The Dynamic Earth

What does dynamic mean?

• Ever changing in varying degrees of intensity.

The Sources of Energy for the Earth

• What is the source of the Earth’s dynamic nature?

• A constant flow of energy.• External Sources of Energy

– Sunlight (Light Energy)

• Internal Sources of Energy– Leftover thermal energy from the Earth’s formation– Friction from the movement of the lithospheric plates– Decay of radioactive elements (Uranium, for example)

The Earth’s Atmosphere

• Layers

• Composition

• Evolution

Atmospheric Layers

• Four Layers– Thermosphere (outermost layer, receives intense solar

radiation)– Mesosphere (coldest layer)– Stratosphere (contains the ozone layer, warmer due to

absorption of ultra-violet light)– Troposphere (the weather layer, the densest layer)

• Also, the Ionosphere (forms due to the interaction of cosmic radiation from the Sun with the faint nitrogen and oxygen concentration in the thermosphere)

Atmospheric Composition

• Nitrogen (N2) (78%)

• Oxygen (O2) (almost 21%)

• Argon (almost 1%)• Small amounts of other gases (0.1%), including

– Water vapor

– Carbon Dioxide

– Methane

– Layer of Ozone (O3)

Atmospheric Evolution

• Primordial atmosphere contained mostly carbon dioxide and nitrogen, with some ammonia and hydrogen—volcanic gases.

• 2.5 billion years ago, a change occurred, plant cells algae, began to consume carbon dioxide and give off oxygen (photosynthesis)

• Atmosphere gradually filled with oxygen• 350 million years ago…basically same level of

oxygen as today.

Earth’s Protection System

• Ultra-violet light shield (ozone layer)

• Thermal insulating blanket (greenhouse gases in the atmosphere)

• Solar wind blocker and atmospheric erosion protector (Earth’s magnetic field or magnetosphere)

Without the Ozone Layer

• Eventually, no terrestrial life (DNA destroyed)

Without the Greenhouse Gases

• Earth would much colder and iced over (-27 degrees C)

Without the Magnetic Field

• Atmosphere would be eroded by the solar wind, and cosmic radiation (electrons and protons from the Sun) would harm living organisms.

Greenhouse Effect

• The surface of the Earth is heated by visible light from the Sun. The Earth then radiates thermal energy as infrared light.

• The presence of greenhouse gases, CO2 and H2O and methane (CH4) and a few other trace gases, serve to trap or absorb some of the infrared light radiated from the Earth’s surface.

• Visible light’s wavelength is too short to be absorbed by these greenhouse gases, but infrared light’s wavelength is longer and can be absorbed.

• This interaction increases the surface temperature of the Earth.

Global Warming

• The greenhouse effect is a good thing for life. However…

• …Any increase in the greenhouse gas concentration (in parts per million) will cause more infrared light radiated from the Earth’s surface to be trapped, causing the Earth to become warmer.

• The recent increase in the concentration of carbon dioxide is due to the combustion of hydrocarbon- rich fossil fuels, such as coal, petroleum and natural gas. (cause: see Industrial Revolution)

Ozone Layer

• Ozone absorbs the majority of incoming ultra-violet light from the Sun.

• Ozone is composed of three oxygen atoms, and is toxic to humans.

• Ozone holes or thinning is primarily caused by CFCs (chlorofluorocarbons)—used in aerosol sprays, now banned worldwide.

• Some evidence of the “healing” of the ozone layer is observed, however, it is estimated that it should recover in another 2-3 decades without CFCs.

Earth’s Magnetic Field

• The source of the Earth’s magnetic field--The Dynamo Theory: The rotation of the Earth causes the electrons in the outer liquid core (composed of molten iron and some nickel) to move. Moving electrons, as you recall, produce magnetic fields (that is, electromagnetism).

Atmosphere Pressure and Wind

• What causes the wind?• Differences in atmospheric pressure.• What causes differences in atmospheric pressure?• Differences in the heating of the Earth’s surface.• What causes differences in the heating of the

Earth’s surface?• Three reasons

– Angle of the sunlight striking the Earth’s surface– Duration of the sunlight– Ratio of sunlight being reflected vs. absorbed

Wind Belts and the Coriolis Effect

• Without the rotation of the Earth, two main convection cells would operate, from equator to poles.

• With the rotation, the winds are deflected either east or west, due to the Coriolis effect.

• Winds from the poles are deflected to the west, winds from the equator are deflected to the east.

• These are the prevailing winds (trade winds, westerlies and polar easterlies)

Ocean Currents

• Surface ocean currents circulate throughout the Earth.

• Surface ocean currents are produced by the prevailing wind belts.

Earth’s Thermal Energy Cycle

• Excess heat (thermal energy) accumulates in the vicinity of the Earth’s equator.

• This heats the atmosphere and the Earth’s oceans.

• Heat or thermal energy is moved away from the equator to the poles to equalize the temperature of the Earth—Earth strikes a balance.

Earth’s Thermal Energy Cycle

• How does the Earth correct for this imbalance in thermal energy (hot equator, cold poles)?– Winds form a convection current from the equator to

poles (warm air moves to the poles, is cooled and returns to be heated).

– Ocean currents carry warm water to the poles and, when cooled, the cooler water from the poles circulates to the equator to be heated again.

The Earth

• The layers of the Earth (Crust, Mantle and Core)• Why layered?

– Differentiation (the settling of heavier elements, such as iron, towards the center of the Earth, less dense iron rich mantle rock “floats” on the dense iron core)

– Geochemistry (hot inner iron core under pressure can remain in solid state; should also see a lowering of pressure away from center of Earth where solid iron core changes to liquid molten iron core)

– Geophysics (s-waves or transverse seismic waves cannot travel through liquids, and s-waves cannot penetrate the outer core; thus, the outer core must be liquid)

Fig. 1-10c, p. 14

Fig. 1-10, p. 14

Differentiation

Fig. 1-11, p. 15

Fig. 9-21, p. 210

Why does the surface of the Earth Constantly Change?

• Water Cycle (weathering, erosion and transport of weathered rock sediments)

• Rock Cycle (melting of rock produces igneous rocks, weathering of igneous rock produces sedimentary rocks, and high pressure and temperature without melting produces a metamorphic rock.)

• Plate Tectonics (the Earth’s rigid lithosphere—crust + top part of the mantle is broken into plates that move into, away from or across each other)

Fig. 1-15, p. 19

What is Plate Tectonics?

• The rigid lithospheric plates move over the plastic flowing part of the mantle called the asthenosphere.

• As heat (thermal energy) from the core moves towards the Earth’s surface (heat flows from hot to cold), this produces convection currents in the mantle, which move the asthenosphere and drag the rigid lithospheric plates across the Earth.

Fig. 1-3, p. 5

Plate Boundaries

• Divergent Plate Boundary (oceanic ridges and undersea volcanoes—see the Atlantic Ocean)

• Submergent Plate Boundaries (trenches and volcanic mountain chains—see the Andes Mountains); also known as a convergent plate boundary.

• Transform plate boundaries (side-by-side plate motion—see the San Andreas Fault

Fig. 1-13, p. 17

Fig. 1-12, p. 15

The Mechanism for Plate Motion is Convection in the Mantle

Fig. 1-17, p. 20

Fig. 1-14, p. 18

Three types of plate boundaries

1. Divergent plate boundary 2. Convergent Plate Boundary 3. Transform Plate boundary

Evidence for Plate Tectonics

• Geographic fit of continents

• Flora and fauna associations

• Paleomagnetism patterns associated with the iron in the spreading sea floor.

• Location pattern of volcanoes, earthquakes and mountains

Fig. 2-4, p. 30

Fig. 2-5, p. 31

Fig. 2-6, p. 31

Fig. 2-7, p. 32

Fig. 2-8a, p. 34

Fig. 2-8b, p. 34

Fig. 2-10, p. 35

Fig. 2-11, p. 36

Who came up with this idea of Plate Tectonics?

• Alfred Wegener first suggested moving continents in his Continental Drift theory.

• But he had no mechanism; he thought that perhaps the continents slowly plowed through the oceanic crust.

• Hess in 1960s began to observe age differences in sea floor core samples collected in the Atlantic Ocean. Youngest crustal rock was closest to the ridge and the oldest crustal rock was furthest away from the ridge (true for both sides of the ridge!)

• This became known as sea floor spreading.

Fig. 2-3, p. 29

Fig. 2-12, p. 36

Fig. 2-13, p. 37

Fig. 9-5, p. 191

Fig. 2-14, p. 38

Significance?

• Continental crust is less dense than oceanic crust, and literally floats in the oceanic crust.

• The lithospheric plate consists of continental and/or oceanic crust and the very top of the mantle.

• Continents are carried with the oceanic crust and top part of the mantle.

• This can lead to the formation of trenches, ridges, and mountain chains.

Mt. Everest is still rising?

• Himalayan Mountains represent a subduction plate boundary, where an ocean separated two continents. As the ocean closed, the two continents collided, which produced the highest mountain chain in the world today, and is still pushing the continental crust upward.

Fig. 2-15, p. 40

Fig. 2-17, p. 42

Fig. 2-18, p. 42

Seismic Waves

• Seismic waves are produced by earthquakes when stresses build up by moving plates are suddenly released.

• Interior waves produced by this disturbance include longitudinal waves or p-waves and transverse waves or s-waves.

• P-waves are faster than s-waves, and can travel through solids or liquids. S-waves cannot travel through liquids.

• The epicenter and focus of an earthquake can be calculated using seismic data from at least three seismic stations.

Fig. 9-21, p. 210

Fig. 9-4, p. 191

Fig. 9-8, p. 194

Fig. 9-9, p. 195

Fig. 9-10, p. 196

Fig. 2-19, p. 43

Fig. 2-23, p. 46