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Lec 20: 9 November 2011 Chap 9: The Earth. II. Changing Surface LAST TIME - Earth I. Overview of Earth as a Planet: Interior
• What’s inside, and how do we know?
TODAY - Earth II. Earth’s Changing Surface • Effects of gradual cooling of a planet • 2 Kinds of Earth Crust • Geological Activity • Plate Tectonics
NEXT - Surfaces of the Terrestrial Planets (Read Chap 11)
THEN – Atmospheres and Climate of Terrestrial Planets – Interactions Between Interior, Surface, Atmosphere, and Life – Evolutionary, Cataclysmic, and Human-Induced Changes
Global Properties of the Terrestrial Planets
Mercury Venus Earth Moon Mars
Mass 0.06 0.82 1 0.01 0.11 Diameter 0.38 0.95 1 0.27 0.53 Density (g/cc) 5.4 5.2 5.5 3.3 3.9 uncompressed... 5.2 4.3 4.4 3.3 3.8
Gravity 0.38 0.91 1 0.17 0.38 Albedo (%) 12 59 39 11 15 Atm. Pressure 0 88 1 0 0.01 Temperature (degrees K)
103-623
733 183-333
93- 403
133- 293
A bigger planet takes longer to cool down.
Interiors of the Terrestrial Planets
Heat and Thermal Energy
• Temperature is a measure of internal energy (kinetic and potential)
• Heat is “flow” of thermal energy from high temperature to low temperature
• 3 ways: Conduction, Convection, Radiation
• Why are planetary interiors hot? – gravitational contraction (mostly for Jovian’s) – primordial heat (accretion) – radioactive decay of heavy elements
Two Types of Earth Crust
• 45% of surface • up to 3.5 billion years old
• 20 - 70 km thick • some sedimentary and
metamorphic rock • mostly granite (igneous)
• 55% of surface • < 200 million years old
• 6 km thick • some sediments (not
sedimentary rock) • basalt (igneous)
Continental Oceanic
granite solidified under high pressure; less dense than basalt
Basaltic Lava Flows in Hawaii
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Kilauea Caldera
(Hawaii)
Two Types of Crust
• 45% of surface • up to 3.5 billion years old • 20 - 70 km thick • some sedimentary and
metamorphic rock • mostly granite (igneous)
• 55% of surface • < 200 million years old • 6 km thick • some sediments (not
sedimentary rock) • basalt (igneous)
Continental Oceanic
Both types “float” on the denser, plastic-like mantle.
Continents pile up higher, heavier, and less dense.
Geological Activity
• earthquakes, volcanoes (several types), mountains (several types), island chains
• constantly changes Earth’s surface
• nothing left of “original” surface
• driven by heat from Earth’s interior
• plate boundaries : where the action is
Plate Boundaries Show Up When You Plot the Locations of Earthquakes or Volcanoes
Note: Video on your CD or the publisher’s web site.
Plate Tectonics
• “Tectonics” - reaction of planetary surface to global forces
• “Plates” (unique to Earth) – lithosphere broken into 6 major and ~10
smaller plates – not just continents – no free space between the plates – plates move laterally, driven by convection in
mantle, by a few cm each year, with new material added in (mid-ocean) rift zones
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Relative Motions of Earth’s Plates
Plate Tectonics Examples
(see videos)
Mid-Atlantic rift
Volcanic Island
Himalayas (continental plates colliding)
Sanai (continental plates rifting)
Other Features of Plate Tectonics • Super Continents
– past.... – future...
• Hot Spots – plate drifts across “plume”
that is fixed to mantle – e.g. Hawaii – there are hot spots on other
planets, too! • Buildup and Evolution of
Continental Crust – not subducted, less dense
than oceanic – older than oceanic – erosion and gradual
evolution
Bay Area in Metropolitan LA? I Hope Not! Other Features of Plate Tectonics
• Super Continents – past.... – future...
• Hot Spots – plate drifts across “plume” that is fixed to mantle – e.g. Hawaii – there are hot spots on other planets, too!
• Buildup and Evolution of Continental Crust – not subducted, less dense than oceanic – older than oceanic – erosion and gradual evolution