1. 5-2 The Fossil Record

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. Impression - Cast and Mold
Preserved Remains
Petrified Fossils
Impression - Cast and Mold

8. Petrified wood Trace fossil

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

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

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