The Earth in Context, Earth's Atmosphere, Heating and Temperature

 

 

Solar System

  • Our sun is a star
  • What is our sun's name?

Universe

  • How old? 13.8-Ga
  • My office address:
    • Universe
    • Virgo Supercluster (galaxy clusters)
    • Local Group Cluster (galaxies)
    • Milky Way (our galaxy)
    • Solar System
    • Earth (third rock from the sun)
    • North America
    • United States
    • New York
    • 695 Park Ave.
    • North Building
    • Room 1006B

 

Earth's Magnetic Field

  • What is a magnetic field?
  • Dipole
  • Magnetic vs. Geographic Pole
  • Solar wind
  • Magnetosphere
  • Van Allen radiation belts

 

Earth Systems

  • Geosphere
  • Hydrosphere
  • Atmosphere
  • Biosphere

 

Geosphere

  • What does the Earth's surface consist of?
    • Organic chemicals
    • Minerals
    • Rocks
      • Igneous
      • Sedimentary
      • Metamorphic
  • 93% of the Earth's mass is made of four elements:
    • Iron (35%)
    • Oxygen (30%)
    • Silicon (15%)
    • Magnesium (13%)
  • The most common rock type are silicate rocks. There are four types based on percentage of silica (SiO2) relative to the percentage of iron oxide (FeOx) and magnesium oxide (MgOx):
    • felsic (ex.: granite, has large grains)
    • intermediate (ex.: basalt, small grains)
    • mafic (ex.: gabbro, large grains)
    • ultramafic (ex.: peridotite, large grains)

 

As silica content decreases and the percentage of iron/magnesium oxides increases, the density of the rock increases:

 

 

 

Energy & Exchanges in Earth Systems

  • Earth systems are in constant motion.
  • Land, oceans and the atmosphere move and exchange material and energy.
  • The energy that drives these motions comes from three sources:
    • internal energy
      • collision of planetesimals converted kinetic energy to heat
      • compression of matter increased temps
      • radioactive decay
    • external energy & gravity
      • solar energy warms causing convection along with gravity

 

 

Earth's Interior

  • measurements of the Earth's gravitational pull and determining its volume allows calculation of Earth's average density.
  • surface rocks have a density lower than the average
  • core must be much higher density rock.... high metal content
    • since the Earth is close to a sphere the metal must be concentrated near its center otherwise, centrifugal force would pull the equator outward and Earth would be somewhat disk-shaped.
    • the interior must be mostly solid, because if it weren't, the land surface would rise and fall due to tidal forces much more than it does

 

 

 

Seismic Waves

  • vibrations or shocks that pass through the Earth from a location where rock suddenly breaks and slips along a fracture call a fault

 

  • you can simulate the process of generating vibrations, at a small scale, when you break a stick and feel the snap in your hands

 

 

  • where seismic waves reach the surface of the Earth and cause it to shake, people feel an earthquake
  • seismic waves travel at different velocities through different materials, and bend or reflect when they reach boundaries between different materials.
  • seismometers are needed to study these waves and are placed at various locations on Earth's surface
  • seismometers allow us to:
    •  pinpoint the depth of boundaries between layers
    • the ID sub-layers within the major layers
    • determine whether layers are solid or liquid

 

 

Pressure & Temperature inside the Earth

  • mass of overlying rock increases with depth, so the pressure within the Earth also increases with depth
  • in solid rock the pressure at 1km is about 300 atm
  • at Earth's center the pressure probably reaches about 3,600,000 atm
  • temperatures also increase with depth
  • at 4 km below the surface, the depth of the world's deepest gold mine, the temperature is 140oF
  • in the upper part of the Earth's crust the geothermal gradient is 20oC to 30oC per kilometer
  • at greater depths the gradient decreases to less than 10oC/km
  • the mantle-core boundary temperature is about 3,500oC
  • calculations suggest the Earth's core temperature is about 4,700oC, not much cooler than the surface of the sun (5,500oC)

 

 

Basic Characteristics of the Earth's Layers

 

The Crust

  • Andrija Mohorovicic (1857 - 1936) in Croatia discovered the velocity of earthquake waves suddenly increased at a depth of tens of kilometers beneath the Earth's surface
  • he suggested that this increase was caused by an abrupt change in the properties of rock
  • later studies showed this change occurs almost everywhere but at different depths
  • the area of change is deeper under continents than beneath oceans
  • geologists now consider this change to define the base of Earth's crust and refer to it as the Moho
  • the relatively shallow depth of the Moho (7 to 70 km, depending on location) as compared to the radius of the Earth (6,371 km), emphasizes that the crust is very thin

 

  • the crust is not just cooled mantle
  • it consists of a variety of rocks that differ in composition (chemical makeup) from mantle rock

 

  • oceanic crust is only 7-10 km thick
    • the top is composed of a 1 km thick layer of sediment composed of clay and tiny shells
    • next is a layer of basalt and below that a layer of gabbro

     

  • continental crust is generally 35 to 40 km thick but it varies considerably (25 to 70 km)
    • contains a greater variety of rocks from mafic to felsic
    • on average, upper continental crust has a felsic (granite-like) to intermediate composition
    • is less dense than oceanic crust

 

 

The Mantle

  • is a 2,885 thick layer surround the Earth's core
  • consists entirely of ultra-mafic (dark & dense) rock called peridotite
  • peridotite is rare at the surface but is the most abundant rock on the planet
  • the mantle is mostly solid but is so hot that it's soft enough to flow
  • flow rates are less than 15 cm/year (6 inches/year)
  • soft does not mean liquid
  • it means that over long periods of time mantle rock can change shape without breaking
  • this in known as plasticity
  • because of its softness, the mantle can undergo convection very slowly
    • warmer rock rises
    • cooler rock sinks

 

 

The Core

  • very high density of iron alloy
    • 4% nickel
    • up to 10% oxygen and/or silicon or sulfur

     

  • outer core
    • liquid because the temp is so high that no even the great pressures cannot keep atoms locked in a solid framework
    • this liquid iron alloy core generates Earth's magnetic field

    inner core

    • solid iron alloy because of much higher pressure

 

 

 

 

 

 

The Lithosphere & Athenosphere

  • a different way of looking at Earth layers, either rigid or plastic materials

 

  • lithosphere: the outer 100 to 150 km of the Earth is relatively rigid
    • consists of the Earth's crust plus the relatively cool upper mantle
  • asthenosphere: found under the lithosphere where the rock is plastic when temps reach about 1,280oC

 

 

The Earth's Atmosphere

Heating Earth's Surface and Atmosphere

Temperature