1. A Long Time Ago
7th FOSS Earth History

2. New VOCAB: era
Please look at your ‘Personal History’ timeline. Many of you asked: ‘What is an era?’
According to your timelines, what decisions did you make when you re-read “…think about significant events in your life. Using these events, divide your timeline into three or four eras.”?
Era: A period of time in history, starting at one date and ending on another.

3. 1 of 4
The age of the Earth
Geologists & astronomers have determined that Earth, came into existence about 4.5 billion years ago (BYA).
4.5 billion = 4,500,000,000
You created a time line representing your own personal history. I also created a time line to represent the history of Earth. Instead of paper, I used mason line.

4. 2 of 4
The age of the Earth
What scale did you use for your personal time line?
Would I be able to use your same scale for a time line of Earth history?
Instead, I used a scale of:
1 cm = 1 million years.
Using my scale, how long is my time line of Earth history?
In your notebook, please show your math as you figure out an answer.

5. 3 of 4
The age of the Earth

6. 4 of 4
The age of the Earth

7. 1 of 9
Time line review

8. Time line review: Human History
2 of 9
Time line review: Human History
Scientists have discovered remains of human beings as we know them, Homo sapiens, dating back 40,000 years.
Homo erectus, or the first upright human, lived about 1.6 mya during a period we call the Stone Age.

9. Time line review: The Ice Ages
3 of 9
Time line review: The Ice Ages
Before modern human beings existed of Earth, there was a period of time called the ice ages. Great glaciers, or sheets of moving ice, covered large portions of the Earth.
Animals such as woolly mammoths and huge camels roamed the land.
Scientists think the ice ages began about 2 mya.

10. Time line review: The Ice Ages
3 of 9
Time line review: The Ice Ages
The fossil remains of a primitive human that scientists call Lucy were discovered in Africa. She lived about 3.5 mya.

11. Time line review: Dinosaurs
5 of 9
Time line review: Dinosaurs
One era that most people have heard about is the age of reptiles, or the time of the dinosaurs.
Using fossil evidence and other evidence from rocks, scientists think the last dinosaurs lived about 66 mya.
Evidence also suggests that the first dinosaurs live about 245 million years ago.

12. 6 of 9
Time line review
Geologists call the era from 245 mya to 66 mya, the Mesozoic era.
Mesozoic is derived from the Greek language and means “middle life.”
We live in the Cenozoic era, which is all of the time since the dinosaurs. Cenozoic means “recent life.”

13. Time line review: The Great Extinction
7 of 9
Time line review: The Great Extinction
Just before the dinosaurs appeared, before the Mesozoic era, there was a great extinction.
More than 90% of all species of marine life disappeared at that time. This extinction occurred at the end of what geologists call the Paleozoic era, the period of “ancient life.”
The Paleozoic era lasted from 570 mya to 245 mya.

14. Time line review: First Life on Earth
8 of 9
Time line review: First Life on Earth
All of the time before the Paleozoic era is called the Precambrian era.
It wasn’t until the end of the Precambrian era around 600 mya that complex life on Earth actually came into being, according to scientists who interpret the fossil record in the rocks.
The oldest life identified from fossils so far is a form of bacteria. It has been given an age of 3.5 billion years.

15. Time line review: Earth forms
9 of 9
Time line review: Earth forms
Scientists have determined that the age of Earth is about 4.5 billion years.
Our time line is 45 m long, and 1 cm equals 1 million years.
Looking back along the time line to where we started, to where our lifetime is located, where on the time line do we (our class) seem to know about Earth’s history?

16. Review Geological Time
Look at your four questions you answered after we were outside for the Mason Line activity.
I’d like one person per question to read their response.

17. Intro Adding-Machine-Tape Time Lines
Each pair is going to make a time line on adding-machine tape, only the tape won’t be 45 m long like the class time line.
It will be only 4.5 m long.
What scale did we use on the 45-m-long time line?
What will the scale be on the 4.5-m-long time line if we want to represent 4.5 billion years of Earth history?
You have five minutes with your partner to calculate the scale.

18. Partners are… Jano/Josh Zeb/Dalton Michael/Chase Haydn/Jessie
Brooke/Callie
Courtney/Abi
Symone/Brianna

19. Intro Geological Time Scale/Eras
1 of 3
Intro Geological Time Scale/Eras
Just as you subdivided your personal history into eras, geologists have subdivided Earth’s history into eras.
Eras are based on the kinds of living organisms that existed during four very large chunks of time.

20. Intro Geological Time Scale/Eras
2 of 3
Intro Geological Time Scale/Eras
The four eras are:
Precambrian era, the time between the beginning of Earth and the appearance of the first complex forms of life.
Paleozoic era, the age of ancient life, which ended with the Great Extinction, during which 90% of the species living in the ocean disappeared.

21. Intro Geological Time Scale/Eras
3 of 3
Intro Geological Time Scale/Eras
Mesozoic era, the middle age of life, the time of the dinosaurs.
Cenozoic era, the age of recent life, during which mammals thrived. We live in the Cenozoic era.

22. 1 of 2
New VOCAB: PERIOD
Geologists further subdivide the eras into smaller parts called periods.
Period: Eras that are further divided into smaller parts. They are based on evidence of major events that took place in Earth’s crust, such as new mountain ranges being uplifted.

23. 2 of 2
New VOCAB: PERIOD
For example, the Cretaceous period, which extended from about 144 mya to maybe 66 mya (part of the Mesozoic Era), takes its name from a particular set of chalk cliffs in southern England and northern France that were being laid down during those 80 million years.

24. White Cliffs of Dover; Seaford, Sussex, UK.
Source:

25. White Cliffs of Dover; Seaford, Sussex, UK.
Source:

26. Grand Canyon Rocks on the Time Line
Mention at least four things you did on the adding-tape time lines.
Geologists who have studied the Colorado Plateau rocks that are exposed in the Grand Canyon have methods to help them determine when the rocks were deposited.

27. Rocks over Time lab sheet
Please look at the column called “Time of Deposition”.
This column lists the period during which geologists think these rocks formed.
For example, they think that the ocean in which the Kaibab Formation was deposited existed between 260,000,000 and 255,000,000 years ago.
If the geologists are right, how long did the Kaibab Sea exist?
1 of 3

28. Rocks over Time lab sheet
Your task today is to add the Grand Canyon rocks to your time lines.
You will use the info on the Rocks over Time chart to plot the rocks on your time line.
This will provide another way of looking at the info.
The following slide demonstrates how to do this with the Kaibab Formation.
2 of 3

29. Rocks over Time lab sheet
A. Calculate how far back you need to measure from zero to the time when the Kaibab Formation was beginning to be deposited.
B. Calculate the distance you need to measure back for the time when deposition of the Kaibab Formation stopped.
C. Measure these two distances and draw lines as indicators.
D. Shade in the area between the two lines.
E. Label the shaded area “Kaibab Formation.”
Please do this for each of the rock layers listed.
3 of 3

30. Discussing the time lines
During which geological era were these rocks deposited?
How old is the oldest Grand Canyon rock you added to your time line?
What is the youngest rock exposed at the Grand Canyon?
1 of 2

31. Discussing the time lines
Please look at the very large Grand Canyon - view from the rim poster.
Where would you find the Kaibab Formation on this poster?
Are there any rocks on top of the Kaibab Formation in the Grand Canyon?
Why do you think there are no rocks exposed at the Grand Canyon that are younger than the Kaibab Formation?
2 of 2

32. Contemplating those gaps…
Some of you were concerned about the gaps between some of the rock layers as you laid them out our time line. Where are those gaps?
Please turn to pgs and 27 in your Earth History Resources books.
1 of 2

33. Contemplating those gaps…
When we look at photographs of the Grand Canyon layers, do we see those gaps?
How can you explain those gaps in time?
How much time is there between the Limestone and the Temple Butte Limestone?
What do you think could have happened in this region during that period of 150 million years?
2 of 2

34. New CONCEPT: unconformity
The only place geologists can find clues to what happened in Earth’s history is in the rocks.
If there are no rocks, there are no clues.
It’s just like a book from which someone has torn a handful of pages.
If the pages aren’t there, it’s difficult to tell what happened in the story at that point.
1 of 4

35. New CONCEPT: unconformity
Geologists call a gap in the rock record like you see here in the Grand Canyon an unconformity.
In your notebooks, based on your timeline and the last slides, write what you think unconformity means.
2 of 4

36. New CONCEPT: unconformity
I think unconformity is…
Rock layers get squished together and misplaced rocks are jammed into open spots.
Gaps between rocks of different periods of time when a new rock formed and older rock formed around it.
Rocks are formed differently by disasters and they have the key to the problems in the past. They can be solved in the future. Perhaps the rocks formed where they wanted to.
3 of 4

37. New CONCEPT: unconformity
Unconformity: An interruption in the normal sequence of deposition of sedimentary rocks or between sedimentary rocks and other kinds of rocks.
The unconformities you have discovered happened either because no rocks were ever deposited or because rocks that were deposited eroded away before the next layer was deposited.
4 of 4

38. Adding Supergroup to time lines
There is a layer of rocks below the Tapeats Sandstone, called the Grand Canyon Supergroup (a formation of limestone, shale, and sandstone).
The beginning of the deposition started about 1250 mya (1.25 bya) and deposition of the supergroup ended about 825 mya.
Please add the time segment for the deposition of the Grand Canyon Supergroup to the Rocks over Time sheet.
1 of 2

39. The Great Unconformity of the Grand Canyon
You may notice that this results in another unconformity.
The other unusual thing about the Supergroup is that this layer is not horizontal but at a slant.
Speculate on what geological processes might have caused this layer to slant.
Tapeats Sandstone started formation 545 mya and the supergroup ended 825 mya, leaving a gap of 280 million years.
This is called the GREAT UNCONFORMITY of the Grand Canyon.
2 of 2

40. Another problem
To help you develop a concept of how much time it takes for the Grand Canyon rock layers to be deposited, work out the following problem:
Redwall Limestone has an avg thickness of about 150-m but can vary from 125 to 220-m. Geologists estimate that the Redwall Limestone was deposited over a period of 35 million years.
For 150-m to be deposited in 35 million years, how much limestone would be deposited during 1000 years? 100 years? (remember, 1 m = 100 cm or 1000 mm.)