PLATE TECTONICSPLATE TECTONICSTo BuildTo Build

2:5A2:5A

2:5 A cont.2:5 A cont.

• The continental crust averages 35 km. deep – both are relatively thin.

• The crust covers a thick, molten, moving mantle (68% of Earth’s volume) and a heavy core, possibly composed of nickel and iron.

• The plates are moving in different directions further cracking the crust

Earth’s Lithospheric PlatesEarth’s Lithospheric Plates

• Is divided into large and small crustal plates

• Makes up the ocean floor AND the continental land masses, along with the upper mantle.

• The ocean crust averages 8 km. deep but is dense enough to support the continental crust riding on it.

By looking at seismic activity By looking at seismic activity around the world, scientist can around the world, scientist can identify the plate boundaries.identify the plate boundaries.

These are the major plates: North These are the major plates: North American, S. American, Pacific, Eurasian, American, S. American, Pacific, Eurasian, African, Nazca, Indo-Australian, and the African, Nazca, Indo-Australian, and the

Antarctic plate.Antarctic plate.

2:5 C 3 Types of Plate Boundaries2:5 C 3 Types of Plate Boundaries

• 1. OCEANIC to OCEANIC

divergent – meaning to move aparta. Both plates are composed of basalt – the primary type

of ocean floor rock, also iron, magnesium, and silicon

b. Both plates have the same high density rock

c. The result is a vent. Ex. Mid-Ocean ridge (MOR)

This same ridge is 40,000 miles long and is found in many places other than the middle of the Atlantic Ocean

Cont. 2:5 CCont. 2:5 C

• 2. Continental to Continental boundary – convergent, meaning to come togethera. Both plates are granite – a type of igneous rock that is the basis of the rock cycle; also silicon and aluminum

b. Plates have the same low density rock

c. The result is that the edges are forced up into mountains. Ex. Himalayas, Atlas Mts

Cont. 2.5 CCont. 2.5 C

• 3 Oceanic to Continental boundary – a subduction zone where plate edges over ride or slide past each other.a. Lighter continental plate edges override the denser oceanic plate

b. Oceanic plate edges are subducted down into the asthenosphere and are remelted

c. The result is trenches ex. Peru/Chile Trench

2:6 A The Pangea Theory2:6 A The Pangea Theory

• 1912 Alfred Wegener proposed the idea that the continents were once part of a huge land mass, called Pangea (all lands), that later broke up.

He was convinced because:1. the continents shape roughly fit together like a puzzle

2. the rocks and fossils on different continents matched

Cont. Cont.

• His theory of Continental Drift was ignored because of thin data. As a German meteorologist, he lack credentials, and he couldn’t explain how huge continents moved.

• In the early 60’s, Harry Hess and J. Wilson, proposed a mechanism for continental movement, but they called it “geo-poetry” to avoid criticism

1996 The 1996 The Glomar ChallengerGlomar Challenger drilled a drilled a series of holes in the MOR -. What they series of holes in the MOR -. What they

found revolutionized oceanography.found revolutionized oceanography.

2:6 B2:6 B

• Continental rocks date the Earth at about 5 billion years old. Since the ocean floor is lower in the lithosphere, scientists expected to find older rocks at those depths

• Continental geology’s Law of Superposition state that oldest rocks are laid down first and should be found horizontally lowest in the bed unless uplifted.

Cont. 2:6 BCont. 2:6 B

• Instead, they found no rock older than 3 billion years old and most were younger. How can the ocean floor be younger that the continents riding on it?

• The Deep Sea Drilling Project showed that rocks became older as the moved away from the MOR.

Cont. 2: BCont. 2: B

• Oceanic geology showed rock layers created vertically – not according to the Law of Superposition

2:6 C2:6 C• The MOR seemed to be parallel distance from

continents on either side.• Core sampling revealed matching magnetic

striping in the rocks on both sides of the MOR• In 1977 Project FAMOUS using Alvin

photographed magma squeezing out of the MOR and creating new ocean floor.

• Scientist Vine and Matthews now had the data for a cohesive theory on plate tectonics.

• The sea floor was spreading – moving the continent with it. The theory of sea floor spreading explained continental drift. Wegener was right!

2:7 A Bathymetry of the 2:7 A Bathymetry of the Ocean FloorOcean Floor

• Structures on the ocean floor are mapped by SONAR – sound navigation and ranging (echo sounding)

Depth = time X 1460 meters/sec (speed of sound in water)

2 (round trip)

2: 7 A cont.2: 7 A cont.

• 1. MARGIN:a. Continental shelf – underwater

extension of the continent, most biologically productive area because of light availability.

b. Continental slope – steep cliff to basin, 1-2 mile drop-off where materials tumbled down the slope forming turbidity currents which cut canyons.

c. Continental rise – apron of sediments covering the joint between ocean floor and the continental rocks

2:7 B Basins2:7 B Basins

– A. Abyssal plains – flat featureless region similar to a desert; common in Atlantic and Indian Ocean.

– B. Abyssal hill – dome of sediment that shift like dunes.

– C. Seamount – peaks of volcanic materials– D. Guyot – seamounts truncated by eroision,

like plateaus

2: 7 B cont.2: 7 B cont.

• E. island – seamounts extending out of the water. They differ from continents because they have no margins. Volcanic eruptions create and destroy the terrain. Hot spots under moving plates cause island arcs such as the Hawaiian Island chain. Parts of the chain are still submerged.

2:7 B cont.2:7 B cont.

• Hawaii’s volcano, Mauna Kea, is the highest mountain on Earth. It is 31,000 ft. from the Pacific floor – although only 13,823 feet of it are above water.

• F. Trenches – subduction zones where basalt is being recycled into the mantle or translational zones called faults. Trenches form a boundary around the Pacific; called the “Ring of Fire” because of seismic activity

2:7 C2:7 C

• Mt. Everest, at 29,000 ft could fit into the Mariana trench and still be 7,000 ft. below sea level.

• G. MOR – 40,000 mile long mountain range where new ocean floor is being formed. Divergent plate boundaries are found in all parts of the ocean – not just in the middle of the Atlantic

2:7 C cont.2:7 C cont.

• Iceland is a large section of the MOR extending above the surface

• H. Rift valley – vent resulting from the divergent plate boundaries that allow magma to recreate new ocean floor.

• Ocean bathymetry is very similar to continental topography except that features are smaller due to erosion.

2:8 A Titanic Disaster2:8 A Titanic Disaster

• The R. M. S. Titanic was found in 1985 by Dr. Robert Ballard at Woods Hole Oceanographic Institute using a camera sled and Jason. Jason is a robotic camera commanded from the submersible, Alvin.

• The Titanic rests in the Labrador Sea at a depth of 2 miles. It was found upright, broken into two pieces, facing opposite direction.

2:8 A cont.2:8 A cont.

• The disaster resulted in safety procedures still used by ships at sea.

• The International Convention of Safety of Life at Sea 1913 requires:

• -life boat drills, often at 2:20 . Sunday to commemorate the Titanic.

• -life boat space for all aboard• -24 communication• -International Ice Patrol warns of icebergs twice

daily in the n. Atlantic

2: 8 B2: 8 B

• The royal mail ship, Titanic, was the largest ship ever built at the time. The floating palace cost $7.5 million to construct.

• Built in Belfast, Ireland, Titanic was 882 ft. long; 92 ft wide. Titanic had 16 presumably watertight compartments that divided its double-bottomed hull

Cont.Cont.

• The maiden voyage began on April 10, 1912 from Southhampton, England to New York. The ship’s captain was to retire at the end of a 34 year career when she docked.

• There were 2, 227 passengers and crew abroad. At 11:40 the night on April 14, the ship struck an iceberg.

Cont.Cont.

• By 2:20 A M on the morning of April 15, she sank with 1,522 passengers and crew members. The 705 survivors were rescued with 1 and a half hours by the Carpathia.

• Famous peple who lost their lives were British journalist, William Thomas Stead, Mr. and Mrs. Isador Strauss, John Jacob Astor, and Major Archibald Butts