Think about the following questions and be ready to give me an answer when we begin… 1. Why does the earth look the way that it does? 2. Earth vs. people – who wins, and why?

Chapter 4, Section 1 Landforms (part 1) Focus Question… 1. What physical processes inside Earth build up the land?

I. Forces below the Earth’s Surface Continue to push up the surface and break it apart Earth is composed of four layers At the center is the Inner Core - solid metal Outer core – mostly liquid metal Mantle – mostly solid Most of earth’s mass In this layer Crust – thin outer layer

Surface is bent and broken by hot spots in upper mantle and lower crust Magma (liquid rock) occasionally rises to surface Called lava when It breaks the surface

Plate Tectonics A theory that helps to explain how the world’s large landforms were created Earth’s crust divided into more than a dozen ‘plates’ Yellow indicates where earthquakes occur

Plates move very slowly No more than a few inches a year What would it be like if plates moved hundreds of feet per year?

Plates anywhere from 6 to 60 miles thick Thinner under oceans More dense (heavier rocks) Thicker under continents Less dense (lighter rocks) Thickest parts are under mountains

200 million years ago plates were together in a supercontinent called Pangaea Pangaea broke into smaller supercontinents Laurasia (N. America and Eurasia) Gondwanaland (everything else)

3 types of plate movement 1. Plates moving away from each other (divergent boundary)

Crust moves upwards and forms a chain of mountains. Why? Called mid-ocean ridge Steep and jagged because they don’t erode like mountains on land Found on every ocean floor

Islands occur where mid-ocean ridge rises above water Surtsey, off the southern coast of Iceland, 16 days old (1963)

2. Plates pushing against each other (convergent boundary) A trench forms when a heavier plate dives below a lighter plate. Which plate is heavier, the ocean plate or the continental plate? Some are 600 miles long and 60 miles wide Up to 7 miles deep (deepest part of ocean)

If one plate is a lighter continental plate… The lighter plate crumples and forms a mountain range The heavier plate sinks and forms a trench offshore Andes Mtns in S. America a good example Looking towards S. Pole Andes Mtns Trench

If both are lighter continental plates… No trenches form The Earth’s crust crumples like fenders when two cars slowly collide, forming a high mountain range Himalayas between India and China a good example

What happens to rocks when the crust moves? When rocks bend, the result is a FOLD

When rock layers break and move apart, the result is a fault

Earthquakes are caused by movement along fault lines

3. Plates sliding past one another (transform fault) Low mountains may form The San Andreas fault in California a good example Lots of earthquakes here Dotted line indicates fault line