1. Lecture 4: Marine Fossils, geologic time scale
Corresponding Reading Material
~ Lab Manuel: Marine Fossils
~ Levinton:chapters 2 and 3

2. Evidence for Evolution
Similar life forms that are related
Vestigial traits and homologous characters
Evidence from the fossil record
~fossils are any trace of an organism that lived in the past.
Fact of extinction
Environmental change
Plate tectonics

3. Geological Time
Scientists have divided time since the formation of the Earth into a geological time scale.
Each period has characteristics or events that are unique to them.

4. How do we know the age of the Earth??
During Darwin’s time, the Earth was thought to be 6,000 years old. Why??
Moon rocks and meteorites
Theory of uniformitarianism states that geological process that are occurring today were the same in the past.

5. Relative vs Absolute Dating
Relative Dating = refers to the determination of the age of a rock or geological sample by comparing its position to the position of other samples.
Absolute Dating = refers to the determination of the age of a geological sample by calculations or radiometric decay and/or its position in relation to other samples

6. Dating Techniques
Radiometric Dating = the process of determining the age of rocks by observing the ratio of unstable radioactive elements to stable decay products
~ Half-life = is the time it takes for one half of all the unstable nuclei in a sample to decay. During this process the radioactive element becomes a new element.

7. Dating Techniques
Paleomagnetism = is the remnant magnetic field of a rock
~Tiny particles of iron-bearing minerals are present in
balsamic rocks
~ These particles align with the Earth's magnetic field at the
time they are formed and freeze in place as the rock
solidifies
~ In the last 26 mill yrs, the
poles have reversed 48 times.
~ This techniques is used to
calibrate the geological time
scale and to reconstruct
continents

8. Dating Technique

9. Dating Technique

10. How Are Fossils Made?
There are five ways an organism can become fossilized:
1. Permineralization (Petrification) = this process involves the replacement of the original organic tissues w/ minerals from the surrounding rock, including silica, calcite, or pyrite
2. Unaltered Preservation = occurs when the organism is preserved in its original state and is protected from the affects of permineralization (Ex: Insects which become trapped in tree sap which turns into amber)
3. Carbonization (Coalification) = results form the removal of all but the carbon elements (other elements such as hydrogen, oxygen, and nitrogen are removed)
Trilobite Fossil

11. How Are Fossils Made?
4. Authigenic Preservation = these fossils are mold and casts or organisms which have dissolved or rotted away, leaving only a trace of their existence (the parts of the organism that are replaced are usually the hard parts of the dead organism)
5. Recrystalization = occurs when crystals form within the original structure, eventually replacing it and resulting in a crystallized copy
Horn Coral Fossil
Brachiopod Fossil

12. Pictures of Fossils Sponge Fossil Eocene Fish Fossil
Ammonite Fossil (Jurassic Period)
Tuzoia Fossil

13. Fossils Over Time
Below the chart shows when different organisms appear within the fossil record.

14. Burgess Shale Fossil
The Burgess Shale is is an exceptional Middle Cambrian age (~540 mya) fossil locality located in Yoho National Park in the Rocky Mountains near Field, British Columbia, Canada.
It is special because of the soft-bodied preservation of a wide variety of fossil invertebrate animals.