1. Have a seat quickly and quietly
Today we will be continuing our Guided Notes about the History of Earth

2. Earth's History: Geological Time, Rocks, Fossils
15 Billion Years in 3 Minutes

3. Geological Time Scale
A timeline that organizes the events in Earth’s history.
Earth is about 4.6 billion years old.
More complex organisms such as land plants and fish evolved only within the last 500 million years.

4. Humans Humans evolved only about 110, 000 years ago
If Earth’s history were shortened into a single day, humans would not evolve until the last few seconds.

5. Calendar of Earth
The geological time scale is like a calendar extending from earth’s formation to the present.
The scale is divided into eons, eras, periods, and epochs.

6. Giving Time a Name The largest sections are called “eons”
“Eons” are divided into “eras” (the 2nd largest section)
“Eras” are divided into “periods”
Then “periods” are divided into “epochs”
Usually the oldest sections are shown on the bottom and the most recent sections are shown on the top

7. How is Time Divided?
Major changes in Earth’s history mark the boundaries between the sections
Most sections have been divided because a major organism developed or went extinct.

8. Extinction Extinction = the death of every member of a species
It can happen because of competition between the species, so some organisms ran out of food or space
It can happen because the environment changed, and some organisms could not survive in the new environment.

9. Other Causes of Extinction
Increase in temperature
Increase or decrease in rainfall
Volcanic eruption
Flooding or drought
Shifting land or sea
A change in food supply
A new predator or disease

10. Mass Extinction
Mass extinction = the extinction of many species at the same time
Can you think of an example of a mass extinction?
It can be caused by gradual changes in climate or ocean currents (Uniformitarianism)
Or by catastrophic events, like an asteroid hitting the earth and blocking out the sun (Catastrophism)

11. BrainPop- Extinction
ment/extinction/

12. Precambrian Time

13. Precambrian Time
Time from the formation of the Earth (4.6 billion years ago) to 542 million years ago
The Earth was very different then
At first, there was no oxygen or living things
Then the first organisms appeared in the oceans billion years ago
They were called Prokaryotes

14. Prokaryotes Only one cell and no nucleus
One type, Cyanobacteria, were the first organisms on Earth
Through photosynthesis, they released oxygen into the air
As oxygen began to build up, the ozone was formed
The ozone protects the Earth against the sun’s harmful rays (deadly to land organisms)
Now organisms could live on land too!

15. Eukaryotes
After another 1 billion years, more complex organisms developed
They were called Eukaryotes
Many cells with a nucleus
Evolved into organisms on Earth today

16. Paleozoic Era

17. Paleozoic Era
Began 542 million years ago and ended 251 million years ago
Divided into 6 periods
Many new life forms appeared during the 1st period, the Cambrian Period ; called the “Cambrian Explosion”
For the first time on Earth, organisms had hard parts (shells, exoskeletons)
Some organisms that were alive during this period still exist today (ferns and salamanders) but they were giants!

18. Permian Extinction
The largest mass extinction happened 251 million years ago
Marked the end of the Paleozoic Era and the start of the Mesozoic Era
Scientists are not sure what caused this mass extinction (maybe climate change & volcanoes)
90% of ocean life and 78% of land life died
Reptiles and amphibians survived!

19. Mesozoic Era

20. Mesozoic Era Began 251 million years ago
Surviving reptiles and amphibians evolved into many other species (like dinosaurs) = “Age of Reptiles”

21. Cretaceous-Tertiary Extinction
Another mass extinction happened 65 million years ago
Marked the end of the Mesozoic Era and the beginning of the Cenozoic Era
All of the dinosaurs and half of the other animals & plants went extinct
Scientists think an asteroid hit Earth, the dust clouds blocked out the sun, plants died, then herbivores, then carnivores.

22. Cenozoic Era

23. Cenozoic Era Began 65 million years ago and continues today
Scientists know the most about this Era because the fossils are in the top rock layers and are easier to find
Land & climate has changed a lot
What big change will happen that will end this era & start the next?

24. Geological Time Brain pop
gictime/

25. Determining the Age of Rocks
Scientists use rocks and fossils to try to date events, or determine when in history events took place on earth.
Scientists use 3 techniques of dating:
Absolute age
Radioactive dating
Relative age

26. Absolute Age
Tells the actual age of rock or fossil or how long ago an event occurred

27. Radioactive Dating
Is means of measuring the age of a material by comparing the amount of radioactive form of an element in a rock or fossil with the amount of its decay product.

28. Relative Age
When absolute age is not possible, scientists use relative age.
Relative age describes the age of an object or event in comparison to another object or event.
It determines which events occurred earlier or later then others without giving a definite date.

29. Carbon Dating
Another useful way to determine the age of a fossil or the rock it is found in is Carbon Dating
All living things contain carbon– we can measure the amount of carbon left in the fossil to determine how long ago the organism died
Cannot be used to date rocks, only once-living organisms
Can also be called “radiocarbon dating”
BrainPop- Carbon Dating

30. Law of Superposition
States that in undisturbed sedimentary rock layers, older layers of rock lie beneath younger rock layers
Older sediments must be laid down first before the younger ones pile on top.

31. Unconformity
Plate movements can disturb rock layers by folding or turning them.
Sometimes a layer can be missing one area of rock bed.
The missing layer is called an unconformity.
Makes it more difficult to understand how earth changed at a specific time.

32. Fossils Provides Clues to Earths Past
Fossils can be used to determine the geological history, or age, of the rock that contains them
Younger fossils may be found where the original boundary was an ocean/continent
Older fossils are found in where plates collided, formed mountains, and are now eroding.

33. Index Fossil fossil must be widely distributed
represent a type of organism that existed only briefly.
useful because they tell the relative ages of the rock layers in which they occur.