1. Geologic Time Scale

2. Earth’s History Continued…
Now that we have all of these pieces of evidence, we are able to reconstruct a timeline of Earth’s History…we call this timeline the Geologic Time Scale.

3. What do we call these major events or changes?
Geologic Time Scale
Geologic Time Scale – a timeline of Earth’s History divided by major events or changes on Earth
What do we call these major events or changes?

4. Catastrophic Events
Catastrophic Events – events that cause major destruction or change life completely
Examples:
Mass extinctions
Ice Ages
Meteor strikes
Major volcanic eruptions

5. EONS – largest division of time 4 Eons of Time:
1. Hadean
2. Archean
3. Proterozoic
4. Phanerozoic
The first 3 eons make up Precambrian Time which is 90% of Earth’s History! It lasted nearly 4 billion years of Earth’s 4.6 billion year history!

6. PRECAMBRIAN TIME MAIN EVENTS:
After Earth & its moon were formed, there was…
Major volcanic activity leading to the formation of Earth’s Crust!
Oxygen levels in the atmosphere rise!
Single-celled micro-organisms; simple multi- celled organisms, like sponges & jellyfish, in the ocean towards the end.
NO animals or plants on land!

7. Phanerozoic Eon – 544 million years ago – present day
Explosion of Life!
Contains 3 Eras:
Paleozoic Era – “Age of Amphibians”
Mesozoic Era – “Age of Dinosaurs”
Cenozoic Era – “Age of Mammals”

8. Paleozoic Era = “Ancient”
544 mya – 248 mya
More diverse marine life such as fish and amphibians developed
Life begins moving onto land towards the end of this era
Reptiles, insects, and simple land plants like ferns developed
Pangaea exists about 280 million years ago
Ends with a Mass Extinction possibly from a meteor strike (???) – kills 90% of all ocean species and 70% of land dwellers!

9. Mesozoic Era = “Middle”
248 mya – 65 mya
Pangaea begins to break apart about 200 million years ago!
Dinosaurs rule the land!
Small early mammals, birds, and more complex flowering plants and flying insects are seen
Ends with another Mass Extinction due to meteor strike off the coast of Mexico
Dust cloud blocked sunlight, killed plant life and affected the food chain

10. Cenozoic Era =“Recent”
65 mya – Present
First primates appear
Primitive whales enter the ocean
Larger land mammals like horses, pigs (have hooves) cats, dogs, bears
Animals developed migration techniques and coevolution patterns
Quaternary Period = the past 2 million yrs
Last Ice Age ends
1st modern humans leading to Homo Sapiens and modern civilizations

11. Geologic Time Scale Summary
The Geologic Time Scale is divided by catastrophic events; not equal time segments!
In general, life goes from simple to more complex!
Most life occurs towards the end of the Geologic Time Scale!

12. The Clock of Eras
The last comparison put Earth’s Geologic Time Scale into 1 year – but what if we put it into 1 day?
om/watch?v=H2_6cq a2cP4