1. In your databooklet
The timeline that we will follow is located on page 4 of your databooklet.
Please note that the timeline is not to scale
E.g. the Precambrian era should be about 500 times longer than the Cenozoic era

2. Precambrian Era the first major section of geological time,
from the origin of Earth (~4.5 billion years ago) up to 590 million years ago
During this era, the rocks that act as the foundation of our continents were formed
During the Precambrian Era the Canadian Shield was formed

3. Precambrian Era
From deposited rock, geologist determine a stratigraphic sequence
a arrangement of rocks that provides a chronological record of a region’s geological history.
They use this sequence to relatively date rock and fossil samples.
The Law of Superposition states that higher strata in a sequence of rock layers are younger than lower strata.

4. Precambrian Era Some anomalies to the law of superposition include
Intrusions
a body of rock that forms from the invasion of magma into a pre-existing rock formation
Outcroppings
When a rock layer that is normally underground becomes exposed
Examples of outcrops include:
Mountain rock faces
Canyon walls
River valley cliffs
Coastal cliffs

5. Precambrian Era
Early conditions on Earth were not very conducive to life
frequent volcanic eruptions
poisonous gases in atmosphere
oceans were extremely hot – over 100oC.
The only living thing was Archaea – bacteria-like organisms.

6. Precambrian Era
Cameron Falls in Waterton Lakes National Park is an example of are an outcrop formed during this era that also shows evidence of this early life form.
important because they are also the site of stromatolites, Alberta’s oldest fossils

7. Stromatolites
Stromatolites are trace fossils, meaning they are imprints formed by the activity of a previously living organism
other examples of trace fossils include footprints, burrows and feeding marks
they are the indirect evidence that cyanobacteria were inhabiting mud flats at the shore of a warm, tropical sea about 1.5 billion years ago

8. Stromatolites
Stromatolites make excellent index fossils, because they are very distinctive, and only existed for a limited period of time.
Index fossil are used to determine the relative age of rock, as the rock surrounding the recognizable fossil will be the same age as the fossil itself.
They can also be used to match stratigraphic sequences, from different locations.

9. Stromatolites
Stromatolites were once responsible for the production of oxygen in our atmosphere, enabling other life forms to develop
stromatolites are now extremely rare and only found on a few places on earth

10. Cyanobacteria: A Source of Oxygen
Cyanobacteria are single-celled bacteria, thought to be the Earth’s first photosynthetic organisms
by growing and dying one layer on top of the other, the cyanobacteria slowly deposited layer after layer of calcium carbonate
the main ingredient of limestone, chalk, and your bones
stromatolites are the remains of the calcium carbonate layers, not the cyanobacteria themselves - this is what makes stromatolites an example of a trace fossil

11. Precambrian Era
Direct evidence, such as fossil imprints found in the Rocky Mountains, reveals that near the end of the era, stromatolites now shared their shallow waters with multicellular creatures , such as:
small jellyfish,
worm-shaped animals
early plants

12. The Cambrian Explosion
The Cambrian Explosion refers to the dramatic increase in the variety of organisms in a relatively short geological timeframe that occurred at the beginning of the Paleozoic era

13. The Cambrian Explosion
Why did so much biological diversification occur at this time?
Some researchers have suggested that the atmospheric oxygen levels finally reached a concentration high enough to support the more active metabolism of these mobile animals.
While scientists continue to investigate possible answers to this question, it is remarkable that life on Earth for the past half-billion years seems to involve variations on the basic designs that first emerged from the Cambrian Explosion.

14. The Cambrian Explosion
The Burgess Shale, is considered by many scientists to be the most important source of Cambrian fossils on Earth.
the Burgess Shale has been designated by the United Nations as a World Heritage Site.
Geologists have evidence that more than 500 million years ago, the organisms now fossilized in the Burgess Shale were inhabiting a shallow area close to the shore of a tropical sea.

15. The Cambrian Explosion
The animals in the Burgess Shale are from both warm shallow-water creatures and deep-water organisms.
These animals are all found in soft mud.
Evidence suggests that a series of underwater mud avalanches carried the organisms over the cliff edge, where they were then buried within layers of mud.
The hard body parts of these organisms were fossilized in much the same way as other Cambrian fossils, but what makes the Burgess Shale unique is that the soft body parts of these animals were also preserved.

16. The Cambrian Explosion
This was due to the fact that the mud was comprised of such tiny particles that the organisms caught in the mud were immediately encased in mud, which likely had low concentrations of oxygen.
The result was that decay was limited and the effects of scavengers were eliminated.

17. Assignment Complete: Investigation: The Early Atmosphere(pg 304)
Q’s 1 ,3, 6 & 8 (pg 305)
Investigation: Matching Rock Strata from Different Locations (pg 311)
Q’s 2, 4, 8, 9, 10(pg 313)
Q’s 2-5 (pg 335)

18. Investigation pg. 304 Read the background information on page 304
What does banded iron tell you about oxygen in Earth’s atmosphere during the Precambrian Era?

19. Investigation pg. 304 (solution)
1. Identify the likely source of oxygen required to form the iron (III) oxide found in red layers of banded iron formations. Answer: The source of oxygen likely came from cyanobacteria. Cyanobacteria produced oxygen through the process of photosynthesis.

20. Investigation pg. 304 (solution)
2. The oldest banded iron formations are 3.8 billion years old. Rock layers below these do not contain iron (III) oxide.
a) Infer what this suggests about the oxygen level in Earth’s atmosphere before the banded iron was deposited.
Answer: It suggests that O2 was not present.

21. Investigation pg. 304 (solution)
b) Banded iron formations of less than 1.8 billion years old are extremely rare. Sedimentary rock layers deposited on top are all rich in iron oxide, but there is no evidence of the striped iron bands. Conclude what this evidence suggests about atmospheric oxygen after the banded iron was deposited.
Answer: Starting from 1.8 billion years ago, significant levels of oxygen were consistently present, therefore the rock was entirely oxygen rich not just in bands.

22. Investigation pg. 304 (solution)
c) Describe the atmospheric oxygen levels during the time of banded iron formations.
Answer: During the time of banded iron formations from 1.8 billion years ago to 3.8 billion years ago, significant levels of oxygen were present only at certain times (the red bands). At other times, oxygen was unavailable (the grey bands).

23. C1.4 – Creating Theories & Getting a Handle on Time

24. Forces of Catastrophe
Catastrophism: theory from the 18th century that cites major, violent disasters as the main forces that shape the Earth
include processes of a different type or intensity than those observed in the present
the ones we have presently are too weak and slow for such change

25. Catastrophic Theories
These theories may have dominated geological discussions for over a hundred years because they fit in with the common belief that the Earth was only approx years old
However, observing these catastrophic events today, it is hard to imagine that these produced the geography that we see