Reading the Layers: teacher key

Fossils, grade 8 edition, written for 8th grade. Rock layers hold a record of life in a known order. Read how that order, William Smith, index fossils and radioactive clocks let geologists date rock, and what Tiktaalik and Archaeopteryx show.

Read the book. Print this page for the key.

Questions and answers

1. What does the principle of faunal succession say each layer of rock holds?
   • Only sea fossils
   • The age of the Earth
   • Its own record of life (answer)
2. In an undisturbed stack of rock layers, fossil A lies two layers below fossil B, and fossil C lies one layer above B. Which fossil is the oldest?
   • Fossil B
   • Fossil A (answer)
   • Fossil C
3. Why do the radioactive atoms in some rocks work like a clock?
   • They break down at a steady, constant rate (answer)
   • They glow at night
   • They move up through the layers
4. What does the word anatomist mean in 'Georges Cuvier, a French anatomist'?
   • A person who maps mountains
   • A person who drives a boat
   • A person who studies the body of living things (answer)
5. Why do sea fossils sit high in some mountains?
   • Slow movements of Earth's crust pushed old sea floor up (answer)
   • The sea once covered the mountain tops
   • Animals climbed them

Words

• faunal: about animals
• succession: coming in order
• radiometric: using radioactive clocks
• anatomist: body expert
• limestone: kind of rock