1. 17-1 The Fossil Record

2. A fossil is defined as any evidence of life that existed long ago. A fossil can be a plant, an animal, a footprint, an egg, a carbon signature, etc. More than 99% of every species that has ever appeared on Earth have gone extinct.

3. Fossils form when an organism dies and is buried by sedimentary rock. As the rock layers deepen, the pressure, moisture, and chemical activities turn an organism’s remains to rock. Conditions have to be perfect for a fossil to form.

4. Copyright Pearson Prentice Hall How Fossils Form Fossil Formation Water carries small rock particles to lakes and seas.

5. Copyright Pearson Prentice Hall How Fossils Form Dead organisms are buried by layers of sediment, which forms new rock.

6. How Fossils Form The preserved remains may be later discovered and studied.

7. Trilobite (Asaphus kowalewskii) – Ordovician Period

8. Ginkgo biloba – Living fossil

9. Fossils are interpreted in two ways: 1.Relative dating determines the age of a fossil by comparing the rock it’s formed in to neighboring layers of rock. Index fossils are those that are created from an easily recognized species that existed for a short period of time over a wide geographic range.

10. Index Fossils

11. 2. Radioactive dating involves measuring the amount of radioactive isotopes in samples of rock. The half-life is the length of time for half of these atoms to decay.

12. Evolutionary time can be represented in geologic time scales. Each major time span is divided into eras, then eras are subdivided into periods. Study the three eras (p.421), know their order and roughly what life appeared in each.

13. Exit Slip Many more types of fossils have been found since Darwin’s day, allowing several gaps in the fossil record to be filled. How might this information make relative dating more accurate?