1. The Fossil Record

2. Evidence of Evolution
1. Much of the evidence that is used to support the idea that organisms have changed over time is the fossil record.

3. fossils
2. A fossil is the preserved remains of an ancient organism.
It could be a part of the organism (a bone or tooth) or an imprint, such as a footprint.

6. sedimentary rock
3. Most fossils form in sedimentary rock. Over time, layers of particles build up. The weight of the layers causes the lower layers to turn into rock. If conditions are right, the remains of organisms are preserved within the rock. Many years later, weathering and erosion leave fossils exposed or near the surface.

7. sedimentary rock

8. Relative vs. Absolute Dating

9. 4. One method of determining a fossil’s age compares fossils and rock layers.
If the rock is unchanged, layers at the bottom were formed before the layers at the top.
Therefore fossils in lower layers are older than fossils in higher layers.

10. Relative Dating
5. This comparison of the ages of different fossils based on the rock layer in which it was found is called relative dating. It is useful, but it does not tell the exact age of a fossil.

11. Relative Dating
6. Performed by estimating fossil age compared with that of other fossils.

12. Relative Dating The deeper it is, the older it is.
Drawback – provides no information about age in years

13. Absolute Dating 7. Can determine the absolute age in years
It is performed by radioactive dating – based on the amount of remaining radioactive isotopes.
mya=million
years ago

14. Absolute Dating
Drawback - part of the fossil is destroyed during the test
mya=million
years ago

15. 8. Paleontologists work to group the fossils of similar organisms together. They also arrange fossils in the order in which they lived.

16. Evidence of Evolution
9. The most complete fossil record we have is of the horse.

17. 10. The fossil record is an ordered arrangement of fossils
10. The fossil record is an ordered arrangement of fossils. It shows that most of the species that ever existed on Earth are now extinct.

19. 11. Huge gaps in the record leave the explanation open to interpretation. Some scientists believe that the explanation for the gaps are from periods during which fossils were unable to form.
12. Other scientists believe the gaps show that the explanation of evolution is incorrect.

21. Evidence of Evolution
Fossils show the history of life on Earth and how different groups of organisms have changed over time.

22. Evidence of Evolution
The most complete fossil record we have is of the horse.

23. Relative Dating
Performed by estimating fossil age compared with that of other fossils
The deeper it is, the older it is.
Drawbacks – provides no information about age in years

24. Absolute Dating Can determine the absolute age in years
Is performed by radioactive dating – based on the amount of remaining radioactive isotopes
Drawbacks - part of the fossil is destroyed during the test

25. sedimentary rock
This type of rock forms through sediment being deposited and later solidifying.
It is often deposited in layers, and frequently contain fossils. (examples: limestone and shale)

26. fossils
This is the preserved remains of an ancient organism.
It could be a part of the organism (a bone or tooth) or an imprint, such as a footprint.

27. fossil record
The fossil record is an ordered arrangement of fossils.

28. Relative Dating
Performed by estimating fossil age compared with that of other fossils

29. Absolute Dating Can determine the absolute age in years
Is performed by radioactive dating – based on the amount of remaining radioactive isotopes
mya=million
years ago

30. fossil record
The fossil record is an ordered arrangement of fossils.