1. The geologic time scale
Earth History
The geologic time scale

2. Geologic Time Scale
The geologic time scale divides Earth’s history into sections defined by major changes on Earth.

3. Geologic Time Scale
The divisions of geologic time scale have no set length.
Some eons, eras, periods, and epochs are longer than others.

4. Geologic Time Scale Eon Era Era Period Period Period Period Epoch

5. Geologic Time Scale
The first 4 billion years of Earth’s history is called Precambrian Time
(4.6 BYA-544 MYA)

6. Precambrian Time
Notable events of
Precambrian Time:

7. Precambrian Time
Earth formed (4.6 BYA)

8. Precambrian Time
First fossilized organisms- Stromatolites (3.5 BYA)

9. Precambrian Time
Earth’s early atmosphere had very little Oxygen.

10. Precambrian Time
Early bacteria did photosynthesis, which releases Oxygen.
This went on for millions of years, filling Earth’s atmosphere with Oxygen.

11. Precambrian Time
Natural selection led to animals that used and required Oxygen to survive.

12. Precambrian Time Mass Extinction (544 MYA)
Caused by geologic and climate changes.

13. Mass Extinctions
All the major divisions of the geologic time scale are due to mass extinctions.
Mass extinction-the dying off of many species at one time.

14. Mass Extinctions 99% of all species that ever lived are extinct!
Mass extinctions can be caused by: climate change, volcanic eruptions, asteroid impacts, etc.

15. Paleozoic Era ( MYA)
First animals with hard parts (shells) MYA

16. Paleozoic Era
Cambrian explosion- rapid expansion and evolution of animals with shells.

17. Paleozoic Era
First fish (500 MYA)

18. Paleozoic Era
First land plants (470 MYA)

19. Paleozoic Era
First insects (400 MYA)

20. Paleozoic Era
First trees (385 MYA)

21. Paleozoic Era
First amphibians (370 MYA)

22. Paleozoic Era
First amniotes (egg laying animals): 360 MYA

23. Paleozoic Era
The first amniotes would become the ancestors of all dinosaurs, reptiles, and modern mammals (including us!)

24. Paleozoic Era
The Carboniferous period had huge insects like 10 cm cockroaches and 74 cm dragonflies!

25. Paleozoic Era
Pangaea formed (270 MYA)

26. Paleozoic Era Permian-Triassic Mass Extinction (245 MYA)
90% of everything on Earth was wiped out.

27. Paleozoic Era
The Permian- Triassic extinction is the largest mass extinction in Earth’s history- called “the Great Dying.”

28. Mesozoic Era ( MYA)
First dinosaurs (230 MYA) .

29. Mesozoic Era
First mammals (220 MYA) .

30. Mesozoic Era
Pangaea breaks apart (200 MYA)

31. Mesozoic Era Triassic-Jurassic Extinction (200 MYA)
Likely due to climate change, rising sea levels, and an increase in atmospheric CO2

32. Mesozoic Era
After the Triassic- Jurassic extinction, dinosaurs dominated the Mesozoic.

33. Dinosaurs
Stegosaurus ( MYA)

34. Dinosaurs
Tyrannosaurus Rex ( MYA)

35. Dinosaurs
There was more time between the Stegosaurus and the T- Rex than between the T- Rex and you!

36. Mesozoic Era
Modern day birds are the living descendants of dinosaurs.

37. Mesozoic Era
Archaeopteryx is an important fossil from the Jurassic period linking birds and dinosaurs.
It is a dinosaur-like skeleton with fossilized feathers.

38. Mesozoic Era
First Birds (150 MYA)

39. Mesozoic Era
First flowering plants (140 MYA)

40. Mesozoic Era
Near the end of the Mesozoic Era, mammals increased in numbers as dinosaurs began to go extinct.

41. Mesozoic Era K-T Mass Extinction (66 MYA)
An asteroid impact was a major reason for this extinction.
Volcanic eruptions may have also played a role.

42. Mesozoic Era
85% of all living things were wiped out, including the remaining dinosaurs.
Luckily for us, many mammals survived.

43. Cenozoic Era (66 MYA-Present)
The Cenozoic Era is known as “the age of mammals.”

44. Cenozoic Era
The descendants of the organisms that survived the Cretaceous extinction (66 MYA) are the organisms that we know today.

45. Cenozoic Era
Some mammals evolved BACK into the ocean during the Cenozoic to become modern marine mammals like whales and dolphins.

46. Cenozoic Era
First Horses (60 MYA)

47. Cenozoic Era First Primates (55 MYA)
Primate- forward facing eyes, hands and feet, and opposable thumbs

48. Cenozoic Era
Early Hominins (primitive humans) 3.5 MYA

49. Cenozoic Era
Most recent ice age began (2 MYA)

50. Cenozoic Era
Homo erectus (upright man) 1.6 MYA

51. Cenozoic Era
Homo erectus went extinct 143,000 years ago

52. Cenozoic Era
Homo sapiens (Us!) ~200,000 years ago

53. Cenozoic Era
We are the first and only species of hominin to not share the planet with other hominin species.