1. Chapter 22 – The Precambrian Earth
The Precambrian covers almost 90% of the entire history of the Earth. 
Chapter 22 – The Precambrian Earth
Produced by
S. Koziol

2. 22.1 – The Early Earth Objectives:
Describe the evidence used to determine the age of the Earth.
Understand why scientists theorize that the early Earth was hot.

3. Zircon
Zircon is a stable mineral that commonly occurs in granite.

4. Oldest known mineral The oldest known mineral on Earth is zircon.
From the Jack Hills region of Australia a billion years old ± 6 million years.

6. Asteroid
Asteroid are metallic or silica-rich objects that orbit the Sun between the orbits of Mars and Jupiter.

7. Meteorite
Meteorite is a meteor that has fallen to and reached the surface of Earth.

8. Why do scientists consider the age of meteorites when they try to estimate the age of Earth?
 Most astronomers agree that the solar system, including Earth, formed all at once, and therefore Earth and meteorites should be about the same age.

9. Earth’s Current Estimated Age
4.54 ± 0.05 billion years 
This age is based on evidence from radiometric age dating of meteorite material and is consistent with the ages of the oldest-known terrestrial and lunar samples.

10. Why scientists theorize that the early Earth was hot.
 The combined effects of radioactive decay, asteroid and meteorite bombardment and gravitational contraction made for a hot and inhospitable beginning for Earth.

11. 22.2 – Formations of the Crust and Continents
Objectives:
Explain the origin of Earth’s crust.
Describe the formation of the Archean and Proterozoic continents.

12. Earth’s earliest crust
Earth’s earliest crust likely formed as a result of the cooling of the uppermost mantle.
Earth’s crust first formed at least 4.4 billion years ago, just 160 million years after the formation of our solar system.

13. Microcontinents Both are early Earth Continents. Laurentia
Laurentia was an ancient continent that formed the core of modern-day North America.
A microcontinent is a small piece of continental crust
Laurentia, also called the North American craton

14. The craton
The buried and exposed parts of a continental shield together compose the craton, the stable core of a continent.
Laurentia, also called the North American craton

15. Laurentia
Laurentia - Ancient continent that contained core of modern-day North America

16. Precambrian shield
Precambrian shield is the Continental cores of Archean and Proterozoic rock
These are the nuclear (beginning) area of Precambrian rocks present in each of the continents.

17. Canadian shield
Canadian shield - The Precambrian shield in North America.

18. Precambrian vs. Canadian
These are the nuclear (beginning) area of Precambrian rocks present in each of the continents.
Precambrian
Canadian
A Precambrian shield is a continental core of Archean and Proterozoic rock.
Canadian Shield is the Precambrian shield specifically of North America.

19. 22.3 – Formation of the Atmosphere and Oceans
Objectives:
Describe the formation of Earth’s atmosphere and oceans.
Identify the origin of oxygen (O2) in the atmosphere.
Explain the evidence that oxygen (O2) existed in the atmosphere during the Proterozoic.

20. Outgassing
The process by which volcanoes vent water vapor, carbon dioxide, nitrogen, and other substances is called outgassing.

21. Cyanobacteria
are tiny, threadlike photosynthetic organisms.

22. Stromatolite
Stromatolite is a mat or mound composed of billions of cyanobacteria.

23. Cyanobacteria
Cyanobacteria use the process of photosynthesis to produce energy, and oxygen is given off as a waste product.

24. Stromatolites
The ozone layer that filters ultraviolet radiation originated from oxygen produced by stromatolites.

25. Why was the earliest atmosphere eventually replaced by oxygen and nitrogen gases and carbon dioxides?
Both helium and hydrogen gas have small masses. Earth’s gravity was not great enough to keep them from escaping into space. Gases with higher masses like carbon and nitrogen are unable to escape Earth’s gravity and eventually replaced the helium and hydrogen.

26. Banded iron formation (BIFs)
Banded iron formation - Deposit consisting of alternating bands of chert and iron oxide

27. Red bed
Red bed - Sedimentary rocks younger than 1.8 billion years that are colored by the iron oxides in them
Banded iron formation, Karijini National Park, Western Australia

28. Banded Iron vs. Red Bed Banded iron (BIFs) Red bed
A banded iron formation is a deposit that consists of alternating bands of chert and iron oxides.
Formed underwater and in an oxygen-poor environment.
A red bed is a rock younger than 1.8 billion years that is rusty red in color as a result of the presence of iron oxides. Formed in an oxygen-rich environment. Red beds were formed on land, and not under the sea as the BIFs were.

29. 22.4 – Early Life on Earth Objectives:
Describe the experimental evidence of how life developed on Earth.
Distinguish between prokaryotes and eukaryotes.
Identify when the first multicellular animals appeared in geological time.

30. Hydrothermal vent
hydrothermal vent - Hot water vent at volcanic seafloor rift

31. Amino acids
amino acids - Building blocks of proteins

32. During the Archean
Miller and Urey demonstrated that the basic building blocks of life were most likely present on Earth during the Archean.
Heat, cyanide, and certain clay minerals can cause amino acids to join together in chains.

33. During the Archean
Amino acids have been found in the waters of hydrothermal vents, suggesting that proteins and nucleic acids could have formed there during the Archean.

34. Does the Miller and Urey’s experiment prove that life originated in such a liquid?
No. The experiment merely demonstrates that some of the molecules found in living things can arise under conditions that may be like those of early Earth.

35. Single-celled organisms
Single-celled organisms that belong to the Kingdom Monera are prokaryotes.

36. Prokaryote
An organism composed of a single cell that does not contain a nucleus and is the simplest kind of cell is a prokaryote.

37. Eukaryote vs. Prokaryote
They both:
have DNA as their genetic material
membrane bound
have ribosomes
basic metabolism
amazingly diverse in forms
Prokaryote
Eukaryote
A prokaryote is a simple organism composed of a single cell, which does not contain a nucleus, while
A eukaryote is an organism that is composed of multiple cells, which contain nuclei and are more complex and larger than those of prokaryotes.

38. Ediacaran fauna
Ediacaran fauna are fossils of soft-bodied Proterozoic organisms

39. Varangian glaciation
Varangian glaciation - Glacial event that occurred between 700 and 800 million years ago.
Varangian glaciation

40. Widespread glaciation at end of the Proterozoic
A major extinction of acritarchs occurred near the end of the Proterozoic, in which widespread glaciation may have played a critical role.