Plate Tectonics

What is it and why do we need to know?

Some questions we will answer...

·How is the earth always changing?·What forces inside the earth create and change landforms on the surface?·What is the theory of plate tectonics and how does it work?·What two theories help make up the theory of plate tectonics?·What is continental drift and sea floor spreading?·What happens when the plates crash together, pull apart, and slide against each other?

Key Terms: Knowledge SurveyPlate Tectonic Prior Knowledge Survey1 = Haven’t a Clue2 = Know I have heard it, but I can’t define it.3 = Know I have heard it, have some sense of its meaning4 = Have a good sense of the meaning when I see it or hear it5 = Can define it and explain its meaning to someone else

crust - the rigid, rocky outer surface of the Earth, composed mostly of basalt and granite. The crust is thinner under the oceans. mantle - a rocky layer located under the crust - it is composed of silicon, oxygen, magnesium, iron, aluminum, and calcium. Convection (heat) currents carry heat from the hot inner mantle to the cooler outer mantle. outer core - the molten iron-nickel layer that surrounds the inner core. inner core - the solid iron-nickel center of the Earth that is very hot and under great pressure.

Crust

Mantle

Outer Core

Inner Core

Layers of the earth Boundaries.asf

The Earth’s LayersThe Earth is made of many different and distinct layers. The deeper layers are composed of heavier materials; they are hotter, denser and under much greater pressure than the outer layers.

Natural forces interact with and affect the earth’s crust, creating the landforms, or natural features, found on the surface of the earth.

Lithosphere

The lithosphere (geosphere) is the "solid" part of Earth. It has two parts, the crust and the upper mantle.

Asthenosphere  A zone of the earth's mantle that lies beneath

the lithosphere and consists of several hundred kilometers of gooey, candy like rock.

Land and WaterPhotographs of the earth taken from space show clearly that it is a truly a ”watery planet.”More than 70 percent of the earth’s surface is covered by water, mainly the salt water of oceans and seas.

What are the planets main oceans? List them in your notes. Hint: there are 6!

mantle convection

Heat transfer from the core to the mantle produces slow convection

of the mantle material this is what fuels plate movement

(in the order of centimetres per year)

Mantle convection produces the energy for movement at the boundary between the mantle and the crust

The Theory of Plate TectonicsBasic Plate Tectonics Concepts

1. The outer portion of the Earth, the lithosphere (the upper mantle and crust), is composed of rigid units called plates.

2. Plates move slowly.

3. Most of the Earth’s large-scale geologic activity, such as earthquakes and volcanic eruptions, occur at or near plate boundaries.

4. Interiors of plates are geologically quiet, with fewer and usually milder earthquakes and fewer volcanoes than at plate boundaries.

The Earth's surface is broken into ~15 crustal plates

The Theory of Plate Tectonics

When plates move, everything on them moves with them.North American Plate moving west, Eurasian Plate moving east.Rate is about 5-10 cm/yr.Over long periods of time, movement is large.

The Theory of Plate TectonicsSo….

Has the size of the Earth increased?

Why?

Where plates move apart or diverge, at some other place on the Earth, they must come together orconverge.

This is where the Earth gets exciting.

Divergent- The plates are moving apart

This is an example of a divergent plate boundary (where the plates move away from each other) The Atlantic Ocean was created by this process. The mid-Atlantic Ridge is an area where new sea floor is being created. As the rift valley expands two continental plates have been constructed from the original one. The molten rock continues to push the crust apart creating new crust as it does. As the rift valley expands, water collects forming a sea.

Convergent Boundaries Plates are destroyed!

This is a convergent plate boundary, the plates move towards each other. The amount of crust on the surface of the earth remains relatively constant. Therefore, when plates diverge (separate) and form new crust in one area, the plates must converge (come together) in another area and be destroyed. An example of this is the Nazca plate being subducted under the South American plate to form the Andes Mountain Chain.

Types of convergent boundaries:

·Oceanic-Oceanic-Islands are created.

Oceanic-Oceanic

Mt. Fuji in Japan

Mt. Fuji in Japan

Oceanic- Continental

Continental-Continental

Mt. Everest

Continental-Continental

Transform plate boundaries At transform plate boundaries plates grind past each other side by side. This type of boundary separates the North American plate from the Pacific plate along the San Andreas fault, a famous transform plate boundary that’s responsible for many of California’s earthquakes.