1. Science 20 Unit C
Geology

2. Unit C The Changing Earth
C1.1 - How do we know what we know?

3. Deep Time
The theory that the Earth has a long history of development and change lasting billions of years
Scientists generally agree that the Earth is about 4.5 billion years old
As we discuss the events that shaped, and continue to shape our world, you may be tempted to ask the question: “how do we know?”

4. Time Boggle
If you think of Earth’s entire deep-time history as happening in just 24 hours, those 400 generations would have taken only the last 0.2 seconds of that day, which is virtually an instant in geologically time.

5. Changing Earth’s Structure
Major changes in the Earth’s structure take millions of years to occur, yet all of human history has occurred in the last 100,000
These changes could not have been directly observed.
Also, it is actually not possible to “dig a hole to China,” so much of what we know about the structure of the whole Earth is merely theory.

6. The Changing Earth Three major topics will be addressed in this unit:
How the physical structure of the Earth has changed
How the conditions needed to support life, such as climate, have changed
The impact of these two changes on the type of life found on Earth

7. Changing Earth’s Structure
We can, however, make direct observations about how the Earth’s surface has changed over shorter periods of time, and use that to extrapolate deeper and more long term
Surface changes include:
erosion
volcanic eruptions
deposition
changing tides
water levels & glacier changes

8. Changing Earth’s Structure
In addition, we have evidence to indicate that the Earth’s crust has moved, and continues to move
formation of mountains and canyons
earthquakes

9. The Long Beginning
C1.1

10. The Precambrian Shield
The strange red belt of granite rock is now called the Slave Granite.
The Slave Granite is part of the Precambrian Shield, often called the Canadian Shield.
It was formed in the Precambrian Era
The first major section of geological time, lasting from the origin of Earth 4.5 billion years ago up to 590 million years ago.

11. The Precambrian Shield
Is what is left of the original North American continent.
It makes up more than half of Canada’s land mass, including most of Ontario and Quebec.

12. The Precambrian Shield
In Alberta you would have to dig several thousand metres below the surface to reach this rock.
When a rock layer that is normally underground is exposed, like the Slave Granite, it is called an outcrop.

13. Granite
If you look at granite you can see large mineral crystals of various shapes and sizes peppered throughout.
Some of these minerals can be formed only under extremely high temperatures of 900 – 1000o C and very high pressures

14. Earth is Like an Egg
Earth can be separated into layers that are arranged according to their densities.
The densest layers sink to the centre and the least dense float on the surface.

15. The Yolk = the Core Solid inner = 1220 km Liquid outer = 2260 km
The innermost layer of Earth that consists of a solid inner core and a liquid outer core.
The core is the densest layer and is made of nickel and iron
The liquid core spins compared with the rest of the planet.
This induces Earth’s magnetic field.
Solid inner = 1220 km
Liquid outer = 2260 km

16. Egg White = the Mantle The layer of the Earth between crust and core.
Makes up about 80% of Earth’s volume.
The extreme heat and pressure within the mantle cause zones of rock to behave as a plastic.

17. The Layers of the Mantle
The asthenosphere is the upper most layer of the mantle.
It is the least rigid and most plastic part of the mantle.
The plastic nature can be seen when magma from the asthenosphere rises up in the form of volcanoes.
Asthenosphere = 350 km

18. The Layers of the Mantle
The rest of the mantle beneath the athenosphere is more rigid.
This layer is known as the mesosphere.
Finally there is the lithosphere which is like the shell of the egg.
The lithosphere includes the solid oceanic crust and continental crust that float on the athenosphere.
Mesosphere = 2550 km
Lithosphere = 75 km
Oceanic crust = 4-7 km

19. Motion in the Mantle
In the mantle there are convection currents – hot magma (melted rock) expands, rises, cools when it reaches the crust, and then falls. This causes crustal plates to move.
A crustal plate is a large piece of continental crust or oceanic crust that floats and slowly moves atop the asthenosphere.
As a result the Earth is more like an egg with a cracked shell.

20. The main features of plate tectonics are:
The Earth's surface is covered by a series of crustal plates.
The ocean floors are continually moving, spreading from the center, sinking at the edges, and being regenerated.

21. Convection Currents
Convection currents beneath the plates move the crustal plates in different directions.
The source of heat driving the convection currents is radioactivity deep in the Earths core

22. Evidence of Plate Tectonics
Paleomagnetism (study of the magnetic properties) in trenches
Mountains, folded layers of soil & rock occur
Volcanoes & hot springs occur
Mid Oceanic ridges & ocean trenches occur

23. Types of Plates
Divergent boundaries -- where new crust is generated as the plates pull away from each other. Site of ocean ridges & valleys (rifts).

24. Types of Plates
Convergent boundaries -- where crust is destroyed as one plate dives under another. Site of mountain ranges, valleys & volcanoes

25. Types of Plates
Transform boundaries -- where plates slide horizontally past each other. Site of earthquakes

26. Types of Plates
Plate boundary zones -- broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.

27. Slave Granite
Geologists think that the Slave Granite rock was formed at the collision site of two continental crystal plates about two billion years ago.
Since these plates had equal densities, one plate couldn’t slide under the other.
In this case, both plates welded together, pushing up huge rock wrinkles to form mountain ranges.
At the site of the weld, the granite was formed and then pushed up.
The mountain ranges that once stood tall have long since eroded.
However, the Slave Granite remains as some of the oldest rock in Alberta.

28. Assignment
1.1 Questions
Pg. 301#1-7

29. Early Life
C1.2

30. Cameron Falls
Contains an outcrop of Alberta’s oldest sedimentary rock.
Rock formed from many layers of pre-existing rock or organic matter.
You can see layer upon layer of sediment compressed into solid rock.
The properties of the sediments, and the fossils preserved in each strata, provide information about they type of environment that existed when they were deposited 1.5 billion years ago.
Fossil – the evidence or remains of early life preserved in Earth’s crust
Strata – the layered bands within sedimentary rock

31. An Ancient Coast
Sedimentary rock formations in the Rocky mountains indicate that several large rivers deposited sand, clay and silt into an ocean
A sandwich of sedimentary rock 11 km thick is currently evident.

32. Life Gets Started
Some scientists think that single celled organisms where the earliest form of live (3.8 million years ago.) Archaea bacteria, which can live in water at 150 C are though to be the relatives of this bacteria.
Next came the cyanobacteria which deposited calcium carbonate (limestone). They created stromatolites (layered structures) which we call trace fossils (remains left by an organism.)

33. Hot Oceans
Early Earth was filled with the frequent volcanic eruptions and poisonous gases
The oceans were very hot, over 100o C.
One organism that tolerate the heat and poisonous gas was Archaea.
They were first found in the boiling waters of a hot spring in Yellowstone National Park.
Deep-sea thermal vents release intense volcanic heat and hydrogen sulfide gas.
Archaea thrives in these conditions and feed on the hydrogen sulfide which is poisonous to humans.
This group of extremist life forms may be the closest living evidence of Earth’s earliest life.

34. Source of Oxygen
Cyanobacteria contained calcium carbonate which traps the suns energy to make glucose (food) and oxygen. This process is called photosynthesis.
PHOTOSYNTHESIS:
Carbon Dioxide + Water  Glucose + Oxygen

35. Other Evidence of Oxygen
Red & gray banded iron can be found in sedimentary rock.
Gray bands have iron only.
The red bands are iron (III) oxide which must of reacted with oxygen. (see reaction below.)
4Fe3+(aq) + 3O2(g)  2Fe2O3(s)

36. Snowball Earth
Late in the Precambrian Era, life barely survived during the most significant ice age ever.
Ice covered most of the planet for nearly ten million years.
This is often called Snowball Earth.
Some scientists believe that the stresses placed upon organisms as the result of changes in their habitat during this deep freeze, and the thaw that followed, may have resulted in an explosion in species diversity that led to the first complex creatures.

37. Assignment
Practice questions
1.2 Questions
Pg. 305 #1-8