1. Was there ever geological activity on the Moon or Mercury
Was there ever geological activity on the Moon or Mercury? (Yes, but long ago)

2. Formation of Lunar Maria
Very large, deep crater formed by asteroid impact
Runny lava seeps through lithosphere, filling crater
Lava hardens to form darker-colored maria
Heavily-cratered early lunar surface
Some volcanic activity billion years ago must have flooded lunar craters, creating lunar maria (dark areas on Moon).
Maria have few craters  formed after Period of Heavy Bombardment ended.

3. Geologically Dead
Moon is considered geologically “dead” now because geological processes have virtually stopped (no more internal heat).
Lack of outgassing  no more atmosphere on the Moon.
Micrometeorites pulverize rock, creating fine dust.

4. Cratering of Mercury
Mercury has a mixture of heavily cratered (oldest) and smooth regions (somewhat younger) like the Moon.
The smooth regions are likely ancient lava flows.

5. Tectonics on Mercury
Mercury is also now geologically dead.
Lack of outgassing  no atmosphere
Long cliffs (hundreds of miles long, 2 miles high) indicate that Mercury shrank early in its history.

6. Mars

7. “Canals” on Mars
In 1877, astronomer Giovanni Schiaparelli used the Italian word ‘canali’ (channels) to describe features on Mars.
Unfortunately, this was mis-interpreted as “canals” in English, leading people to believe there were structures built on Mars by Martians.
Percival Lowell misinterpreted surface features seen in telescopic images of Mars.

8. Polar Ice Caps of Mars
CO2
+ H2O
CO2
Late winter
Mid-spring
Early summer
Carbon dioxide (CO2) ice (“dry ice”) of polar cap sublimates as summer approaches and condenses at opposite pole.

9. Polar Ice Caps of Mars
Residual ice of the polar cap remaining during summer is primarily water ice – water has a higher sublimation temperature than carbon dioxide.
If all water ice melted, an ocean 11-meters deep over the entire planet could be formed.

10. Dust Storms on Mars Seasonal winds can drive dust storms on Mars.
Dust in the atmosphere absorbs blue light, sometimes making the sky look brownish-pink.

11. Volcanoes…as recently as 180 million years ago, but no volcanoes are known to be active today.

12. Past tectonic activity…
Is Mars geologically active today?
Activity is probably ending right about now.

13. What geological evidence tells us that water once flowed on Mars?

14. Dry Riverbeds?
Close-up photos of Mars show what appear to be dried-up riverbeds.
Crater counts imply river beds are ~3 billion years old.

15. Erosion of Craters
Details of some craters suggest they were once filled with swirling liquid water.
Sedimentary rock laid down when crater was filled with water?

16. Eroded crater (from rainfall?)
Impact Craters on Mars
“Standard” crater
Impact into icy ground
Eroded crater (from rainfall?)

17. Which is Mars? Left (A) or Right (B)?
Martian Rocks
Which is Mars? Left (A) or Right (B)?

18. Martian Rocks
jarosite
Jarosite and hematite form in water on Earth.
Mars rovers have found rocks that appear to have formed in water  hematite “blueberries”.

19. Water on Mars! Water on Mars!
Spectra+imaging by orbiting spacecraft have just found (last Fall) evidence of hydrated salts (perchlorates) on the slopes of a crater on Mars!  liquid water must have been flowing down the slopes very recently (seasonal)

20. Climate Change on Mars
Mars has not had widespread surface water for 3 billion years, but most likely had water before that.
Greenhouse effect probably kept the surface warmer before that  lots of liquid water? (extremely likely).
Because of its smallish size, Mars lost most of its atmosphere
- low mass of Mars allowed gases to diffuse
away from atmosphere.
- little/no additional gas replenishment from
outgassing once volcanism diminished

21. If Mars Had Only Been Bigger…
The gravity of a larger Mars would have retained its atmosphere more easily
A larger Mars would have continued volcanic/outgassing activity until today (slower cooling)
A larger Mars would have a thicker atmosphere, more greenhouse effect, warmer surface  liquid water?
Would these have been our neighbors?

22. Which of the following is not evidence that liquid water existed on the surface of Mars in the distant past?
A) Hematite “blueberries”
B) Weathered craters
C) Fossilized coral reefs
D) Features that look like dried-up river beds

23. Which of the following is not evidence that liquid water existed on the surface of Mars in the distant past?
A) Hematite “blueberries”
B) Weathered craters
C) Fossilized coral reefs
D) Features that look like dried-up river beds
No evidence of any fossil life on Mars (so far).

24. What are the major geological features of Venus?

25. Radar Mapping
Its thick (90x Earth) atmosphere forces us to explore Venus’s surface through radar mapping.

26. Cratering on Venus
Venus has impact craters, but fewer than the Moon, Mercury, or Mars
Thick atmosphere burns up many smaller meteors.

27. Volcanoes on Venus
It has many volcanoes, with evidence of recent activity.
Tentative evidence for active volcanoes observed very recently.
Copious sulfur dioxide indicates outgassing is ongoing.

28. Tectonics on Venus
The planet’s fractured and contorted surface indicates tectonic stresses in the past.
Tectonic activity today? Unclear….

29. Erosion on Venus
Photos of rocks taken by landers show very little erosion (sharp edges).
Too hot for rain.
Too slow rotation (6.5 km/hr) for substantial winds.

30. Summary of Venus’s Geology
Cratering? Yes, but smaller asteroids burned up because of thick atmosphere.
Volcanism? Maybe (probably) there are active volcanoes.
Tectonics? In the past, but probably not now. A thick, dried-out hardened lithosphere?
Erosion? Not much, no liquid rain or ice, and little wind due to very slow rotation.

31. How did Venus get so hot?
The greenhouse effect on Venus keeps its surface temperature at 470°C.

32. Greenhouse Effect on Venus
Thick carbon dioxide (CO2) atmosphere (90x Earth’s pressure) produces an extremely strong greenhouse effect.
Same pressure as you would feel 1 km beneath sea level!
Earth escaped this fate because most of its carbon and water is locked up in rocks and oceans.

33. Runaway Greenhouse Effect
A runaway greenhouse effect would account for why Venus has so little water (and such a high temperature).

34. Ultimately, why doesn’t Mercury have a very thick CO2 atmosphere like Venus?
Mercury is much smaller than Venus.
Mercury is closer to the Sun than Venus.
C) There was no CO2 within the part of the solar nebula where Mercury was formed.
D) Mercury was hit by more asteroids than Venus.

35. Ultimately, why doesn’t Mercury have a very thick CO2 atmosphere like Venus?
A) Mercury is much smaller than Venus.
B) Mercury is closer to the Sun than Venus.
C) There was no CO2 within the part of the solar nebula where Mercury was formed.
D) Mercury was hit by more asteroids than Venus.
Smaller Mercury  lost internal heat  no more volcanism  no more outgassing  no atmosphere  no greenhouse effect!

36. What unique features of Earth are important for life?
Surface liquid water
Atmospheric oxygen
Climate stability
Earth’s distance from the Sun and moderate greenhouse effect make liquid water possible.

37. What unique features of Earth are important for life?
Surface liquid water
Atmospheric oxygen
Climate stability
PHOTOSYNTHESIS (plant life) is required to make high concentrations of oxygen, which produces the protective layer of O3 (ozone) in the stratosphere of Earth’s atmosphere.

38. What unique features of Earth are important for life?
Surface liquid water
Atmospheric oxygen
Climate stability
The CO2 cycle acts like a thermostat for Earth’s temperature.