In Class:
Question to Ponder
Which of the following scenarios is an example of uniformitarian evolution?
- a) The creation of the Atlantic Ocean as the continents drifted apart.
- b) The formation of the Moon.
- c) "Nuclear winter" -- climate change caused by fallout from nuclear war.
- d) The change in the landscape around Mt. Saint Helens due to its
1980 volcanic eruption.
How Much is Mars Like Us?
- Smaller -- 10% of Earth's mass; half of Earth's radius
- very thin atmosphere (pressure is 1% of Earth's atmosphere)
- Cold -- maximum temperatures ~50 F
- Dry -- no liquid surface water
Imaginations run wild
- Studied telescopically, since we can see to its surface.
- in 1800's Schapparelli charted surface features, and called them
"canali" -- Italian for "channels"
- Misinterpreted as "canals" and quickly became the basis for
believing that an advanced civilization existed on Mars.
- Canals presumably brought water from ice caps to thirsty desert
cities.
- Percival Lowell dedicated a great deal of money to the study of
canals, and built the Lowell Observatory in Flagstaff, AZ.
- People realized by the 1930's that the "canals" were not the work
of martians, and interest in Mars waned.
Exploration of Mars by Spacecraft
- Mariner 9 (1971) discovers real channels on martian
surface -- too small to be seen form Earth, but quite likely carved by
water.
- Suggests that liquid water did flow on Mars in the distant
past.
- Imaged massive volcanoes (Olympus Mons -- 78,000 feet tall), and
deep canyon (Valles Marineris -- 3,000 miles long).
Why is There No Water Now?
- Liquid surface water requires higher temperatures and higher
atmospheric pressures than currently on Mars.
- Approximately 3 billion years ago, Mars had a more substantial
atmosphere.
- With a thick atmosphere, the greenhouse effect raised the surface
temperatures to levels where water wouldn't freeze.
- Also, with a thick atmosphere, liquid surface water wouldn't
evaporate as fast.
- The atmosphere was generated from outgassing volcanoes, which in
turn were driven by the planet's hot interior.
- The interior cooled (quickly, because it's a small planet), and
the volcanoes stopped.
- Because of its low surface gravity, Mars was unable to hold its
atmosphere. Molecules had enough energy to escape the gravitational
grip and drift out into space.
- Mars' atmosphere became thinner and thinner, and the surface cooled.
- Water froze or evaporated.
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