium is found on the moon. It is a radioactive
substance with a half life of 2.2 x 10^{6} years, i.e. in 2,200,000
years 1kg of Neptunium will decay to1/2kg Np plus other products.

**Question (1)** If Np is present on the moon, can the moon
be 4.6 x 10^{9} years old as commonly claimed?

Reasoning: (We’ve helped you a little—for Question 1, just fill in the space)

Believed age of moon=

1/2 life Np =

(Note: Most calculators will not handle this calculation. Use longhand method.)

**Now ask yourself:** “If all moon was pure NP originally,
(i.e. 46 billion years ago) how many grams of Np should be left in 1980” (Mass
moon = 8.3 x 10^{22}kg).

When you’ve worked this out you should be able to answer question 1.

**Question (2)** What would be the best argument against using
the Np on the moon as proof that the moon was young, i.e. could the Np have
another origin, i.e. meteoric bombardment, so that it is not part of the original
moon, etc. Explain your case in no more than 500 words.