Drift

• Continental Drift Theory


  Theory that continents move around on Earth's surface and were once joined together as a single supercontinent
• Continental Drift Theory


  • Developed by Alfred Wegener
  • Describes one of the earliest ways geologists thought continents moved over time
  • Has been replaced by the science of plate tectonics
• Fossils


  • Trace of an ancient organism
  • Fossils of the ancient reptile Mesosaurus found only in southern Africa and South America
  • Fossils of tropical plants found in the Arctic archipelago of Svalbard, Norway
• Mesosaurus, a freshwater reptile only one meter (3.3 feet) long, could not have swum the Atlantic Ocean. The presence of it suggests a single habitat with many lakes and
• The fossils of tropical plants found in Svalbard, Norway suggest that Svalbard once had a much warmer, more humid environment
• Wegener studied the stratigraphy of different rocks and mountain ranges and found that the east coast of South America and the west coast of Africa seem to fit together like pieces of a jigsaw puzzle
• Plate Tectonics


  Scientific theory that explains how major landforms are created as a result of Earth's subsurface movements
• Plate Tectonics


  • The continents rest on massive slabs of rock called tectonic plates
  • The plates are always moving and interacting in a process called
• Seafloor spreading


  
  

  - process where molten rock rises from within the Earth and adds new seafloor (oceanic crust) to the edges of the old

  - as the seafloor grows wider, the continents on opposite sides of the ridge move away from each other
• Plate Tectonics

  • Earth's outermost layer, or lithosphere, is broken into large rocky plates that lie on top of a partially molten layer of rock called the asthenosphere
  • The plates move relative to each other at different rates, from two to 15 centimeters (one to six inches) per year due to the convection of the asthenosphere and lithosphere
• Subduction zone


  A collision between two of Earth's tectonic plates, where one plate sinks into the mantle underneath the other plate
• Most volcanoes are found above subduction zones, but some form far away from these plate boundaries. This question was finally answered in 1963 by a Canadian geologist, John Tuzo Wilson, who proposed that volcanic island chains, like the Hawaiian Islands, are created by fixed "hot spots" in the mantle
• Types of tectonic boundaries

  • Convergent - where plates move into one another
  • Divergent - where plates move apart
  • Transform - where plates move sideways in relation to each other
• Convergent Boundaries


  1. Where plates serving landmasses collide, the crust crumples and buckles into mountain ranges

  2. India and Asia crashed about 55 million years ago, slowly giving rise to the Himalaya, the highest mountain system on Earth
• Divergent Boundaries


  1. At this kind of boundaries in the oceans, magma from deep in the Earth's mantle rises toward the surface and pushes apart two or more plates

  2. On land, giant troughs such as the Great Rift Valley in Africa form where plates are tugged apart
• Transform Boundaries


  1. The San Andreas Fault in California is an example, where two plates grind past each other along what are called strike-slip faults

  2. These boundaries don't produce spectacular features like mountains or oceans, but the halting motion often triggers large earthquakes
• Mid-ocean ridges


  giant underwater mountain ranges
• Lithosphere


  • Earth's outermost layer made of crust and upper mantle and is broken into large rocky particles
• Asthenosphere


  partially molten layer of rock where large rocky plates lie on top of it
• Year 1950 and 1960


  Wegener's theory gained steam as new data began to support the idea of continental drift
• Harry Hess


  American geologist proposed that ridges were the result of molten rock rising from asthenosphere
• year 1963 by John Tuzo Wilson


  he proposed that volcanic island chains are created by fixed hot spots in the mantle