Seafloor Spreading and Plate Tectonic Theory PDF

John Aldrich G. Cortez, RN  Due to convection currents in the Earth’s interior, tectonic plates are in constant motion. How do convection currents in the Earth’s interior make the seafloor spread?  New seafloor is formed along mid-oceanic ridges. The need to study the seafloor for...

John Aldrich G. Cortez, RN  Due to convection currents in the Earth’s interior, tectonic plates are in constant motion. How do convection currents in the Earth’s interior make the seafloor spread?  New seafloor is formed along mid-oceanic ridges. The need to study the seafloor for military purposes during World War II led to the development of advanced technologies that allowed detailed studies of the seafloor. These newly acquired data were significantly consistent with Wegener’s continental drift theory.  Harry Hammond Hess – explained how the convection currents in the Earth’s interior make the seafloor spread. Convection currents carry heat from the molten materials in the mantle and core towards the lithosphere.  These currents ensure that the materials formed in the lithosphere are recycled back into the mantle. In this recycling process, which was later named as seafloor spreading, the molten materials flow out to form mid-oceanic ridges, spread sideways to form seafloor, and disappear into the ocean trenches.  The oldest ocean floor rocks ever found are 180 million years old. Remember the Earth is 4.6 billion years old. The rocks closest to the ocean ridge were younger than the rocks found further from the ridge. This means that new rocks are formed at the ridges and push the older rocks away from the ridge.  Plate Tectonic Theory – proposes that the lithosphere consists of seven large and numerous smaller segments called plates. Plates move relative to each other due to convection flow. Plate Boundary – a fracture separating one plate from another.  Types of Plate Boundaries Convergent Boundary – the plates move or collide to each other. 1. Oceanic – Continental Convergence – forms trenches, destructive earthquakes and rapid uplift of mountain ranges as well as volcanic arc. 2. Oceanic – Oceanic Convergence – also forms trenches and volcanic arc. 3. Continental – continental Convergence – forms mountain range like the Himalayan range.  Trenches – are formed at subduction zones where plates collide with each other or at convergent boundaries Divergent Boundary – the plates move away from each other.  Oceanic ridges – are formed at divergent boundaries, where plates move away from each other. Transform Boundary – when plates slide past each other.  Since the pressure and temperature are low at the Earth’s surface, rocks tend to break or fracture when subjected to compressional and tensional stresses. This means that the pressure exerted in the blocks of rocks exceeds the rock's internal strength.  Fractures can either be a fault or a joint. A fault is a break in the rock where there is considerable movement on the fracture surface while a joint is a break where there is no considerable movement.  The theory of plate tectonics provided the explanation for how plates move around through geologic time. J. Tuzo Wilson – the first who formally applied plate tectonics to explain geologic records.  Due to plate tectonics, there is a cyclic rifting in continents that formed ocean basin and subduction that resulted to the destruction or closure of the older basins.  Continental Shelf – a relatively shallow gently sloping part of the continental crust that borders the continent. Its average depth is 130m with a maximum width of about 1300km.  Continental Slope – leads to deep water, quite deep. It represents the true edge of the continent and extends downward to a depth of 4km.  Continental Break – the boundary between the continental slope and shelf. Continental Rise – more gradual incline, that links the deep ocean basin floor to the continental slope.  Ocean Floor – formed at the base of the continental rise. It is 4000m to 6000m deep and accounts for nearly 30% of Earth’s surface.  Element of an Active and Growing Ocean Basin 1. Active and elevated mid – ocean ridge, sloping towards lanking abyssal hills and plains  Atlantic Ocean and Arctic Ocean are examples of active, growing ocean basins. Mediterranean Sea, shrinking sea. Pacific Ocean, active and shrinking ocean basin. Gulf of Mexico and Aleutian Basin, inactive ocean basin.  “You can’t go back to how things were. How you thought they were. All you really have is…now.” -Hannah Baker