Lecture Summary (2/25, 2/27, and preview 3/4)
Our own Earth’s interior structure, and surface features will be compared to those found
on other planets and moons. Seismic waves are used to probe the Earth's internal structure. It
was discovered that the outer core is molten. The average density of Earth is 5.5 grams per cubic
centimeter. Evidence was given to support the premise that the Earth is differentiated. Moving
metallic material in Earth’s core generates the Earth’s magnetic field. A demonstration was done
showing that moving electrons generate a magnetic field. Surface features comparable to those
found on other planets were highlighted. The theory of continental drift involving plate motions
was introduced. Most of the surface features found on Earth are the result of plate motions.
Preserved impact craters are rare on Earth due to geological activity, the presence of an
atmosphere and erosion. Earth’s atmosphere is unlike that of any other planet in the Solar
System.
The Moon, our nearest neighbor in space, has been studied extensively, including 6
Apollo manned landings. The results were summarized in the areas of interior, surface features,
and atmosphere (in this case, lack of an atmosphere). A video was shown featuring astronauts on
the Moon. A new theory for the Moon’s origin was developed after the Apollo landings. A video
showed a computer simulation of the event.
Our survey of the planets in the Solar System began with Mercury, the planet closest to
the Sun. At best, Mercury is visible shortly after sunset or shortly before sunrise. Not much was
known about this planet before Mariner 10 flew by in 1974. The spacecraft photos revealed a
very heavily cratered surface. Details regarding surface features, this one spacecraft provided
atmosphere, and interior.
Venus is sometimes referred to as Earth's twin. U.S. and Soviet spacecraft have visited
Venus numerous times since 1962. The surface of Venus has been exposed through the use of
radar mapping. A video presented results of this technique. Based on crater densities, volcanic
lava flows on Venus have occurred rather recently, some within the last 10 million years.
Scientists aren't sure if the volcanoes on Venus are still active. There is no detectable magnetic
field, yet the density of Venus would indicate a metallic core; but perhaps the slow rotation
doesn't provide enough motion. Scientists do not yet have a good model for the interior of
Venus.
The atmosphere of Venus is dominated by carbon dioxide and the surface pressure is
"crushing." The tremendous atmosphere on Venus has led to a runaway greenhouse effect. The
greenhouse effect was explained, with a diagram. Carbon dioxide and water vapor are two
common atmospheric greenhouse gases that inhibit the infrared radiation emitted by the surface
of a planet from escaping into space directly.
Mars has long been recognized as the planet most like Earth, holding hopes of Martian
life. The "canals" drawn by Schiaparelli and Lowell are now known to be optical illusions,
largely due to "seeing" conditions through our atmosphere. Seasonal dust storms explain the
dark markings which were once believed to be growing vegetation. Surface conditions on Mars
today are very inhospitable to life. Spacecraft observations have revealed the largest volcanoes
and fault features in the Solar System on Mars. There is also evidence that water once flowed
across the Martian surface indicating a wetter, warmer Mars with greater atmospheric pressure in
the past. Currently Mars is locked in an extended ice age.
TERMS: seismic waves, continental drift, plate tectonics, impact craters, lunar maria,
lunar highlands, Apollo mission, Mariner 10, scarp, greenhouse effect, greenhouse gases,
transparent, opaque, visible light, infrared radiation, radar mapping, shield volcanoes, Magellan
mission, rift valley, runoff channels, Viking mission, Mars Pathfinder, Mars Global Surveyor,
Mars Odyssey
QUESTIONS:
1. How did geologists obtain the information necessary to draw the diagram in the book
showing Earth's interior?
2. Why does the Earth have a magnetic field?
3. What observations support the theory of continental drift?
4. Explain why the surface of the Moon looks so different compared to the surface of the
Earth.
5. Summarize what is known about Mercury.
6. How are Earth and Venus similar? How are they different?
7. Describe how a planet's surface temperature can be elevated by the greenhouse effect.
Be able to use a diagram to help in your explanation.
8. How has the surface of Venus been mapped? What discoveries were made?
9. Describe the observations made by spacecraft sent to Mars.
10 What evidence exists to support the hypothesis that water once flowed over Mars?
11. How does the Martian surface compare to Earth's surface?
12. Why are Martian volcanoes so much larger than those on Earth?