1. 8-2 Notes – Early Earth History
Chapter 8, Lesson 2

3. Life on Earth Changes
Paleontologists discovered that the system used to classify modern organisms could be used to classify fossils.

4. Life on Earth Changes
Fossils from rock layers that are touching are more similar than fossils from widely separated layers.

5. Life on Earth Changes
The more recent a fossil was formed, the more it resembles a living organism.

6. Precambrian Time
Precambrian time is 88% of Earth’s history, and is split into 3 eons: Hadean, Archean, Proterozoic.
88%

7. Precambrian Time
Precambrian rocks are difficult to study because they are rare, and have undergone metamorphism or been destroyed.

8. Precambrian Time: Archean Eon
Archean Eon sediments contain large amounts of the minerals pyrite and uraninite.

9. Precambrian Time: Archean Eon
Today’s atmosphere contains oxygen that quickly destroys these minerals through oxidation.

10. Precambrian Time: Archean Eon
So, we can conclude that Earth’s early atmosphere had very little oxygen.

11. Precambrian Time: Archean Eon
The absence of oxygen suggests there was no ozone layer during Precambrian time.

12. Precambrian Time: Archean Eon
Without ozone, ultraviolet rays from the sun cause death or mutations in cells.

13. Precambrian Time: Archean Eon
Changes in one gene in an organism could result in new life forms many generations later.

14. Precambrian Time: Archean Eon through Proterozoic Eon
Cyanobacteria are one of the earliest organisms, and they undergo photosynthesis.

15. Precambrian Time: Archean Eon through Proterozoic Eon
Stromatolites are mounds of alternating sediments and cyanobacteria that take in carbon dioxide and release oxygen.

16. Precambrian Time: Archean Eon through Proterozoic Eon
Oxygen levels rose slowly as cyanobacteria and other early-life forms released oxygen.
Natural selection favored organisms that could tolerate or use oxygen.
The amount of ozone in the atmosphere increased.

17. Precambrian Time: Proterozoic Eon
The first invertebrate organisms, animals without backbones, appeared during the Proterozoic Eon.
These were called Ediacaran fauna, and looked similar to present-day jellies, worms, and corals.

18. Phanerozoic Eon: Paleozoic Era
The first appearance of fossils of organisms made from hard parts marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon.

19. Phanerozoic Eon: Paleozoic Era
Because hard parts fossilize easier, fossils are easier to find in Paleozoic rocks than Precambrian rocks.

20. Phanerozoic Eon: Paleozoic Era: Cambrian Period
The first period in the Paleozoic Era is called the Cambrian Period.

21. Phanerozoic Eon: Paleozoic Era: Cambrian Period
5 million years into the Cambrian Period, an event called the Cambrian Explosion occurred.
In a short amount of time, the number of animals with shells greatly increased.

22. Phanerozoic Eon: Paleozoic Era: Cambrian Period
Invertebrates such as sponges, jellies, and corals also evolved during the Cambrian explosion.
Changes in trilobite
body forms matched
changes in the
environment.

23. Phanerozoic Eon: Paleozoic Era: Cambrian Period
A well-preserved 5-inch trilobite specimen from Morocco that swam in the ocean during the Devonian Period roughly 400 million years ago (evolved for over 300 million years)

24. Phanerozoic Eon: Paleozoic Era: Ordovician and Silurian Periods
Throughout the Paleozoic era, the oceans contained a wide variety of invertebrate organisms, such as including corals and brachiopods.

25. Phanerozoic Eon: Paleozoic Era: Ordovician and Silurian Periods
10-cm. cockroaches, 74-cm. wingspan dragonflies were found on land in the Silurian Period.

26. Phanerozoic Eon: Paleozoic Era: Ordovician and Silurian Periods
Vertebrates, animals with backbones, evolved during the early Paleozoic era.

27. Phanerozoic Eon: Paleozoic Era: Ordovician and Silurian Periods
The first of these lived in the oceans.
Bony fish with thick fins supported by large bones and muscles

28. Phanerozoic Eon: Paleozoic Era: Ordovician and Silurian Periods
Plants began spreading onto land as well.
Early land plants were small and lived in moist areas because they could not move water to all their parts.

29. Phanerozoic Eon: Paleozoic Era: Pennsylvanian Period
In order to reproduce, amphibians had to return to the water to lay eggs.

30. Phanerozoic Eon: Paleozoic Era: Pennsylvanian Period
A new organism evolved that could lay its eggs on land.

31. Phanerozoic Eon: Paleozoic Era: Pennsylvanian Period
Amniotes laid water-tight eggs and could spend all their time on land.
Mammals, dinosaurs, and reptiles evolved from amniotes.

32. Phanerozoic Eon: Paleozoic Era: Pennsylvanian Period
Plants with vascular systems that could move nutrients between roots and leaves evolved and spread quickly.

33. Mass Extinctions
The Paleozoic Era ended with the late Permian Period extinction: 90% of marine and 70% of land species.

34. Mass Extinctions
260 million years ago, the uplifting formation of Pangaea, or ash and sulfur released from the Siberian Traps may explain the Permian extinction.

35. Mass Extinctions
We don’t know exactly what happened, but we know global temperatures rose.
Global
Temperature

36. Mass Extinctions
With most of the larger, predator-type animals going extinct, other organisms could increase in number, and expand around the world...

37. C iron in minerals quickly oxidized
8.2 Early Earth History A B C D
Which is not a characteristic of Earth’s early atmosphere during the Precambrian time?
A very little oxygen
B no ozone layer
C iron in minerals quickly oxidized
D organisms were exposed to ultraviolet rays

38. What were some of the first vertebrates? A brachiopods B trilobites
8.2 Early Earth History A B C D
What were some of the first vertebrates?
A brachiopods
B trilobites
C ediacaran fauna
D bony fish

39. What ended the Paleozoic era? A Ordovician extinction
8.2 Early Earth History A B C D
What ended the Paleozoic era?
A Ordovician extinction
B Devonian extinction
C Permian extinction
D Cambrian extinction

40. What caused oxygen levels to rise in Earth’s atmosphere? B C D
What caused oxygen levels to rise in Earth’s atmosphere?
A the presence of photosynthetic organisms
B the evolution of bacteria-eating organisms
C an increase in the ozone layer
D the evolution of organisms that could tolerate or use oxygen

41. The evolution of amniotic eggs allowed ___. B C D
The evolution of amniotic eggs allowed ___.
A the spreading of organisms into dry land
B the movement of organisms to shallow-water environments
C the evolution of amphibians
D organisms to live on land and lay eggs in the water

42. Which does not characterize the Cambrian explosion?
A an increase in small-shelled organisms
B the evolution of amniotes
C an increase in invertebrates
D an increase in large-shelled organisms

43. Events In Earth’s Past (6:11)

44. Early Earth Organisms Drawings
For the 2 eons and the 7 periods with a * after their name, draw and color 1 organism that could be found alive during that time.
text p. 326 and 328

45. Phanerozoic Eon Paleozoic Era Precambrian Time
mass extinction
Paleozoic Era
Permian Period *
Pennsylvanian Period *
Mississipian Period *
mass extinction
Devonian Period *
Silurian Period *
mass extinction
Ordovician Period *
Cambrian Period *
Precambrian Time
Proterozoic Eon *
Archean Eon *
Hadeon Eon