Plate Tectonics Liz LaRosa for use with my Science Class http://www.middleschoolscience.com 2009

Earth’s Layers The Earth's rocky outer crust solidified billions of years ago, soon after the Earth formed. This crust is not a solid shell; it is broken up into huge, thick plates that drift atop the soft, underlying mantle.

The Crust Outermost layer 5 – 100 km thick Made of Oxygen, Silicon, Aluminum

The Mantle Layer of Earth between the crust and the core Contains most of the Earth’s mass Has more magnesium and less aluminum and silicon than the crust Is denser than the crust

The Core Below the mantle and to the center of the Earth Believed to be mostly Iron, smaller amounts of Nickel, almost no Oxygen, Silicon, Aluminum, or Magnesium

Tectonic Plates

Plate Tectonics Greek – “tektonikos” of a builder Pieces of the lithosphere that move around Each plate has a name Fit together like jigsaw puzzles Float on top of mantle similar to ice cubes in a bowl of water

Continental Drift In 1912 a German meteorologist named Alfred Wegener noticed that the continents fit together like puzzle pieces. He proposed that the continents were joined together in the past, in a large land mass called Pangaea, Greek for “all Earth” Fossils of the same plants and animals are found on different continents. http://members.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml

Over time, the continents drifted apart – Wegener named his theory “Continental Drift”.

Evidence of Pangea

He supported his theory with four pieces of evidence. 1. Puzzle like fit of continent edges http://maps.google.com

2. Matching fossils of plants and animals on once connected land areas. Fossils of Glossopteris are found in Permian rocks of South Africa, India, Australia, South America, and Antarctica

3. Rock similarities and ages Mountains in South America and Antarctica are believed to have formed as part of the same mountain chain.

4. Climate evidence (Glacial evidence in Africa, South America, Australia, and India and tropical plant fossils in Arctic areas) Fossils found in Antarctic soil indicate that the now frigid continent was once lush with trees and ferns, and home to dinosaurs, amphibians, and later, marsupials.

Wegener’s theory made sense, but no one wanted to accept it until they knew HOW the continents moved.

Continental Drift Whiplash In the 1960’s, a Princeton University scientist named Harry Hess, discovered how the continents drifted. Continental Drift Whiplash

Seafloor Spreading Magma in the mantle rises and pushes the plates apart, forming new oceanic crust. http://education.sdsc.edu/optiputer/flash/seafloorspread.htm

How Plates Move http://pubs.usgs.gov/gip/dynamic/unanswered.html

Sea Floor Spreading Mid Ocean Ridges – underwater mountain chains that run through the Earth’s Basins Magma rises to the surface and solidifies and new crust forms Older Crust is pushed farther away from the ridge

Seafloor Spreading causes Continental Drift

Supporting evidence of seafloor spreading 1. Magnetic iron particles record the time of the rock formation. http://www.wwnorton.com/college/geo/egeo/flash/2_3.swf 2. Rocks farther away from the opening age at the same rate on both sides. http://www.wwnorton.com/college/geo/egeo/flash/2_5.swf

A map of the ocean floor provides even more evidence http://maps

Iceland shows seafloor spreading above the water, which makes it easier to study

Plate Tectonic Theory Theory of Plate Tectonics -Earth’s crust is broken into plates which float and move.

Earth’s crust made of many plates is similar to the panels on the outside of a soccer ball.

There are about 13 plates covering Earth’s surface

Plate Boundaries (edges) When the plates move, their boundaries, or edges, can scrape and collide. http://www.wwnorton.com/college/geo/egeo/flash/2_6.swf

Different Types of Boundaries http://pubs.usgs.gov/gip/dynamic/understanding.html

Convergent Boundary Plates move toward each other

Convergent Boundary When two continental plates move into each other, the plates combine and form mountains. (India into Asia) http://www.classzone.com/books/earth_science/terc/content/visualizations/es1105/es1105page01.cfm?chapter_no=visualization

Convergent Boundary – Indian and Eurasian Plates Indian Plate

Convergent Boundary When an oceanic plate runs into a continental plate, the heavier oceanic plate subducts (sinks) back into the mantle. Volcanic mountains are created along this edge.

Oceanic plate into continental Example: Pacific plate (oceanic) subducts (sinks) under Japan (continental). http://maps.google.com/

Convergent Boundary – Oceanic & Continental http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com

Convergent Boundary – Oceanic & Oceanic Note – plates are reversed http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com

Convergent Boundaries - Continental http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com

Divergent Boundary Plates move apart

When both diverging plates are both oceanic, it is called seafloor spreading (Mid-Atlantic Ridge)

Divergent Boundary - Oceanic http://www.geology.com

When both diverging plates are continental it is called rift valley formation (Africa) http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::640::480::/sites/dl/free/0072402466/30425/19_21.swf::Fig.%2019.21%20-%20Evolution%20of%20a%20Divergent%20Plate%20Boundary

Divergent Boundary - Continental http://www.geology.com

Divergent Boundary – Arabian and African Plates Arabian Plate Red Sea African Plate

Divergent Boundary – Iceland http://pubs.usgs.gov/gip/dynamic/understanding.html

Transform Boundary Plates slide past each other

San Andreas Fault, CA Each time the plates slide past each other, an earthquake occurs

San Andreas Fault

Transform Boundary – San Andreas Fault United States California www.geology.com

Find the three boundaries

Asthenosphere A plastic-like layer found below the lithosphere. The rigid oceanic and continental plates of the lithosphere sit on top

The Asthenosphere is heated by the hot Outer Core

Convection Current crust mantle core Hot material rises, cooler material sinks, creating a current, called a Convection Current

When the asthenosphere moves, it carries the lithospheric plates (divergent, convergent, and transform motions) Convection currents cause plate motion http://www.absorblearning.com/media/attachment.action?quick=12p&att=2775

Every time these plates move we get earthquakes, volcanic eruptions, and possibly tsunamis

Review (These will be quiz questions) Name the 3 main layers of the Earth What is a tectonic plate? What was Pangea? What is Sea-Floor spreading? Name the three different types of plate boundaries and one location on Earth for each one. What causes the plates to move?