Lunar rocks. You are dating Moon rocks based on their proportions of uranium-238 (half-life of about 4.5 billion years) and its ultimate decay product, lead. Find the age for the following
a. A rock for which you determine that 55% of the original uranium-238 remains, while the other 45% has decayed into lead.
.55 = (1/2)^(t / 4.5E9)
ln(5.5) = ln(1/2) * t / 4.5E9
[ln(.55) / ln(1/2)] * 4.5E9 = t
CONCLUSION: The rock is 3,881,230,000 years old.