Plate Tectonics

Plate Tectonics

Form 1 Geography

Quick Review

Layers of the Earth

Multiple Choice

Which of the following is the innermost layer of the Earth?

• Core

• Atmosphere

• Mantle

• Crust

Multiple Choice

True or False: The Earth's crust is thicker than the inner layers.

• True

• False

Multiple Choice

What are the two types of crust?

• top crust,bottom crust

• oceanic crust, continental crust

• water,land

• none of the above

Multiple Choice

True or False:

The Earth's thin shell of hard rock is called the crust.

• True

• False

History of Plate Tectonics

History of plate tectonics

• Geographers and geologists have always wanted to explain how the world works and why it looks the way it does.

• They came up with several theories in the past.

• Catastrophism

• Uniformitarianism

• Global Cooling Theory

Catastrophism

• Scientists thought the world was shaped by sudden natural disasters or catastrophes.

• One example of this was work done by Abraham Ortelius in 1596, in his Thesaurus Geographicus. 

• This theory was the leading one for many years.

Multiple Choice

True or False:

Catastrophism was a popular scientifc theory for a very long time.

• True

• False

Uniformitarianism

• "The present is the key to the past."

• Based on James Hutton's "uniformitarian principle".

• All modern geologic processes happened in the past, and can be used to explain them.

• This is the foundation of modern geology.

Multiple Choice

Uniformitarianism is the key to which modern science?

• Geology

• Geography

• Biology

• Chemistry

Multiple Choice

The main principle of uniformitarianism states that the "___ is key to the ___."

• future, past

• past, present

• present, past

• past, future

Global Cooling - Contracting Earth Theory

• Proposed by American geologist James Dwight Dana.

• The Earth is a big ball of molten metal in space.

• As it cooled, heavier metals (Fe) sank to the center and lighter ones (Al) rose to the surface.

• This made some parts move upward to form mountains, or downward to form ocean basins.

Modern Tectonic Theories

Continental Drift Theory

• In 1912, a geologist named Alfred Wegener, published a paper talking about his theory of continental drift.

• This theory was not received at the time by other scientists due to a lack of evidence.

Continental Drift Theory

• The world was initially a supercontinent called Pangaea.

• This continent eventually broke into 2 smaller ones called Laurasia and Gondwanaland.

• After a while, these continents broke up into smaller pieces and started to drift further apart.

Multiple Choice

What does the theory of continental drift state?

• The continents were once joined in a super-continent and have moved over time

• Continents are stationary and do not move

• The Earth is broken into lithospheric plates that move due to convection currents

• none of the above

How do we Know Plate Tectonics is Real?

Listen and write the answers to the following questions:

1. What did Wegener call his idea?

2. Give one reason why Wegener thought his ideas were right.

3. Did other scientists agree with Wegener?

4. How quickly are the mid-Atlantic and North American plates moving away from each other?

Wegener's Evidence of Plate Tectonics

• The continents “fit together like pieces of a jigsaw puzzle”.

• The Earth’s geologic record shows that rocks with similar composition can be found all over the world. E.g. coal in Pennsylvania with the same composition as coal in Poland and Germany.

• Fossils can be found in different parts of the world e.g. a fossil of a plant in the Appalachians in the US and the Atlas Mountains in Morocco.

• Mountains on the Earth’s surface are not all the same age.

Why was his theory rejected?

• He couldn’t prove how the continents moved - he thought it was due to the rotation of the Earth.

• He couldn’t explain how the continental crust moved through the oceanic crust - he thought it was like a glacier.

• Scientist of the time thought that the Earth’s crust was formed by the contraction of the surface as it cooled.

Improvements to Wegener's theory

• The basis of modern plate tectonic theory was discovered by Arthur Holmes in 1929.

• His suggestion was that the mantle heats and cools in a process known as convection - and that moved the crust.

• Holmes’ theory didn’t gain popularity until 1960, when geologist were able to identify features such as seafloor trenches.

• Harry Hess (1962) and R. Deitz (1961) created the theory of seafloor spreading and helped shape our understanding today.

Multiple Choice

The process of movement of the mantle caused by heating and cooling is...

• Radiation

• Conduction

• Convection

• Contraction