5-2 The Fossil Record

1. 5-2 The Fossil Record http://www.kpbsd.k12.ak.us/chapman/demers/images/collage2.JPG

2. What is a fossil? • Some of the most important clues to Earth’s past are fossils. • A fossil is the preserved remains or traces of an organism that lived in the past. • Most fossils form when organisms that die become buried in sediments (particles of soil and rock).

3. Why are fossils important? • It enabled scientists to see occurrence of extinction in different species • It gave Darwin evidence that earth is older than previously believed and that very slow changes over a long period of time can add up to substantial changes in organisms • It shows evidence of continental drift – the belief that the continents were once one large landmass

4. Plummer et al 2003

5. Fossilization • Hard parts of organisms are more likely to be preserve than soft parts. • Soft parts are likely to decay or be consumed by other organisms • Because of this soft bodied creatures such as jellyfish may not be fossilized either • Buried organisms are more likely to be fossilized because it minimizes the decay, consumption, and destruction of the remains

6. Types of Fossils • Petrified Fossils – remains that become buried in sediments and actually changed to rock. • Mold – a hollow space in sediment in the shape of an organism or part of an organism • Cast – copy of the shape of the organism that made the mold • Preserved Remains – entire organisms kept intact in ice, tar, or amber • Traces – other evidence that an organism existed, ex. tracks, trails, footprints

7. Preserved Remains Petrified Fossils http://www.fp.sfasu.edu/geology/GeologyTutorial/Fossils/CARBONization01.JPG http://www.fossilmall.com/Stonerelic/amber/a25/bazaar_hemipteran_a25.htm Impression - Cast and Mold http://gpc.edu/~pgore/myphotos/fossils/cast&mold.jpg

8. Petrified wood Trace fossil http://www.clas.ufl.edu/users/pciesiel/gly3603c/wood1.jpg http://www.dinosaursrock.com/SteveDiloposaurusFootPrint.jpg

9. Age on Earth • Scientists can determine a fossils age in two ways: • relative dating: used to determine which of two rocks is older (layers at the top of the rock are younger than layers at the bottom) • Absolute dating : used to determine the actual age of fossils

10. Fossil Record • The millions of fossils that scientists have collected • A species is extinct if no members of that species are still alive

11. Relative Dating Using Fossils http://www.carleton.ca/~tpatters/teaching/climatechange/rocks/rocks11.gif

12. Geologic Time Scale • A calendar of Earth’s history that spans over 4.6 billion years. • Scientists have divided this large time period into smaller units called eras and periods. • The largest span in the calendar is the Precambrian Era. • Very few fossils are found from the Precambrian Era

13. Plummer et al 2003 Also called Hadean

14. http://books.nap.edu/html/creationism/evidence.html

15. Theories of Evolution • Gradualism – evolution occurs slowly but steadily • Punctuated equilibria – species evolve during short periods of rapid change