Deep Time  The theory that Earth has a long history of development & change lasting billions of years Deep time began with the Precambrian Era

1.1 The Long Beginning  The Precambrian Shield  Strange red belt of granite rock called “Slave Granite” commonly known as the Canadian Shield  2 billion years old, formed in the Precambrian Era  Makes up more than half of Canada’s land mass (including most of Ontario & Quebec) Precambrian or Canadian Shield

Precambrian Era – 1 st major section of geological time, lasting from the origin of Earth 4.5 billion years ago up to 590 million years ago Outcrop – when a rock layer that is normally underground is exposed e.g. Slave Granite precambrian-video.htm

Earth is like an Egg…  It’s internal structure is over 6500 km to the centre of the Earth  The deepest wells are 13 km deep & our deepest mines are only 4 km  Earth can be separated into layers according to their densities  The densest material sinks to the centre, while least dense material floats on the surface

The Core  You can think of the core of Earth as the yolk of a hard boiled egg  Core – innermost (most dense) layer of Earth  Made of nickel & iron Has 2 parts: 1) solid inner core AND 2) liquid outer core The liquid outer core spins with the rest of the planet causing Earth’s magnetic field

The Mantle  The layer of Earth between the crust & the core  Can be compared to the white of a hard boiled egg  Is a solid layer that makes up about 80% of Earth’s volume  Extreme heat & pressure within the mantle cause zones of rock to behave as a plastic  Plastic – substance with properties of a solid that can flow under pressure  E.g. squeezing toothpaste out of a tube

Parts of the Mantle Asthenosphere  The uppermost layer & most plastic part of the mantle E.g. magma from asthenosphere rises up in form of volcanoes Mesosphere  Rest of mantle beneath the asthenosphere  More rigid Lithosphere  Earth’s outermost rigid layer of rock  Similar to the shell of an egg  Includes solid oceanic crust & continental crust that float on the atmosphere

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Motion in the Mantle  It’s impossible to directly observe layers below the lithosphere  Scientists use indirect evidence from events (e.g. earthquakes) to develop theories about Earth’s structure

One Theory…Convection  Pushes & pulls on the Earth’s crust cause it to crack, tear & move  Scientists believe huge convection cells within the mantle push & pull on Earth’s crust  The lithosphere can be thought of as a cracked shell that makes up a mosaic of rigid pieces called crustal plates Large pieces of continental OR oceanic crust that float & slowly move atop the atmosphere **Crustal plates move a few cm per year & this movement forms new oceans & mountain ranges**

Convection

Dynamic Crust  Plate tectonics- theory that the lithosphere consists of crustal plates that slowly move across Earth’s mantle (via convection) & interact at their boundaries  Sea floor spreading – when crustal plates separate mid-oceanic ridges  Means the youngest rocks on oceanic plates are located are located closest to the spreading centre

Paleomagnetism  The study of magnetic properties of rock formed in a past geological era Sections of the sea floor have rock with their magnetic fields pointing in the opposite direction. This indicates that the magnetic field of the Earth has reversed more than once in the past several million years.

Slave Granite  Geologists believe granite was formed at the collision site of 2 continental crustal plates 2 billion years ago  Both plates welded together, pushing up huge rock wrinkles to form mountain ranges  granite was formed & then pushed up

Homework  Read p  Practice p. 299 #2 (Copy Chart)  Questions p. 301 #1-7