1. The Fossil Record
Evidence of Change

2. Fossils What are fossils? What is the fossil record? How do they form?
Types of fossils
What do they tell us?
Determining their age

3. The Data is in the Strata
Modern day science accepts the idea that the layers of the Earth show the past.
Different layers have different kinds of fossils.
That means life on Earth has changed (evolved).
The pattern of fossils changing can be found around the world.
The same fossils in different places mean the rocks are the same age.

4. What are fossils? Any preserved evidence of an organism
Evidence can be the preserved remains of plants or animals that lived a long time ago
Or any other preserved indications of their existence
Imprints
Molds & casts

5. How fossils form
Most fossils form when organisms that die become buried in sediments
Some remains that become buried in sediments actually change to rock
Minerals dissolved in the water soak into the buried remains changing them into rock. Fossils that form this way are called petrified or replacement fossils
Sometimes shells or other hard parts buried by sediments gradually dissolve and form an empty space
The hollow space in the sediment that is in the shape of the organism is called a mold
When the space becomes filled in with hardened minerals, a cast, or copy of the shape of the organism is formed

6. How fossils form
Sometimes organisms are preserved in substances other than sediments
Organisms such as the mammoth have been perfectly preserved in ice
Insects like the mosquito
have been preserved in the
sap of trees called amber

7. Types of fossils Trace Molds and Casts Replacement
Petrified or Permineralized
Amber
Freezing or Mummification

8. Trace Fossils
Trace fossils are indications that an organism existed, not the actual organism. They include footprints, nests, tooth marks, worm burrows, root traces, etc.

9. Molds and Casts Molds Casts
A mold forms when something is pressed into soft mud and removed by decomposition or pulled out, leaving an impression of the object.
Casts
A cast is a 3-D representation of an object from the past. It is created when a mold fills up with sediment that hardens.
Molds and casts are actually two common types of trace fossils. A mold forms when something is pressed into soft mud and removed by decomposition or pulled out, leaving an impression of the object. A cast is a 3-D example of an object of the past created when a mold fills up with sediment like mud, sand or volcanic ash.

10. Replacement and Petrification (Altered Preservation)
The organism is preserved but its original skeletal material or pores are filled with or replaced with mineral crystals
Ex: petrified wood is no longer made of wood, it has actually turned stone.

11. Assignment: Read pages 189 - 190 in your text, complete guided reading and study handout.
(Due: Weds 3/4/2015) 11

12. The Fossilization Process 12

13. What do fossils tell us?
Fossils can act like pieces in a jigsaw puzzle, helping scientists piece together information about Earth’s past.
They provide a history book of past life forms (with many missing pages)
Lets us know of extinct life forms that once lived on earth (99% of all life forms on earth are now extinct)
Shows us that there have been transitional species and evolution of species
The millions of fossils that scientists have collected are called the fossil record

14. Dating Fossils Relative Dating The Law of Superposition
Determine the relative age of rocks and fossils by comparing them with other layers
The Law of Superposition
Relative dating is based on the law of superposition
A sedimentary rock layer is older than the layers above it and younger than the layers below it if the layers are not disturbed
It is not a coincidence that older fossils of more primitive life forms are found at deeper and deeper layers

15. Index Fossils
Species go extinct and others appear and sometimes they overlap for a brief time.
Index fossils = fossils or combinations that indicate a specific time.

16. Match the layers, 0 is oldest, 7 is youngest.
Same fossils means the same layer.
Some layers or evidence may be missing.

17. Use the fossils to put the layers in order from youngest to oldest.
B H I JE K CL FD G

18. Radioactive Dateing
Relative Dating tells us what is older but not the actual ages.
To find the actual age of rocks we use radioactive elements.

19. Radioactive Elements & Decay
Radioactive elements are made of atoms whose nucleus is unstable
Decay = when the nucleus of a a radioactive atom releases energy and a particle (proton, neutron or both) and becomes a new element

20. Half-Life
The amount of time it takes for one half of a radioactive substance to decay into a nonradioactive substance.

21. Half-life Graph
Number of half-lives x half-life years = age of the rock

22. After death the C-14 in an organisms body decays
After death the C-14 in an organisms body decays. After one half-life (5730 years), the amount of atoms gets cut in half. 22

23. One half-life (5730 years later) only one half of the C-14 is left23

24. Two half-lives (2 x 5730 = 11460 years later) only ¼ of the C -14 is left24

25. Three half-lives (3 x 5730 = 17,190 years later) how much C-14 is left?
1/8 of the C-14 is left 25

26. Four half-lives (4 x 5730 = 22,920 years later)
1/16 of the C-14 is left 26

27. Carbon 14 dating is only useful to date objects 60,000 years or younger because too little is left to measure accurately past this point 27

28. Elements Used for ½ Life dating
Carbon-14 is in all living things but can only be used for things about 60,000 years old
To age the Earth and most Fossils we use elements with longer half lives.
Radioactive Parent
Stable Daughter
Half life
Potassium 40
Argon 40
1.25 billion yrs
Rubidium 87
Strontium 87
48.8 billion yrs
Thorium 232
Lead 208
14 billion years
Uranium 235
Lead 207
704 million years
Uranium 238
Lead 206
4.47 billion years

29. Assignment Read pages 191 to 195 in your text
Complete the Guided Reading handout.
Due: Friday 3/6/2015