1. Ch. 15 Evolution Fossil · Trace of a long dead organism
· There are 3 types of fossils
1. Sedimentary fossils
2.  Molds
3. Casts

2. 1. Sedimentary Fossils · Found in sedimentary rock.
· Develop from hard body parts of animals, like teeth, bone and shells or woody stems of plants.
* Hard minerals replace the tissue leaving rock like structures

3. 2. Molds
An imprint in rock the shape of an organism.

4. 3. Casts
Rocklike model of an organism which is filled with hard minerals.

5. Fossils
People started noticing these things in the late 1600’s. Robert Hooke published in 1668 his conclusion that fossils are remains of plants and animals. He was the first to study fossils with the aid of a microscope. He saw fossils and said they were too detailed to be rock so they had to be organisms that were embedded in the rock.

6. Distribution of Fossils
· Nicolaus Steno (1669)
Proposed Law of Superposition which states that successive layers of soil or rock deposited on top of one another by wind or water.
The lowest stratum (layer) in a cross section is the oldest part of earth
The top stratum is youngest
Fossils in a single stratum are approximately the same age. 

7. Law of Superposition

8. Fossils
· Relative age
* A given fossil is younger or older than another fossil.
· Absolute age
* Age in years (usually determined by C-14 dating).
All this gives a table of the history of Earth. From Precambrian (prokaryotes) to Cenozoic (current and modern humans).

9. Succession of Form
Fossil bearing strata show organisms appear, exist and then disappear. Extinct, then in turn new species arise.

10. Mass Extinctions For example, dinosaurs
· Periods where large numbers of species disappeared.
· Drastic changes in environment maybe due to volcanoes. The volcanic ash may have blocked sun and decreased temperature.

11. Biogeography
· The study of the geographical distribution of fossils and of living organisms.
· Comparison of recently formed fossils with types of living organisms in same geographic area shows new organisms arise where similar forms already lived and that they are just modified forms.
*Ex. Modern kangaroos appear only in Australia where the extinct giant kangaroo had lived.