Canada’s Geologic HistoryChapter 11

Plates• The structure of the earth is similar to that of a

frozen lake; however, there a three important differences.•Earth’s plates (i.e. the ice on the lake) are made up of solid rock.•The “water” beneath the earth is actually very dense liquid rock that is heated by the earth’s core. •The movement of ice on the water is generally caused by wind, but the movement of Earth’s plates is due to heat currents that start in the core.

• There are TWO types of plates:1. Oceanic (water surface)2. Continental (Land surface)

• Uneven temperatures within the earth cause convection currents to move the plates

Earthquakes and Volcanoes• These natural disasters occur where there is

movement of Earth’s plates

• Picture the ice of the frozen lake is now broken up into huge plates that can be moved by wind and by currents in the water below.

• In some places ice plates (just like Earth’s plates) are pulled apart, while in others they are smashed together.

The Theory of Continental Drift• First proposed by Alfred Wegener in 1912• His theory Stated:•A super continent called Pangaea (meaning “all land”) once existed. Pangaea started breaking up into smaller continents about 200 million years ago and ‘drifted’ into their present positions.

Evidence to support his theory…• Fit of the continents – they fit like a puzzle.

• Fossil Evidence• Identical fossil evidence was found on different

continents. Therefore, the landmasses must have been joined together at some point.

• Rock type similarities• The exact same age and type of rocks were found on

various continents.

The issue was he couldn’t explain HOW the plates were moving and was ridiculed by many colleagues.

The Theory of Plate Tectonics• Proposed by J. Tuzo Wilson in 1968• His Theory states:• The outer crust consists of several individual segments

called ‘plates’, they are moving over a weak layer of hot rock • Movement is caused by energy created beneath the

Earth’s surface because of uneven temperatures.

PLATE MOVEMENT

divergencetransverse

convergence

DIVERGENCE

- plates move apart from one another- creates seafloor spreading

- located along the Mid-Atlantic Ridge

SEAFLOOR SPREADING

oceanic plate oceanic plate

CONVERGENCE

- plates move towards one another- creates mountains, or subduction

- located in the Pacific Ocean

TRANSVERSE

- Plates move past or beside one another, causing friction

- Located along the San Andres Fault line in California