1. CO- The Geologic time scale and geologic history
CO- The Geologic time scale and geologic history. LO- describe in writing the eras of the Geologic Time scale

2. The Geologic Time Scale
Measured in millions or billions years (instead of hours and days)
Represents 4.6 billion years of Earth history
It is divided into time periods based on the rock and fossil record.

3. The Geologic Time Scale is divided into eons, eras, periods, and epochs based on one or more of the following:
major changes in earth’s surface
Major changes in earth’s climate.
major changes in the life forms on earth.

4. Dividing up Geologic Time
The Geologic Time Scale:
Is divided into Eons
Which are broken down into Eras
Which are broken down into Periods
Which are broken down into Epochs

6. Four major eras in the geologic time scale.
Precambrian Time – 88% of geologic time
Paleozoic- Ancient Life
Mesozoic- Middle Life
Cenozoic –Recent Life

7. Precambrian Eon – 88% of geologic time
From 4500 to 540 million years ago
Life on earth begins –
Single celled organisms lived
pre- “ multicellular life”
Oldest layers of rock
Bacteria and Cyanobacteria (Blue-Green algae)
Evolution of first multicellular begins at the end

8. Paleozoic Era- Ancient life
million years ago.
Evolution of multi-cellular organisms
Invertebrates fish and amphibians
Evolution of land plants land Ended with the “Permian Mass Extinction”-90% of all life went extinct.

9. Mesozoic Era -Middle life
million years ago
more complex organisms
Age of reptiles
dinosaurs
Reptiles, birds, first mammals
Ended with mass extinction – “asteroid impact”

10. Cenozoic Era – recent life
65 million years ago to present
Age of mammals
Humans take over the world

11. CO-Determining earth’s age and history.
LO-Describe in writing how we determine the age of the earth

12. How Old Is The Earth?
Scientists estimate that the earth is about billion years old.
The dating of the earth is based on evidence found in layers of rock in the earths crust and from meteorites.
The events in Earth’s geologic history has been determined through a combination of fossil evidence and absolute and relative dating techniques.

13. Relative V.S Absolute Time
Relative age - Relative means that we can determine if something is younger than or older than something else. Relative time does not tell how old something is, all we know is the sequence of events.
For example: the sandstone in this area is older than the limestone.

14. Absolute age- Absolute age means that we can more or less precisely assign a number (in years, minutes, seconds, or some other units of time) to the amount of time that has passed. Thus we can say how old something is.
For example: The sandstone is 300 million years old.

15. Relative vs. Absolute Dating
Absolute Dating is determining an exact age of something. This is done primarily with a technique known as radiometric dating.
Radiometric dating
Radioactivity discovered in 1896.
By 1905 the first time radioactive dating attempted.
By measuring the amount of a known radioactive element left in a rock, and knowing the rate of decay of that element, we can tell how old it is

16. RELATIVE DATING
The Earth’s Crust is made up of layers of rock called Strata
Relative Dating – is the science determining the relative order of rock layers and past events.
- By using a series of principles (laws) the relative age of rock layers and order geologic events can be determined.
can only determine the sequential order in which a series of events occurred, not when they occur

17. The Law of Uniformitarianism
The current geologic forces and processes are the same processes that were at work in the past.
These processes include:
-erosion and deposition
- volcanism
- plate tectonics

18. The Law of Superposition
In an undisturbed sequence of rocks that is deposited in layers:
the youngest layer is on top and the oldest on bottom
each layer is younger than the one beneath it and older than the one above it.
For example- The Grand canyon

19. The Law of Superposition

20. The Law of Superposition

23. Law of Original Horizontality
The Law of Original Horizontality:
Most sedimentary rock layers, when originally formed, were laid down horizontally.
If rock layers are not horizontal, we know that some geologic process changed them and that this process occurred after the layers were originally laid down. Processes include:
folding and tilting.

24. The Law of Original Horizontality

28. The Law of Cross-Cutting Relationships
The Law of Cross-Cutting Relationships states that a fault or body of rock is younger than any other body of rock that it cuts through.
Things that cut through rock layers are:
Faults
Igneous Intrusions

29. List these in order from oldest to youngest.