Exit Ticket - Radioactive Dating

What method do scientists most often use in determining the absolute age of fossils and rock layers of the Earth?

• comparing the amount of uranium remaining and the amount of lead formed in radioactive dating of rock layers

• counting the number of sedimentary rock layers in the Earth’s crust

• observing folds, plate shifting, and unconformities in rock layers

• using index fossils to determine the age of rock layers

Rock layers were found containing 30 kg of radioactive elements that had a half life of 5 million years. How old were the rock layers if scientists determined that the samples had originally contained 120 kg of the radioactive materials?

• 5 million years old

• 10 million years old

• 15 million years old

• 20 million years old

Scientists are analyzing a recently unearthed fossil using radiometric dating techniques. Twenty-five percent of the original uranium-235 in the sample has decayed into lead-207. Scientists determine that the fossil is MOST likely from which Paleozoic period?

• Permian

• Carboniferous

• Silurian

• Cambrian