1. Fossils & History of the Earth.

2. Fossils and Superposition
What is a fossil?
The trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock
What is a superposition?
Younger rocks lie above older rocks if the layers have not been disturbed

3. How a Fossil Forms - Fossils
Most fossils form when living things die and are buried by sediment. The sediment slowly hardens into rock and preserves the shapes of the organisms.

4. Fossil Types
1) Mold = hollow impression of a living thing in rock after it
2) Cast = solid mineral deposit that filled a mold, leaving a copy of the living thing

5. Fossil Types continued
Trace fossils –

6. Fossil Types continued.
3) Body fossils – actual parts of an organism bones, shells, leaf imprints

7. impressions of passage of living things
Fossil Types continued
4) Burrows or borings –
Spaces dug out by living things & preserved as is or filled in
5) Tracks –
impressions of passage of living things

8. Fossil Types continued
6) Imprint –
Thin objects such as a leaf that falls onto sediment & leaves an imprint then the sediment hardens into rock

9. parts of an organism producing a copy of them
Fossil Types continued
7) Petrified Fossils
Minerals penetrate
& replace the hard
parts of an organism producing a copy of them
8) Amber & Ice
An entire organism was quickly trapped in ice or tree sap that hardens into amber

10. Sedimentary Rock Where are fossils found?
What type of rock formation is this? Sedimentary, Metamorphic, or Igneous? Sedimentary, you can see the layers. 10

11. What conditions promote fossilization?
1) Hard body parts such as skeletal bones or exoskeletons
2) Rapid burial and/or lack of Oxygen

12. Sporadoceras Nautilus
Sporadoceras, which lived during the Devonian period 350,000,000 years ago, are extinct relatives of the chambered nautilus.  The shells of these creatures accumulated on the sea floor and were buried in sediment.  Over the ages they hardened to stone.  Today they are quarried from what is now the Sahara Desert in Morocco.
Nautilus 12

13. Orthoceras
Orthoceras were marine, or sea animals similar to modern squid.  They had a shell shaped like a cone.  Orthoceras were active swimmers in warm shallow seas and swam by squirting water out of the body cavity.  They ate small animals and some grew to be 6 feet long.  In the fossilized remains of the shell, you can often see different chambers where the animal lived
Squid 13

14. Trilobites
Scientists think that trilobites were the first multiple-celled animal to exist on earth.  These extinct sea animals had exoskeletons, or outer armor, that was divided into 3 parts.  Some crawled on the sea bed, some floated and some swam.  The lived all over the world.  Crabs and lobsters are modern relatives.
Lobster 14

15. Fossil Fish
Fish are the oldest and most primitive type of vertebrate.  The first fish were small, the size of a minnow.  They had heavy, bony plates for skin.  They lived on the ocean floor and are through slits on both sides of their throats.  Later, fish began to develop gills, scales and fins and learned to live in fresh water, too.  Some even developed lungs.  Over half the species of vertebrates, both living and extinct, are fish 15

16. Dinosaur Bones
The word dinosaur means "terrible lizard".  Dinosaurs  were reptiles that lived throughout the world and dominated the land for over 140 million years.  Some were as small as a rooster in size.  Other grew to be the largest land animals ever to live and weighed up to 80 tons.  Many dinosaurs ate plants.  Others were meat eaters.  They began to die out when the Earth's climate became colder and plant life changed. 16

17. - Fossils
Changes Over Time
The fossils record provides evidence about the history of life and past environments on Earth. The fossil record also shows that different groups of organisms have changed over time.

18. Changes Over Time - Fossils
From fossils, scientists have reconstructed the paleomastodon. This animal had a short trunk and short tusks on both the upper and lower jaws. The paleomastodon is an ancestor of the modern elephant.

19. The Position of Rock Layers
- The Relative Age of Rocks
The Position of Rock Layers
According to the law of superposition, in horizontal sedimentary rock layers, the oldest layer is at the bottom. Each higher layer is younger than the layers below it.

20. Determining Relative Age
- The Relative Age of Rocks
Determining Relative Age
To determine relative age, geologists also study extrusions and intrusions of igneous rock, faults, and gaps in the geologic record.

21. Determining Relative Age
- The Relative Age of Rocks
Determining Relative Age
An unconformity occurs where erosion wears away layers of sedimentary rock. Other rock layers then form on top.

22. Using Fossils to Date Rocks
- The Relative Age of Rocks
Using Fossils to Date Rocks
Index fossils are useful because they tell the relative ages of the rock layers in which they occur.

23. Index Fossil Activity - The Relative Age of Rocks
Web Site: PHSchool.com
Code: cfp-2042

24. Asking Questions - The Relative Age of Rocks Question Answer
What does the position of rock layer reveal?
The oldest layers—and the oldest fossils—are at the bottom.
How do geologists determine the relative age of a rock?
They examine the position of rock layer, extrusions and intrusions of igneous rock, faults, and gaps in the geologic record.
How are fossils used to date rocks?
The age of an index fossil tells the age of the rock layer in which it occurs.

25. Determining Absolute Ages
- Radioactive Dating
Determining Absolute Ages
Radioactive Decay = During radioactive decay, the atoms of one element break down to form atoms of another element.

26. Radioactive Decay - Radioactive Dating
The half-life of a radioactive element is the amount of time it takes for half of the radioactive atoms to decay.

27. Determining Absolute Ages
- Radioactive Dating
Determining Absolute Ages
Geologists use radioactive dating to determine the absolute ages of rocks.

28. Determining Absolute Ages
- Radioactive Dating
Determining Absolute Ages
The age of a sedimentary rock layer can be determined relative to the absolute age of an igneous intrusion or extrusion near the sedimentary rock.

29. The Geologic Time Scale
Because the time span of Earth’s past is so great, geologists use the geologic time scale to show Earth’s history.

30. Earth’s Surface Forms - Early Earth
During the first several hundred million years of Precambrian Time, an atmosphere, oceans, and continents began to form.

31. Life Develops - Early Earth
Scientists have found fossils of single-celled organisms in rocks that formed about 3.5 billion years ago. These earliest life forms were probably similar to present-day bacteria.

32. Mass Extinctions - Eras of Earth’s History
The graph shows how the number of families of animals in Earth’s oceans has changed.

33. Mass Extinctions - Eras of Earth’s History Interpreting Data:
How long ago did the most recent mass extinction occur?
Slightly more than 50 million years ago

34. Mass Extinctions - Eras of Earth’s History Interpreting Data:
Which mass extinction produced the greatest drop in the number of families of ocean animals?
The one that occurred about 230 million years ago

35. Mass Extinctions - Eras of Earth’s History Relating Cause and Effect:
In general, how did the number of families change between mass extinctions?
The number of families of ocean animals immediately dropped but then increased.

36. - Eras of Earth’s History
Geologic History

37. Continental Drift Activity
- Eras of Earth’s History
Continental Drift Activity
Web Site: Phschool.com
Code: cfp-1015