1. Question of the Day “The Present is the Key to the Past.”
Section 1 Geologic History
Question of the Day
“The Present is the Key to the Past.”
This phrase was the basis of the uniformitarianist theory developed by geologist James Hutton in the late 1700s.
Write a few sentences about how studying the present could reveal the story of Earth’s history. Draw a sketch to illustrate geologic processes that occurred millions of years ago that you can still see today.

2. Objectives We will compare uniformitarianism with catastrophism.
Section 1 Geologic History
Objectives
We will compare uniformitarianism with catastrophism.
We will talk about how the science of geology has changed over the past 200 years.
We will talk about the differences between relative dating with absolute dating.

3. Uniformitarianism verses Catastrophism
Section 1 Geologic History
Uniformitarianism verses Catastrophism
Uniformitarianism is the thinking that all landforms formed over long periods of time.
Catastrophism is the thinking that all landforms formed suddenly in single big events.

4. Section 1 Geologic History

5. Section 1 Geologic History
At first most people also believed that Earth was only a few thousand years old.
Earth had to be much older, because gradual geologic processes would take much longer than a few thousand years.

6. Modern Geology—A Happy Medium
Section 1 Geologic History
Modern Geology—A Happy Medium
It is now believed that catastrophes sometimes play an important role in shaping Earth’s history.
Neither theory completely accounts for all geologic change.
Most change is slow and uniformed, however, some events happen suddenly such as asteroids and earthquakes.

7. Modern Geology—A Happy Medium
Section 1 Geologic History
Modern Geology—A Happy Medium
Some scientists think an asteroid strike 65 million years ago caused the dinosaurs to become extinct.

8. Section 1 Geologic History
Relative Dating
Two methods are used to date fossils found in sedimentary rocks.
One of those methods is known as relative dating.
Relative dating examines a fossil’s position within rock layers to estimate its age.

9. Section 1 Geologic History
Relative Dating
The bottom layers of rock are usually the oldest, and the top layers are usually the youngest.
What layer a fossil is found in can determine its age.
For example, fossils in the bottom layers are usually older than fossils in the top layers.

10. Section 1 Geologic History
Relative Dating
Information on rock layers is combined from all over to form the Geologic Column, where the oldest rocks and fossils are at the bottom.

11. Section 1 Geologic History

12. Section 1 Geologic History
Absolute Dating
Scientists can use absolute dating to more precisely determine the age of a fossil or rock.
In absolute dating, scientists examine atoms to measure the age of fossils or rocks in years.
Atoms are the particles that make up all matter.

13. Absolute Dating Some atoms are unstable, and will decay over time.
Section 1 Geologic History
Absolute Dating
Some atoms are unstable, and will decay over time.
Each kind of unstable atom decays at its own rate.

14. Section 1 Geologic History
Absolute Dating
Half-life is the time is takes for half of the unstable atoms to decay.
Scientists can examine a sample of rock or fossil, and look how much of the unstable atoms are left.
Since they know the half-life, they can determine the approximate age of the sample.

15. Section 1 Geologic History

16. Section 1 Geologic History
Absolute Dating
Uranium-238 has a half-life of 4.5 billion years. Scientists can use uranium-238 to date rocks or fossils that are millions of years old.
Carbon-14 has a half-life of only 5,780 years.
Scientists use carbon-14 to date fossils and other objects that are less than 50,000 years old, such as human artifacts.

17. Radiometric Dating Section 1 Geologic History
Watch this video clip on Carbon Dating.

18. Paleontology—The Study of Past Life
Section 1 Geologic History
Paleontology—The Study of Past Life
Paleontology is the science involved with the study of past life.
Scientists collect data by studying fossils, the remains of organisms preserved by geological processes such as mud slides, volcanic ash, and natural sedimentation.
We then can recreate past environments.

19. Section 2 Looking at Fossils
Question of the Day
Describe the fossil record of your own life that might be found 65 million years from now. What items, or artifacts, might be likely to survive? What kinds of things would decay and disappear? Do you think your fossil record would produce an accurate picture of your life? What might be missing?
Write your description on your paper.

20. Section 2 Looking at Fossils
Objectives
Describe seven ways in which different types of fossils form.
List three types of fossils that are not part of organisms.
Explain how fossils can be used to determine the history of changes in environments and organisms.
Explain how we use the geologic time scale with the geologic column to find the age of fossils.

21. Section 2 Looking at Fossils
Fossilized Organisms
Fossil- Evidence of one living things preserved in sedimentary rock.
Fossils form when an organism dies and is quickly covered in sediment.
When the sediment becomes rock, hard parts of the organism are preserved.

22. Fossilized Organisms, continued
Section 2 Looking at Fossils
Fossilized Organisms, continued
Insects and some animals can become stuck in sap and be preserved.
Sap hardens and preserves hard and soft tissue.
Some of the best insect fossils, as well as frogs and lizards, have been found in amber.

23. Fossilized Organisms, continued
Section 2 Looking at Fossils
Fossilized Organisms, continued
Organisms can also be preserved by petrifaction.
Petrifaction is a process in which minerals replace the organism’s soft tissues.

24. Fossilized Organisms, continued
Section 2 Looking at Fossils
Fossilized Organisms, continued
In some places, asphalt, or tar, wells up and forms thick, sticky pools at Earth’s surface.
These asphalt pools can trap and preserve many organisms.
The La Brea Tar Pits in Los Angeles, California have preserved organisms for at least 38,000 years.

25. Fossilized Organisms, continued
Section 2 Looking at Fossils
Fossilized Organisms, continued
Organisms can also freeze and become preserved.
In 1999, scientists removed a 20,000-year-old woolly mammoth that was frozen in the Siberian tundra.
These mammoths became extinct about 10,000 years ago.
Because cold temperatures slow down decay, the mammoth was almost perfectly preserved.

26. Section 2 Looking at Fossils
Other Types of Fossils
Molds and casts are two more examples of fossils.
A cavity in rock where a plant or animal was buried is called a mold.
A cast is an object that is created when sediment fills a mold and becomes rock.

27. Other Types of Fossils, continued
Section 2 Looking at Fossils
Other Types of Fossils, continued
Trace fossils are any naturally preserved evidence of animal activity.
Tracks, or footprints, are an example of a trace fossil.
Tracks can reveal size and speed of an animal, and whether it traveled in groups.

28. Other Types of Fossils, continued
Section 2 Looking at Fossils
Other Types of Fossils, continued
Burrows are another trace fossil.
Burrows are shelters made by animals that bury themselves in sediment, such as clams.
Another type of trace fossil is coprolite, or preserved animal dung.

29. Using Fossils to Interpret the Past
Section 2 Looking at Fossils
Using Fossils to Interpret the Past
The Information in the Fossil Record The fossil record gives only a rough sketch of the history of life on Earth.
Most organisms never become fossils.
Many fossils have yet to be discovered.
The fossil record is full of gaps.

30. Using Fossils to Interpret the Past, continued
Section 2 Looking at Fossils
Using Fossils to Interpret the Past, continued
Fossils can show a history of environmental change.
For example, the presence of marine fossils on mountaintops in Canada means that these mountains formed at the bottom of the ocean.
Marine fossils can also help scientists reconstruct ancient coastlines and detect the presence of ancient seas.

31. Using Fossils to Interpret the Past, continued
Section 2 Looking at Fossils
Using Fossils to Interpret the Past, continued
Scientists can use fossils of plants and land animals to reconstruct past climates.
By examining fossils, scientists can tell whether the climate of an area was cooler or wetter than that climate is now.

32. Using Fossils to Interpret the Past, continued
Section 2 Looking at Fossils
Using Fossils to Interpret the Past, continued
History of Changing Organisms Scientists study the relationships between fossils to interpret how life has changed over time.
Since the fossil record is incomplete, paleontologists look for similarities between fossils over time to try to track change.

33. Using Fossils to Date Rocks
Section 2 Looking at Fossils
Using Fossils to Date Rocks
Scientists have found that particular types of fossils appear only in certain layers of rock.
By dating rock layers above and below these fossils, scientists can determine the time span in which the organism lived.
If the organism lived for a relatively short period of time, its fossils would show up in limited layers.

34. Geologic Time Earth is about 4.6 billion years old.
Section 3 Time Marches On
Geologic Time
Earth is about 4.6 billion years old.
Paleontologists find a record of Earth’s history in rock formations and fossils around the world.

35. Geologic Time, continued
Section 3 Time Marches On
Geologic Time, continued
The Fossil Record and Geologic Time Sedimentary rocks in the Green River formation can be found in parts of Wyoming, Utah, and Colorado.
These rocks are thousands of meters thick, and were once part of a system of ancient lakes that existed for millions of years.
Fossils of plants and animals are common in these rocks, and very well preserved.

36. Section 3 Time Marches On

37. The Geologic Time Scale
Section 3 Time Marches On
The Geologic Time Scale
The geologic column represents the billions of years that have passed since the first rocks formed on Earth.
Geologists study a total of 4.6 billion years of Earth’s history!
To make their job easier, geologists have created the geologic time scale, a scale that divides Earth’s history into distinct intervals of time.

38. Section 3 Time Marches On