Forces the Shape the Earth

8.6.5 Explain the concepts of continental drift and plate

tectonics.

New Zealand Earthquake

• The earthquake that devastated a city in New Zealand tore open a new 11ft faultine in the Earth’s surface.

• The 7.1-magnitude quake which hit Christchurch, the country’s second-largest city, destroyed about 500 buildings and caused an estimated £930million of damage.

• But hundreds of lives were saved by tough building rules, it was claimed. Only two injuries were reported.

New Zealand Earthquake Seismograph

New Zealand Earthquake

New Zealand Earthquake

• The quake was caused by the continuing collision between the Pacific and Australian tectonic plates, said Professor Mark Quigley, of Canterbury University.

• ‘One side of the Earth has lurched to the right ... up to 11ft and in some places been thrust up,’ he said. ‘We went and saw two houses that were completely snapped in half by the earthquake.’

The Pacific plate is gradually being pushed beneath the Australian plate, which caused Friday's massive

earthquake

New Zealand Earthquake

Earth’s Major Plates

• The map of the Earth is always changing; not only are the underlying plates moving, but the plates change in size. Also, the sea level changes over time (as the temperature on Earth varies and the poles melt or freeze to varied extents), covering or exposing different amounts of crust.

Earth’s Major Plates

• The current continental and oceanic plates include: the Eurasian plate, Australian-Indian plate, Philippine plate, Pacific plate, Juan de Fuca plate, Nazca plate, Cocos plate, North American plate, Caribbean plate, South American plate, African plate, Arabian plate, the Antarctic plate, and the Scotia plate. These plates consist of smaller sub-plates.

1. Earth’s Major Plates

PLATE TECTONICS

• PLATE TECTONICSThe theory of plate tectonics (meaning "plate structure") was developed in the 1960's. This theory explains the movement of the Earth's plates (which has since been documented scientifically) and also explains the cause of earthquakes, volcanoes, oceanic trenches, mountain range formation, and many other geologic phenomenon.

2. Earth’s Crust

TYPES OF PLATE MOVEMENT

• TYPES OF PLATE MOVEMENT: Divergence, Convergence, and Lateral SlippingAt 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.

3. Convergent Boundaries

• The plates move in three different ways. One way they move is together →←. Convergent boundaries are places where two plates come together. When two plates move together, one can expect to find a great deal of volcanoes, earthquakes and mountain building. One can also see subduction zones, places where one plate is slipping below another plate

4. Divergent Boundaries• Another way plates move is apart

↔. Places where the plates move apart are called divergent boundaries. When plates move apart, sometimes land will split apart. For instance, Iceland is located over a divergent boundary and eventually the island will split in half. One can also find rift zones at divergent boundaries. When two plates move apart, it forms a rift, or crack, in the Earth’s crust. From this rift flows molten hot lava from beneath. This can result, over time, in a mountain range. When the molten lava flows from an underwater rift, it produces new seafloor. One well known rift zone is The Mid-Atlantic Ridge, located in the middle of the Atlantic Ocean. In this location, the seafloor is expanding as we speak.

5. Transform Boundaries

• Plates can also grind against one another ↑↓. Places where this occurs are called transform boundaries. When plates rub against one another, they can produce a fault. A fault is a crack in the Earth’s crust. The San Andreas Fault is an exam of a transform boundary.

6. "Hot Spots"

• The exception to this arrangement are "Hot Spots" which are plumes of hot material (rather than belts) in the middle of plates. These spots stay stationary while the plate moves above it. The spot melts through the plate like a blow torch and produces a volcano above it. As the plate moves, the spot melts through another spot producing a chain of volcanic islands. Hawaii is an example of a hot spot island chain.

1. What type of boundary?

2. Types of Plate Boundaries

3. Evidence of Continental Drift

• 1. Puzzle Fit of the continents to form Pangaea• 2. Fossil Evidence• 3. Glacial Evidence (see below) • 4. Coal in Antarctica- coal is formed in tropical

swamps. Coal was formed when Antarctica was closer to the equator.

• 5. Magnetic Stripes on the ocean floor • 6. Mountain Chains appear where they should if

continents are colliding

4. Fossil Evidence

• Fossil Evidence- in the picture above, fossils of many land-living have been found on opposite shores. When Pangaea is re-assembled, the fossils match up.

4. Fossil Evidence

• Glossopteris – A Fern

• Cynognathus – A Land Reptile

• Lystrosaurus – A Land Reptile

• Mesosaurus – A freshwater reptile

5. Glacial Evidence

• when Pangaea is re-assembled, there is evidence of a single ice sheet affecting many of the southern continents. When viewed this way, this sheet leaves consistent evidence of a single glacier. When viewed on the current continents, it is inconsistent and even highly improbable. For example, India, which is north or the Equator, has glacial evidence coming from the south!

5. Glacial Evidence

• Rocks and sediments are added to glaciers through various processes. Glaciers erode the terrain principally through two methods: abrasion and plucking

5. Glacial Evidence• As the glacier flows over the

bedrock's fractured surface, it softens and lifts blocks of rock that are brought into the ice. This process is known as plucking, and it is produced when subglacial water penetrates the fractures and the subsequent freezing expansion separates them from the bedrock. When the ice expands, it acts as a lever that loosens the rock by lifting it. This way, sediments of all sizes become part of the glacier's load. The rocks frozen into the bottom of the ice then act like grit in sandpaper.

The Baltoro Glacier in the Karakoram Mountains, Pakistan

The ice calving end of the Perito Moreno Glacier, in the western

Patagonia of Argentina

Icebergs breaking off glaciers at Cape York, Greenland

Magnetic Stripes on the ocean floor

• When the molten rock hardens, the magnetic minerals in the rock align themselves with the Earth's magnetic field. Scientists discovered that the Earth's magnetic field has reversed itself many times, at intervals of roughly every 100,000 years. The pattern they observed makes sense if the ocean floor is being formed at the ridge and gradually pushed outward in both directions

6. Mountain Chains

• 6. Mountain Chains appear where they should if continents are colliding