Birth of an islandBirth of an island

海洋科學：地質面向海洋科學：地質面向

The Earth in cross sectionThe Earth in cross section

The chemical and The chemical and physical physical organization of the organization of the Earth’s Layers Earth’s Layers comparedcompared

The layering of tThe layering of the lithosphere ahe lithosphere and asthenosphernd asthenosphere in more detaile in more detail

Characteristics of the Earth’s LayersCharacteristics of the Earth’s Layers

大陸飄移假說大陸飄移假說（（ Continental Drifting HypothesisContinental Drifting Hypothesis ）→）→海底擴展學說（海底擴展學說（ Seafloor SpreadingSeafloor Spreading ）→）→板塊構造學說（板塊構造學說（ Plate TechtonicsPlate Techtonics ））

Seismic events worldwide, Seismic events worldwide, January 1977 through December 1986January 1977 through December 1986

The fit of all the The fit of all the continents around continents around the Atlanticthe Atlantic

Reconstruction of PangaeaReconstruction of Pangaea

The major lithosphere platesThe major lithosphere plates

板塊構造學說（ Plate Techtonics）

An overview of the plate tectonics processAn overview of the plate tectonics process

The formation of The formation of a new plate a new plate boundary:boundary:the breakup of the breakup of PangaeaPangaea

The South Atlantic in cross section, showing the The South Atlantic in cross section, showing the mid-ocean ridge at a divergent plate boundarymid-ocean ridge at a divergent plate boundary

A cross section A cross section through the west coast through the west coast of South Americaof South America

The formation of an island arc along a The formation of an island arc along a trench as two oceanic plates convergetrench as two oceanic plates converge

The convergence of two continental platesThe convergence of two continental plates

Characteristics of the Plate BoundariesCharacteristics of the Plate Boundaries

A long transform A long transform plate boundaryplate boundary

Key Concepts for Plate Tectonics (I)Key Concepts for Plate Tectonics (I)

• Earth is composed of concentric spherical layers, with the least Earth is composed of concentric spherical layers, with the least dense layer on the outside and the densest as the core.dense layer on the outside and the densest as the core.

• The lithosphere, the outmost solid shell that includes the crust,The lithosphere, the outmost solid shell that includes the crust, floats on the hot, deformable asthenosphere. The mantle is thefloats on the hot, deformable asthenosphere. The mantle is the largest of the layers.largest of the layers.

• Large regions of Earth’s continents are held above sea level byLarge regions of Earth’s continents are held above sea level by isostatic equilibrium, a process analogous to a ship floatingisostatic equilibrium, a process analogous to a ship floating in water.in water.

• Some seismic waves – energy associated with earthquakes – canSome seismic waves – energy associated with earthquakes – can pass through the Earth. Analysis of how these waves are changed,pass through the Earth. Analysis of how these waves are changed, and the time required for their passage, has told researchers muchand the time required for their passage, has told researchers much about conditions inside Earth. about conditions inside Earth.

Key Concepts for Plate Tectonics (II)Key Concepts for Plate Tectonics (II)

• Plate tectonics theory suggests that Earth’s surface isPlate tectonics theory suggests that Earth’s surface is not a static arrangement of continents and ocean, but anot a static arrangement of continents and ocean, but a dynamic mosaic of jostling segments of lithospheredynamic mosaic of jostling segments of lithosphere called lithospheric plates. The plates have collided,called lithospheric plates. The plates have collided, moved apart, and slipped past one another sincemoved apart, and slipped past one another since Earth’s crust first solidified.Earth’s crust first solidified.

• Plate motion is driven by slow, heat-generatedPlate motion is driven by slow, heat-generated (convection) currents flowing in the mantle. Most of the(convection) currents flowing in the mantle. Most of the heat is generated by the decay of radioactive elementsheat is generated by the decay of radioactive elements within Earth.within Earth.

Key Concepts for Plate Tectonics (III)Key Concepts for Plate Tectonics (III)

• Most of the large-scale features seen at Earth surfaceMost of the large-scale features seen at Earth surface may be explained by the interactions of plate tectonics.may be explained by the interactions of plate tectonics. Plate tectonics also explains why our ancient planet hasPlate tectonics also explains why our ancient planet has surprisingly young seafloors, the oldest of which is onlysurprisingly young seafloors, the oldest of which is only as old as the dinosaurs, that is, about 1/23 the age ofas old as the dinosaurs, that is, about 1/23 the age of Earth.Earth.

• The confirmation of plate tectonics rests on diverseThe confirmation of plate tectonics rests on diverse scientific studies from many disciplines. Among thescientific studies from many disciplines. Among the most convincing is the study paleomagnetism, themost convincing is the study paleomagnetism, the orientation of Earth’s magnetic field frozen into rocksorientation of Earth’s magnetic field frozen into rocks as it solidified.as it solidified.

The End The End Thank you for your attention Thank you for your attention

(if you have been staying awake)(if you have been staying awake)