Ch. 21 Sec. 4

1. Ch. 21 Sec. 4 Fossil Remains

2. Fossils provide scientists with a record of the history of life on Earth. Vocabulary groundwater: water beneath Earth’s surface

3. I. The Fossil Record • Fossils – preserved remains or traces of once living organisms • 1. provide evidence of the past • 2. variety life-forms most now extinct • 3. evidence that species have evolved • B. Evolution - change in a species over time

4. C. Fossil correlation – rocks are about the same age as the fossils, and they can infer that the same fossils found elsewhere are also of the same age 1. Past climates & environments 2. Radiolarians (microfossils) a. Radiolarian ooze b. Petroleum

5. D. Original preservation 1. Remains of plants and animals that have been altered very little since the organisms’ deaths a. uncommon b. freezing c. arid d. oxygen-free environments

6. E. Altered hard parts Under most circumstances, the soft organic material of plants and animals decays quickly. Over time, the remaining hard parts, such as shells, bones, or cell walls, can become fossils with altered hard parts.

7. Altered hard parts In the process of mineral replacement, the pore spaces of an organism’s buried hard parts are filled in with minerals from groundwater.

8. Altered hard parts Recrystallization can occur when a buried hard part is subjected to changes in temperature and pressure over time. The original mineral is transformed into a new mineral.

9. F. Molds and casts A mold forms when sediments cover the original hard part of an organism, such as a shell, and the hard part is later removed by erosion or weathering. A mold might later become filled with a material to create a castof the shell.

10. G. Trace fossils Sometimes the only fossil evidence of an organism is indirect. Indirect fossils, called trace fossils, include traces of worm trails, footprints, and tunneling burrows. Trace fossils can provide information about how an organism lived, moved, and obtained food.

11. Some examples of trace fossils Dinosaur tracks Coprolites Gastroliths

12. II. Index Fossils • Easily recognized • Abundant • Widely distributed geographically • Represent species that existed for relatively short periods of geologic time

13. These trilobite species make excellent index fossils for the Paleozoic Era because each species lived for a relatively short period of time before becoming extinct. Fig. 21.25 Page 609

14. What is an index fossil? Answer: Index fossils are those that are easily recognized, abundant, widespread, and represent a species that existed for a relatively short period of time. Such fossils can be used to determine the approximate age of the rocks in which they are found.

15. Fossils provide scientists with a record of the history of life on Earth. • Fossils provide evidence that species have evolved. • Fossils help scientists date rocks and locate reserves of oil and gas.

16. Fossils can be preserved in several different ways. • Index fossils help scientists correlate rock layers in the geologic record.