Earth science. Plate Tectonics ppt

Four Systems

of

Our

Earth

Plate TectonicsPlate Tectonics

The Geosphere – solid Earth The geosphere is in a constant state of

motion that gives rise to movement of the continents.

The unifying theory that explains how continental drift is possible is called plate tectonics, which was developed by geologists in the 1960s.

Earth has 4 layers

Earth has four layers Outermost layer is the crust. Solid layer that flows slowly like putty is the

mantle. Outer core— molten metal above the inner core. Inner core— dense iron core; very hot and dense.

Why/ How is the geosphere in constant motion?

Plate boundaries are edges where plates meet.

The Earth’s Interior

The Science of GeologyThe Science of Geology

Geologists – scientists Geologists – scientists who study the forces that who study the forces that make and shape planet make and shape planet EarthEarth

Landforms – features Landforms – features formed in rock and soil by formed in rock and soil by water, wind and waveswater, wind and waves

Geology – the study of planet Earth

Studying surface changes

1. Constructive forces – shape the surface by building up mountains and landmasses.

Ex: land is made Destructive forces – slowly wear

away mountains and other land features.

Ex: land is destroyed

A Journey to the Center of the Earth –

Temperature – at a depth of about 20m the temperature gets warmer as you go deeper into the earth’s interior. For every 40 m, the temperature rises 1degree C, then it eventually increases more slowly.

Pressure – the deeper you go the greater the pressure (force pushing on a surface of area)

The Crust – layer of rock that forms the Earth’s outer skin. Includes soil, water, mountains, etc. It is the thinnest layer – thinner beneath the oceans than beneath the continents (5 – 40 km thick)

Oceanic Crust – the crust beneath the oceans. Consists mostly of basalt rock.

Continental crust – the crust beneath the continents. Consists mostly of granite rock.

Evidence for Continental Drift

Alfred Wegener (1880-1930), a German scientist was the first person to propose the theory of continental drift.

200 mya the continents were originally joined together, forming Pangaea, meaning "All-earth".

Continental Drift

– theory that the continents had once been joined together in a single landmass and have since drifted apart.

Theory first proposed by Alfred Wegener Pangaea – the one supercontinent believed to

have existed 300 million years ago

Drifting Continents

Chapter 9, Section 3

Pages 326 – 330

Evidence for Continental Drift

Evidence from landforms Mountain range – in Africa

matched a mountain range in South America

European coal fields match coal fields in North America

Evidence for Continental DriftEvidence from Fossils

Fossil – trace of an organism that has been preserved in rock

Mesosaurus – reptile whose fossils were found in S. America and Africa. This organism could not have swum long distances in salt water,

Evidence for Continental Drift

Evidence from fossils (continued)Lystrosaurus – reptile whose fossils were

found in Africa and India. This organism could not have swum across the ocean.

Glossopteris – a seed fern plant. Identical fossils were found in S. America, Africa, Antarctica, India and Australia. /seeds could not have traveled by air or water across vast oceans.

Evidence for Continental Drift

Evidence from climate Spitsbergen island – located in

the Arctic Ocean, north of Norway. Fossils of tropical plants have been found there.

Evidence that continental glaciers once covered S. Africa

Scientists Reject

Hypothesis

Wegener could not provide a satisfactory explanation for the force that pushes or pulls continents

geologists rejected the theory (until new evidence was discovered later.)

The answer to “WHY”

We know today that the reason plates do move as in the theory of continental drift is due to convection currents.

Convection Currents and the Mantle

Methods of Heat Transfer

Convection – heat transfer by currents moving through a heated fluid (liquid or gas).

Ex: Warm air rises and cool air sinks in a room.

http://www.solarviews.com/eng/edu/convect.htm

Convection in the Earth’s Mantle The (lower mantle) is heated by the outer core,

the heated rocks become less dense and rise, while the cooler rocks from above sink. The repeated process results in continuous cycles of material.

Sea-Floor Spreading

The Theory of Sea-Floor Spreading

Harry Hess in 1960 The ocean floors move like conveyer

belts, carrying the continents with them. Since the continents are attached to the

ocean floor, sea-floor spreading could be the force causing the continents to move.

The theory of sea floor spreading

At mid-ocean ridges molten material rises from the mantle and erupts.

The molten material then spreads out, pushing older rock to both sides of the ridge.

Evidence from Molten Material – scientists discovered “pillow lava” forming along the mid-ocean ridge. These rocks form when molten material hardens quickly after erupting under water.

Evidence from Magnetic Stripes – patterns of magnetic stripes match on either side of the mid-ocean ridge, suggesting that the ocean floor is spreading evenly in opposite directions.

Evidence (continued) Evidence From Drilling Samples – The

Glomar Challenger, a drilling ship, drilled holes in the ocean floor. Discovered that rocks along mid-ocean ridges are much younger than rocks farther away.

Subduction at Deep—Ocean Trenches

Subduction – process whereby the ocean floor plunges into the mantle and melts at deep underwater canyons called deep-ocean trenches.

Subduction at Deep—Ocean Trenches

Subduction and Sea-Floor Spreading work together like a conveyor belt, moving the continents.

Subduction at Deep—Ocean Trenches (cont.)

Subduction and the Earth’s Oceans Subduction in the Pacific Ocean – the deep

trenches surrounding the Pacific Ocean result in more subduction that sea-floor spreading. The result is that the Pacific Ocean floor is getting smaller.

Subduction in the Atlantic Ocean – the Atlantic

Ocean floor is becoming

TYPES OF PLATE MOVEMENT

Divergence, Convergence, and Transform At the boundaries of the plates, various

deformations occur as the plates interact; they separate from one another (seafloor

spreading), collide (forming mountain ranges), slip past one another (subduction zones, in which

plates undergo destruction and remelting), and slip laterally.

Divergent Plate Movement Seafloor spreading is the

movement of two oceanic plates away from each other. This results in the formation of new oceanic crust (from magma that comes from within the Earth's mantle)

Happens along a a mid-ocean ridge.

Where the oceanic plates are moving away from each other is called a divergence boundary.

Convergent Plate Movement: When two plates collide, some

crust is destroyed in the impact and the plates become smaller. The results differ, depending upon what types of plates are involved.    Oceanic Plate and Continental Plate - When a thin, dense oceanic plate collides with a relatively light, thick continental plate, the oceanic plate is forced under the continental plate; this phenomenon is called subduction.    Two Oceanic Plates - When two oceanic plates collide, one may be pushed under the other and magma from the mantle rises, forming volcanoes in the vicinity. Two Continental Plates - When two continental plates collide, mountain ranges are created as the colliding crust is compressed and pushed upwards.

Lateral Slipping Plate Movement When two plates move

sideways against each other, there is a tremendous amount of friction which makes the movement jerky.

The plates slip, then stick as the friction and pressure build up to incredible levels.

When the pressure is released suddenly, and the plates suddenly jerk apart, this is an earthquake.

www.bloust.com/henley