Question

Scientists estimate Earth's age to be 4.6 billion years. Samarium has a half-life of approximately 106 billion years. From the present date, approximately how many more years must pass before a sample of samarium that was created at the beginning of Earth's history contains 50 percent of the original parent material? 1 billion 10 billion 100 billion 1,000 billion

Answer 1

100 billion (approximately). If a samarium sample was created at the beginning of Earth's history, that would put it at the same age as earth (4.6 billion years). If samarium's half life is 106 billion years, and 4.6 billion years have already passed, then 106 billion - 4.6 billion leaves you with 101.4 billion years left till it's half life (rounds closest to 100 billion years from answer choices).