GEOLOGY

DEEP TIME: the theory that Earth has a long history of development and change lasting billions of years TIME BOGGLE: If we represented the Earth’s history as just 24 hours, 400 generations of people would take only 0.2 seconds of that day! Go to pg. 295 and read “Try this Activity”. You need to get into groups of 2-3 and you will have the next 15 min to complete this activity and the Questions #1-4 Read the Chapter Intro on pg. 294

When is the PRECAMBRIAN ERA? (from your timeline activity) ROAD MAP ACROSS ALBERTA When is the PRECAMBRIAN ERA? (from your timeline activity) The first major section of geological time, lasting from the origin of the Earth 4.5 billion years ago up to 590 million years ago This strange red belt of granite rock is called the Slave Granite. At two billion years old, it is among Alberta’s oldest rocks. The Slave Granite is part of the Precambrian Shield, often called the Canadian Shield, which was formed in the Precambrian Era. The Precambrian (Canadian) Shield is what’s left of the original North American continent, which formed four billion years ago.

The Canadian Shield is one of eight main physiographic regions of Canada, but in Alberta you would have to dig several thousand meters to reach this basement rock. So the Slave Granite is a special case we call an outcrop.

When a rock layer that is normally underground in exposed, like the Slave Granite, it is called an outcrop. Other examples are rock faces, canyon walls, river valley cliffs and coastal cliffs.

Earth is like an Egg The CORE of the earth is like the YOLK of an egg - The core is the densest layer and is made of nickel and iron - The Egg Example isn’t perfect because the Earth’s core has two parts: a SOLID inner core a LIQUID outer core (spins with the rest of the planet and induces Earth’s magnetic field)

Earth is like an Egg The MANTLE of the Earth is like the WHITE of an egg The mantle is the solid layer comprising 80% of the Earth’s volume The extreme heat and pressure here causes the mantle to behave as a plastic A substance with the properties of a solid than can flow under pressure) E.g. Squeezing toothpaste out of a tube

Earth is like an Egg … so far… MANTLE INNER SOLID CORE OUTER LIQUID CORE

Earth is like an Egg … so far… MANTLE But we also divide the mantle into two parts: Asthenosphere – the uppermost layer of the mantle (more plastic) i.e. magma rising out of volcanoes is from the asthenosphere Mesosphere – the part of the mantle beneath the asthenosphere (more rigid)

Earth is like an Egg … almost there… The Lithosphere is like the shell of the egg. It includes the solid oceanic crust and the continental crust that float on top of the asthenosphere.

Lithosphere – includes both the continental crust and the oceanic crust Floats on top of the asthenosphere

Earth is like an Egg … finally there… Lithosphere } Asthenosphere Mantle Mesosphere Solid Inner Core Liquid Outer Core

SUMMARY Read pg. 298 and fill in the missing information Earth’s Layers Density Description Thickness atmosphere least dense                 most dense gaseous 300 km lithosphere solid most rigid layer 75 km to 125 km mantle asthenosphere least rigid or most plastic layer of mantle 225 km to 275 km mesosphere more rigid than uppermost layer of 2550 km core outer core liquid 2260 km inner core 1220 km Read pg. 298 and fill in the missing information

Motion in the Mantle Like French Onion soup…. Nuclear decay deep in the core radiates heat Heat moves up toward the cheesy crust then cools and sinks again We call this a Convection Cell

Convection Cells Warm, less dense material rises while cooler, more dense material descends forming one or more convection cells to distribute thermal energy. Convection VIDEO *

Why does convection matter? The process of convection within the mantle pushes and pulls on the Earth’s solid crust. But the earth isn’t like a single rigid layer on an egg, rather like a cracked shell of crustal plates

Crustal Plates Large pieces of continental crust or oceanic crust that float and move atop the asthenosphere (the plastic part of the mantle)

So how are plates created? SEA-FLOOR SPREADING Magma is pushed up from the mantle at mid-ocean ridges Magma cools and becomes rock Process continues pushing the older rock away from the ridge So where is the youngest rock in the oceans? Closest to the mid-ocean ridges ANIMATION

What do the crustal plates do? They actually move at the rate your fingernails grow (a few cm a year) They can: Rift apart and make new oceans Collide together and make mountains Slide over one another and send one plate down into the mantle to be melted again (Subduction) SUBDUCTION VIDEO

What does this all lead to… Plate Tectonics: the theory that the lithosphere consists of crustal plates that slowly move across Earth’s mantle and interact at their boundaries the process in which crustal plates are driven by convection currents or hot material from within the mantle.

So what evidence did we have that led us to the theory of Plate Tectonics? Researchers found that sections of the sea floor have rocks with their magnetic fields pointing in the opposite direction This indicates that the magnetic field of Earth has reversed more than once in the past several million years. Paleomagnetism: the study of the magnetic properties of rock formed in a past geological era

Because the poles are lined up in opposite directions, and are mirror images on either side of the ridge, this indicates that the Earth’s poles have reversed more than once in the past several million years. Paleomagnetism (the study of magnetic properties of rock) was one of the strongest pieces of evidence for sea floor spreading and plate tectonics

Let’s go back to the Slave Granite Why do we have exposed Precambrian (Canadian) Shield in a prairie area? The mountain ranges that once stood tall have long since eroded. However the slave granite remains as some of the oldest rock in Alberta. This happened billions of years ago. Because it was created by two plates pushing together. They were equal in density so one couldn’t slide underneath the other. Instead, both plates welded together, pushing up to form mountain ranges.

SUMMARY Well let’s let Bill Nye sum it all up for us

Now it’s your turn… Complete questions pg. 301 # 1-7