Earth Science

• Weathering


  The breakdown of rocks and minerals into smaller particles
• Insolation weathering or thermal stress weathering

  • Rocky desert landscapes are particularly vulnerable
  • The outer layer of desert rocks undergoes repeated stress as the temperature changes from day to night
  • Eventually, outer layers flake off in thin sheets, a process called exfoliation
• Bornhardts


  • Tall, domed, isolated rocks often found in tropical areas
  • Sugarloaf Mountain, an iconic landmark in Rio de Janeiro, Brazil, is a bornhardt
• Frost Weathering/Cryofacturing


  1. Ice works as a wedge, slowly widening the cracks and splitting the rock

  2. When ice melts, liquid water performs the act of erosion by carrying away the tiny rock fragments lost in the split

  
• Unloading or pressure release

  1. Occurs when the overlying rock is eroded away, causing the outer rock layer to expand more than the layers underneath

  2. The overlying rock material exerts tremendous pressure on the igneous rock

  3. As the rock surface expands, it becomes vulnerable to fracturing in a process called sheeting

  
• Haloclasty


  Salt also works to weather rock, as saltwater sometimes gets into the cracks and pores of rock, and if the saltwater evaporates, salt crystals are left behind, putting pressure on the rock and slowly breaking it apart

  
• Honeycomb weathering


  • Rock formations with hundreds or even thousands of pits formed by the growth of salt crystals, common in coastal areas where sea sprays constantly force rocks to interact with salts
• Factors that may affect metamorphism

  • Pressure
  • Stress
  • Temperature
  • Parent rock
  • Time
  • Fluid
• 90% of Earth's heat is from radioactive decay within the core, and 10% is from the process of accretion that happened 4.6 billion years ago
• Compression Stress


  • Causes the rocks to push or squeeze against one another, can cause either horizontal or vertical orientation, can push rocks together or cause the edges of each plate colliding to rise, mountains are a result of high-impact compression stress
• Tension Stress


  • The opposite of compression, forces the rocks to pull apart, can happen as two separate plates move farther away from each other or the ends of one plate can move in different directions
• Shear Stress


  • When the force of the stress pushes some of the crust in different directions, can cause a large part of the crust to break off, the friction can cause earthquakes
• Confining Stress


  • When stress is applied to all sides of the crust, causes the crust to compact and can fracture from the inside, can cause sinkholes

  
• Elastic deformation


  The rock returns to its original shape when the stress is removed
• Plastic deformation


  The rock does not return to its original shape when the stress is removed
• Fracture


  The rock breaks
• Seafloor spreading


  Happens at the mid-oceanic ridge where a divergent boundary is causing two plates to move away from one another, resulting in spreading the seafloor, as the plates move apart, new material wells up and cools onto the edge of the plates
• Mantle convection


  The slow, churning motion of Earth's mantle, carrying heat from the lower mantle and core to the lithosphere and recycling lithospheric materials back to the mantle
• Earth is not growing despite seafloor spreading because of subduction process that happens in the Pacific Ocean
• The newest, thinnest crust on Earth is located near the center of mid-ocean ridge, and the age, density, and thickness of oceanic crust increases with distance from the mid-ocean ridge
• How we know the age of the seafloor

  The new oceanic crust forms continuously at the mid-ocean ridges, and as it cools down, it records the magnetic field during its formation, the two parts of the oceanic plate are pulled apart, and magnetic stripes become older as they move away from the mid-ocean ridge
• Through most of geologic time, the ocean basins have both grown and been consumed as plate tectonics continued on Earth, the latest phase of ocean basin growth began just less than 200 million years ago with the breakup of the supercontinent Pangea
• Ocean basins


  Formed geologically of oceanic (basalt) crust, in contrast to continental (granite) crust that forms the Earth's major land masses
• Plate Tectonics


  • A unifying theory that states that the Earth is composed of lithospheric crustal plates that move slowly, change size, and interact with one another, creating three types of tectonic boundaries: convergent, divergent, and transform

  
• Oceanic basins


  Separate basins such as the Mediterranean, Tasman, Coral, Caribbean, and the Red Seas
• Shelf seas and gulfs

  Perched on continental crust (e.g., the North Sea, Arafura Sea, Baltic Sea, Yellow Sea)
• Transform plate boundary


  • Two plates sliding past each other
• Main types of plate boundaries

  • Divergent
  • Convergent
  • Transform

  
• Plate Tectonics


  A unifying theory that states that the Earth is composed of lithospheric crustal plates that move slowly, change size, and interact with one another

  
• Movement of plates creates three types of tectonic boundaries

  1. Convergent (plates move into one another)

  2. Divergent (plates move apart)

  3. Transform (plates move sideways in relation to each other)

  
• Plate boundaries lead to the formation of folds, faults, trenches, volcanoes, rift valleys, and mountain ranges

  
• Divergent boundary


  Two tectonic plates move away from each other, earthquakes are common and magma rises from the Earth's mantle to the surface, solidifying to create new oceanic crust

  
• Convergent boundary


  Two plates come together, the impact can cause the edges of one or both plates to buckle up into a mountain ranges or one of the plates may bend down into a deep seafloor trench, a chain of volcanoes often forms parallel to convergent plate boundaries and powerful earthquakes are common

  
• How plates can move relative to each other

  • Divergent (two plates move away from each other)
  • Convergent (two plates move towards each other)
  • Transform (two plates slip past each other)
• At convergent plate boundaries, oceanic crust is often forced down into the mantle where it begins to melt, magma rises into and through the other plate, solidifying into granite, the rock that makes up the continents

  
• Transform plate boundary


  Natural or human-made structures that cross a transform boundary are offset—split into pieces and carried in opposite directions, rocks that line the boundary are pulverized as the plates grind along, creating a linear fault valley or undersea canyon, earthquakes are common along these faults

  
• Relative dating


  Used to arrange geological events, and the rocks they leave behind, in a sequence, cannot provide actual numerical dates of rocks
• Principles of relative dating

  • Law of superposition (top layer is younger than the bottom layer)
  • Law of original horizontality (most sediments were originally laid down horizontally)
  • Law of lateral continuity (rock layers extend laterally or out to the sides)
  • Law of cross-cutting relationship (fault lines and igneous rocks are younger features that cut through older features of rocks)
• Absolute dating


  Also called radiometric dating or radioactive dating, a method used to determine the age of rocks by measuring its radioactive decay
• Absolute dating methods


  • Radiocarbon dating for organic remains (up to 65,000 years)
  • K-Ar dating and U-Pb dating for volcanic rocks (up to five billion years)