Continental Drift and Plate Tectonics Earthquakes, volcanoes, and mountains have a shared origin and serve to remind us that our planet is constantly changing. During this interactive unit you will explore Alfred Wegener’s continental drift and plate tectonics theories.

 Topics covered include  Pangaea  Boundaries  mid-ocean ridges  Seafloor spreading  Subduction zones  Faults and seismic waves.

Questions you will be able to answer following this lesson: 1. What evidence did Alfred Wegener offer to support his theory of continental drift? 2. How does the movement of tectonic plates occur? 3. What are the three types of tectonic plate movement? 4. What changes in the surface of the earth might each of these cause?

Objectives: Students will…  Understand the theory of continental drift.  Explore the processes by which continental drift occurs.  Examine the types of tectonic plate movement and plate boundaries.  Establish a connection between plate movement and geologic events.

Part 1 – Continents Adrift In 1910, Alfred Wegener, a German scientist, hypothesized that all of the continents had once been joined together in a single landmass and have since slowly drifted apart. He named this supercontinent Pangaea, which means “all lands”. This idea of the continents moving become known as continental drift.

Pangaea

Most scientists rejected Wegener’s theory because he could not identify a force that could move the continents. We now know today that this movement of the plates was caused by convection currents in the mantle of our Earth.

The arrows represent the convection currents in the Earth’s mantle.

Part 2 - Sea-Floor Spreading Sea-floor spreading is the process in which the ocean floor is extended when two plates move apart. As the plates move apart, the rocks break and form a crack between the plates. plates

 Earthquakes occur along the plate boundary. Magma rises through the cracks and seeps out onto the ocean floor like a long, thin, undersea volcanoMagma volcano

Example of Sea-Floor Spreading

 As magma meets the water, it cools and solidifies, adding to the edges of the sideways-moving plates. As magma piles up along the crack, a long chain of mountains forms gradually on the ocean floor. This chain is called an oceanic ridge. magma platesmagma

 The boundaries where the plates move apart are 'constructive' because new crust is being formed and added to the ocean floor. The ocean floor gradually extends and thus the size of these plates increases. As these plates get bigger, others become smaller as they melt back into the Earth in the process called subduction.plates subduction

 An example of an oceanic ridge in nature is the Mid-Atlantic Ridge. It is one part of a system of mid-oceanic ridges that stretches for 50,000 miles through the world's oceans.  Sea-floor spreading is basically volcanic, but it is a slow and regular process, without the explosive outbursts of the volcanoes on land.volcanoes Volcano Brain Pop

Mid-Atlantic Ridge

Part 3 – The Theory of Plate Tectonics In 1965, a Canadian scientist, J. Tuzo Wilson, observed that there were cracks in the continents similar to those on the ocean floor. He proposed that the lithosphere was broken into separate sections called plates.

Wilson combined what geologists know about sea-floor spreading, Earth’s plates, and continental drift into a single theory which became known as the theory of plate tectonics.

Plate Tectonics  Plate tectonics is the geological theory that states that pieces of Earth’s lithosphere are in constant, slow motion, driven by convection currents in the mantle.

The theory of plate tectonics explains the formation, movement, and subduction of Earth’s plates.  There are a total number of 52 tectonic plates in the world today: 14 major tectonic plates and 38 minor tectonic plates.

Plate Boundaries The different pieces of the lithosphere meet at lines called plate boundaries. Faults, which are breaks in Earth’s crust where rocks have slipped past each other, form along these boundaries.

There are three types of plate boundaries found in the Earth’s lithospshere: 1. Transform boundaries 2. Divergent boundaries 3. Convergent boundaries

Transform Boundaries At a transform boundary, two plates move along the boundary in opposite directions. The San Andreas Fault is an example of a transform boundary. The Pacific plate is sliding past the North American plate.

San Andreas Fault

Divergent Boundaries The place where two plates move apart or divide is called a divergent boundary. Most divergent boundaries occur at the mid-ocean ridge.

When a divergent boundary develops on land, two of Earth’s plates pull apart and creates a rift valley. The Rio Grande rift is a divergent boundary on land that extends from central Colorado to El Paso, Texas.

Rio Grande Rift

Convergent Boundaries  The place where two plates come together is called convergent boundary. When two plates converge, the result is called a collision.  The Appalachian Mountains and the Himalayas formed as a result of a convergent boundary in which two continental plates collided. Plate Tectonics Brain Pop

Appalachian Mountains

Part 4 – Earth’s Crust in Motion Stresses on Earth’s crust produce compression, tension, and shearing in rock. Sometimes faults occur which are cracks in Earth’s crust from the result of stress. (San Andreas Fault) Faulting and folding of the Earth’s crust cause mountains and other features to form on the surface.

Earth’s Crust in Motion  An earthquake is the shaking and trembling that results from the movement of rock beneath Earth’s surface. The movement of Earth’s plates creates powerful forces that squeeze or pull the rock in the crust. These forces are examples of stress, a force that acts on rock to change its shape or volume.  Earthquake BrainPop Earthquake BrainPop

1964 Earthquake in Alaska

Tsunamis  A tsunami is a giant water wave that is formed when an earthquake jolts the ocean floor and causes plate movement.

2004 Tsunami that hit the south Asian shoreline

Earthquakes in New Jersey?

Earthquakes in New Jersey Yes, believe it or not, New Jersey has had earth quakes. Check out the following websites and explore this topic