Birth of an island 海洋科學：地質面向

The Earth in cross section

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

The layering of the lithosphere and asthenosphere in more detail

Characteristics of the Earth’s Layers

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

Seismic events worldwide, January 1977 through December 1986

The fit of all the continents around the Atlantic

Reconstruction of Pangaea

The major lithosphere plates

板塊構造學說 （ Plate Techtonics ）

An overview of the plate tectonics process

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

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

A cross section through the west coast of South America

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

The convergence of two continental plates

Characteristics of the Plate Boundaries

A long transform plate boundary

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 the floats 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 by Large regions of Earth’s continents are held above sea level by isostatic equilibrium, a process analogous to a ship floating isostatic equilibrium, a process analogous to a ship floating in water. in water. Some seismic waves – energy associated with earthquakes – can Some 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 much and the time required for their passage, has told researchers much about conditions inside Earth. about conditions inside Earth.

Key Concepts for Plate Tectonics (II) Plate tectonics theory suggests that Earth’s surface is Plate tectonics theory suggests that Earth’s surface is not a static arrangement of continents and ocean, but a not a static arrangement of continents and ocean, but a dynamic mosaic of jostling segments of lithosphere dynamic 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 since moved apart, and slipped past one another since Earth’s crust first solidified. Earth’s crust first solidified. Plate motion is driven by slow, heat-generated Plate 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 elements heat is generated by the decay of radioactive elements within Earth. within Earth.

Key Concepts for Plate Tectonics (III) Most of the large-scale features seen at Earth surface Most 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 has Plate tectonics also explains why our ancient planet has surprisingly young seafloors, the oldest of which is only surprisingly young seafloors, the oldest of which is only as old as the dinosaurs, that is, about 1/23 the age of as old as the dinosaurs, that is, about 1/23 the age of Earth. Earth. The confirmation of plate tectonics rests on diverse The confirmation of plate tectonics rests on diverse scientific studies from many disciplines. Among the scientific studies from many disciplines. Among the most convincing is the study paleomagnetism, the most convincing is the study paleomagnetism, the orientation of Earth’s magnetic field frozen into rocks orientation of Earth’s magnetic field frozen into rocks as it solidified. as it solidified.

The End Thank you for your attention (if you have been staying awake)