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OUR HOME PLANET, EARTH
• Our Earth is about average among the planets in the Solar
System, in many respects:
– Earth is the largest and most massive of the four terrestrial planets,
but smaller and less massive than the four giant, or Jovian, planets.
– Earth is third in distance from the Sun among the four terrestrial
planets.
– Earth has a moderately dense atmosphere; 90 times less dense
than that of Venus but 100 times denser than that of Mars.
• Earth is also unique in many respects:
– Earth is the only planet with liquid water on its surface.
– Earth’s atmosphere is the only one having a significant (21%)
proportion of molecular oxygen.
– Earth is, to our best current knowledge, the only planet in the solar
system having living organisms.
– Earth is the only terrestrial planet having a moderately strong
magnetic field.
– Earth is the only terrestrial planet having a large satellite.
THE SOLID EARTH
• The field of geology is concerned with the study of the
structure, history, and activity of the solid Earth, including its
interactions with the atmosphere, hydrosphere, cryosphere, and
biosphere.
• The structure of the body of the solid Earth contains four major
zones: the core (which is divided into inner and outer zones),
the (upper and lower) mantle, the asthenosphere, and the
lithosphere.
• The structure of the outer zones is not uniform and fixed over
the surface of the Earth, but shows much variability with position
and time.
• The field of plate tectonics deals with this spatial and temporal
variability.
• Geological phenomena such as earthquakes, volcanoes, and
continental drift are accounted for by plate tectonics.
Internal Structure of the Solid Earth
Stanley, 1989, p. 14
Press & Siever, 1982, p. 117
PLATE TECTONICS IN EARTH SCIENCE
• The theory of Plate Tectonics, which was not generally
accepted until the mid-20th Century, explains a great
many features of Earth’s current activity and past history
which were previously seemingly unrelated.
• Several lines of evidence indicate that the continents as
they now exist have moved large distances over the last
few hundred million years, both relative to each other
and relative to the north and south poles of Earth’s
rotation axis.
• According to Plate Tectonics, Earth’s lithosphere is
made up of individual plates which “float” on a semimolten asthenosphere.
PLATE TECTONICS IN EARTH SCIENCE
• The motions of the lithospheric plates are driven by
convection currents in the asthenosphere.
• The mid-Atlantic “rift zone”, which includes the volcanic
island of Iceland, is a region of upwelling of molten rock
from the asthenosphere, which also results in a widening
separation of the Americas from Europe and Africa.
• When tectonic plates collide with each other, one may be
“subducted” beneath the other, or the two may merge.
• Plate tectonics also explains other Earth activity, such as
volcanoes, earthquakes, and orogenisis (mountain
building).
Stanley, 1989, p. 166
Press & Siever, 1984, p. 446
Diagram of Lithospheric Plates and Their Interactions
VOLCANIC ACTIVITY
• Volcanic activity, the production of molten rock (lava) and its
eruption to Earth’s surface (on land or in the oceans) is one
manifestation of tectonic activity.
• Molten rock is produced as a result of the following two major
types of plate motion:
– Separation (moving apart) of two crustal plates, which allows
molten rock to rise to the surface between them.
– Collision of two crustal plates, with one moving beneath the other
(subduction), resulting in the creation of molten rock from surface
materials on the subducted plate.
• Volcanic activity in Iceland and elsewhere in the mid-Atlantic is
due to crustal spreading (the mid-Atlantic rift).
• Volcanic activity near the west coasts of North and South
America is due to subduction of Pacific Ocean plates beneath
the west edges of the continents.
• Some volcanic activity, such as in the Hawaiian Islands, is not
directly the result of plate motions.
Volcanic Activity due to Plate Spreading
Volcanic Activity due to Plate Subduction
Structure of a Volcano
Volcanoes of the U.S. Pacific Coast
Stages of Eruption of Mt. St. Helens, 1980
Eruption of Mt. St. Helens Volcano, May 1980
Post-Eruption View from LandSat
View of the Volcano Anak Krakatau, in the Sunda Strait, Indian Ocean,
Indonesia; Taken by the Ikonos Satellite, June 11, 2005
EARTHQUAKES
• Earthquakes are due to sudden motions of crustal plates, as a
result of fracture or slipping of one plate relative to another.
• Zones of high probability of earthquakes (seismic activity) are, like
volcanic activity, usually near plate boundaries or subduction
zones.
• The shaking motion of earthquakes is due to the propagation of
two types of seismic waves: longitudinal waves, and transverse
waves.
• Longitudinal waves, like sound waves, can propagate through
solids and liquids.
• Transverse waves can propagate only through solids.
• Monitoring of seismic waves at large distances from earthquake
centers have revealed details of Earth’s inner structure, including
the fact that the outer core is molten (does not transmit transverse
seismic waves).
Press & Siever, 1984, p. 402
Earthquake Resulting from Transform Fault Slippage
Epicenter
Focus
Fault
Press & Siever, 1984, p. 400
Press & Siever, 1984, p. 398
Anchorage, Alaska Earthquake - Good Friday, 1964
Loma Prieta (California) Earthquake, 1989
Production of Tsunami Waves by Earthquakes
December 26, 2004 Earthquake-Generated Tsunami
(Red = Wave Heights Measured by Jason 1 Satellite)
Longitudinal Waves
Transverse Waves
Propagation of Seismic Waves Through Earth’s Interior
Longitudinal waves travel through
both solids and liquids.
Transverse waves travel through
solids only.
CONTINENTAL DRIFT
• Another aspect of the theory of plate tectonics, is that it indicates
that the continents of Earth’s crust move (relative to the main
body of Earth) and change shape with time.
• This explains the similarity of extinct animal and plant fossils on
adjacent continents (such as South America and Africa) which
are now separated by large bodies of water.
• Magnetized minerals and their orientations relative to Earth’s
magnetic poles also provide evidence for continental drift.
• Some continental areas now close to the equator give evidence
of at one time being covered with glaciers (which would have
required them to be closer to the poles).
• This “continental drift” is also consistent with the currently
observed plate motions which give rise to volcanic and seismic
activity.
Fossils of now-extinct animal species in land areas now separated by
oceans provide evidence of continental drift.
Earth’s Land and Oceans 200 Million Years Ago
Pangaea
Tethys Sea
200 Million Years Ago
50 Million Years Ago
150 Million Years Ago
100 Million Years Ago
Present
Zones on Present-Day Continents with Evidence
of Glaciation from Pangaean Times
300 M years ago
Present
Mountain Building Processes
Press & Siever 1984, p. 498
Space-Based Remote Sensing of the Solid Earth
• Observing the solid Earth from space has many unique advantages in
comparison to ground- and aircraft-based measurements.
• In particular, satellites in appropriate orbits can make observations of
the entire Earth, at repeated intervals and/or over long periods of
time, using a variety of instrumentation and observing techniques.
• The first major satellite program dedicated to solid Earth observations
was the LandSat series, beginning in the mid-1960’s.
• The most recent, and most capable, mission of this type is the
currently operational Terra satellite, launched in February, 2000.
• Terra is the first of three major Earth science satellites, constituting
NASA’s Earth Observing System (EOS).
• More recently launched sister satellites, in this three-satellite series,
are the Aqua satellite (for studies of Earth’s oceans and other water
bodies) and the Aura satellite (for studies of Earth’s atmosphere from
above).
The Terra Earth Observing Satellite Mission
• The Terra mission (EOS-1) was
launched February 24, 2000.
• The primary scientific objectives of the
Terra mission include studies of the
following:
–
–
–
–
•
What are Aerosols?
Changing Global Cloudiness
Why Isn’t Earth Hot as an Oven?
Changing Global Land Surface
The Scientific Instruments on Terra are the following:
- Advanced Spaceborne Thermal Emission and Reflection Radiometer
(ASTER)
- Clouds and Earth’s Radiant Energy System (CERES)
- Multi-angle Imaging Spectroradiometer (MISR)
- Moderate-resolution Imaging Spectroradiometer (MODIS)
- Measurements of Pollution in the Troposphere (MOPITT)