You find the frozen remains of a woolly mammoth in an Alaskan glacier. You analyze a bit of the tusk and find that its 14C:12C ratio is about one-fourth (25%) of the baseline level typically found in living organisms. Given that the half-life of 14C is 5,730 years, when did the mammoth die?
A) 5,730 years ago
B) about 12,000 years ago
C) at least 25,000 years ago
D) about 75,000 years ago

Question

Quizplus · Accepted Answer

The decrease in the 14C:12C ratio to 25% of the baseline level indicates that half of the original 14C has decayed (since 0.5 = e^(-kt), where k is the decay constant and t is the time elapsed). Using the half-life of 5,730 years, we can calculate that two half-lives have passed (0.5^2 = 0.25), which corresponds to approximately 11,460 years. This means that the mammoth died about 12,000 years ago, which is consistent with the known extinction of woolly mammoths around that time. Choices A, C, and D are incorrect because they are either too recent or too distant in the past to account for the observed 14C:12C ratio.

You Find the Frozen Remains of a Woolly Mammoth in an Alaskan