Earth

Major characteristics

• Diameter = 12,756 km

• Shape - not a perfect sphere. Flattened at poles, bulging at equator.

• Density = 5.5 g/cm3 overall.

• Temperature fairly constant over billions of years; water has remained liquid.
  • Maximum = 140 degrees F
  • Minimum = -130 degrees F

Interior

1. Crust - silicate rock (Si, O, Al, Ca, Na, K, Fe, Mg). Averages about 15 km thick.
   • Oceanic Crust is 5 - 10 km thick. Basalt. Fine-grained dark igneous rock.
   • Continental Crust is 30 - 50 km thick. Granite. Coarse-grained light-colored igneous rock.

2. Mantle - solid rock that flows under high pressures and temperatures. Fe and Mg silicates such as peridotite (olivine-rich), eclogite, and kimberlite. About 3000 km thick.

3. Outer core is molten iron and nickel.

4. Inner core is solid iron and nickel. (Similar to iron meteorites.)

The Earth's magnetic field is generated by rotation of inner core and convection in outer core.

Magnetic field also responsible for aurora borealis.
Charged particles from sun follow magnetic field lines. Particles collide with molecules in atmosphere and cause them to emit light.
Elecxtrons in orbit around atoms are "excited".

Rocks and Minerals

Types of rocks:

1. Igneous
2. Sedimentary
3. Metamorphic

Studying the Earth's Interior

1. P-waves - (primary, pressure, push-pull).
   Travel through solid and liquid.

2. S-waves - (secondary, shear, shaking).
   Travel through Solids only.

Detect seismic waves with seismographs.

Calculate the velocity of seismic waves by measuring travel times and distances.
Seismic waves travel faster in denser rock.
Average density for the Earth = 5.5 g/cm3

• Crust = low density (3 g/cm3)
  
  • Continental - Seismic wave velocity = 6 km/sec
  • Oceanic - Seismic wave velocity = 7 km/sec

• Mantle = 4.5 - 5 g/cm3. Seismic wave velocity = 8-12 km/sec

• Core = 12 g/cm3. Seismic wave velocity = 11-12 km/sec in inner core.

Sharp jumps in seismic velocity are called discontinuities.

Mohorovicic Discontinuity separates crust and mantle.

Origin of layering and discontinuities

1. Cold accretion, heating, and differentiation
2. Hot accretion and crystallization of materials in sequence

Plate Tectonics

Mantle is solid that flows.

Convection in mantle responsible for moving plates.

Evidence for plate tectonics:

• Fit of continents
• Faunal similarities
• Fossil evidence
• Similariies of rock sequences and structures on continents when fit together
• Magnetic stripes on sea floor
• Paleomagnetic pole positions are same when continents are fit together

Plate movements

1. Divergent (spreading) - mid-ocean ridges and rift valleys (E. Africa)
2. Convergent (colliding) - deep sea trenches (subduction zones), mountain belts (continental collision)
3. Transform (sliding past one another)

Earthquakes occur at plate boundaries.

Volcanoes occur at plate boundaries and also at hot spots.

Atmosphere

Atmosphere protects Earth from ultraviolet radiation. Ozone layer.

Presence of oxygen is unique in the solar system.
Due to photosynthesis.

Carbon dioxide increasing. Increased almost 20% in last 80 years. Why?

Greenhouse Effect.

This page was created by Pamela J. W. Gore
pgore@gpc.edu
DeKalb College
February 19, 1996