1. Chapter 9 Planetary Geology: Earth and the Other Terrestrial Worlds

2. Interiors of terrestrial planets

3. Differentiation Gravity pulls high-density material to center
Lower-density material rises to surface
Material ends up separated by density

4. Lithosphere: Outer layer of rigid rock that composed of the crust and the uppermost mantle. It “floats” on softer rock below

5. Geologic Processes that Shape Surfaces
Impact cratering
Impacts by asteroids or comets
Volcanism
Eruption of molten rock onto surface
Tectonics
Disruption of a planet’s surface by internal stresses
Erosion
Surface changes made by wind, water, or ice

6. Impact Craters
Most cratering happened during the heavy bombardment (soon after solar system formed)
Craters are about 10 times wider than object that made them

7. Small craters greatly outnumber large ones
Meteor Crater (Arizona)
Tycho (Moon)
Small craters greatly outnumber large ones
Frequency of craters reveals age of surface

8. Volcanism
Volcanism happens when molten rock (magma) finds a path through lithosphere to the surface
Molten rock is called lava after it reaches the surface

9. Runny lava makes flat lava plains
Slightly thicker lava makes broad shield volcanoes
Thickest lava makes steep stratovolcanoes

10. Volcanism releases gases from the interior into the atmosphere (Outgassing).

11. Tectonics
Convection Cells- in the mantle creates stresses in the crust

12. Erosion
Erosion can wear away existing rock and create new features by depositing debris

13. Factors that affect geologic processes

14. Erosion Requires an atmosphere!
Erosion -weather driven process, breaks down or transport rock
Caused by
Glaciers
Rivers
Wind
Requires an atmosphere!

15. Planetary Magnetic Fields protect atmospheres:
Created by charged particles moving inside
3 requirements:
Molten interior
Convection
Moderately rapid rotation

16. What causes geologic activity?
Geologically active planets have a molten interior.

17. How planets heat up: Accretion Differentiation Radioactive decay
These processes
important in the past.
Accretion
Differentiation
Radioactive decay
This process is the most important heat
source today.

18. How the interior cools down:
Radiation: transfer of heat by electromagnetic waves (here infrared).
Condution: Heat transfer as a result of direct contact.
Convection: Heat transfer by means of hot material expanding and rising and cool material contracting and sinking.
Convection cell: small region of rising & falling material.

19. Role of Planetary Size
Smaller worlds cool off faster and harden earlier
Larger worlds remain warm inside, promoting volcanism and tectonics
Larger worlds also have more erosion because their gravity retains an atmosphere

20. Role of Distance from Sun
Planets close to Sun are too hot for rain, snow, ice and so have less erosion
More difficult for hot planet to retain atmosphere
Planets far from Sun are too cold for rain, limiting erosion
Planets with liquid water have most erosion

21. Role of Rotation
Planets with slower rotation have less weather and less erosion and a weak magnetic field
Planets with faster rotation have more weather and more erosion and a stronger magnetic field

22. Geologic processes that shaped Mercury.

23. Cratering of Mercury
A mixture of heavily cratered and smooth regions like the Moon
Smooth regions are likely ancient lava flows

24. Cratering of Mercury Caloris basin is largest impact crater on Mercury
Region opposite Caloris Basin is jumbled from seismic energy of impact

25. Tectonics on Mercury
Long cliffs (scarps) indicate that Mercury shrank early in its history
As much as 3 km high and 20 to 500 km long
Not produced by plate tectonics

26. Mercury has a big core
Ancient impact with a large body may have stripped off mantle material.

27. Major geological features of Venus
The surface is flat, only a few major highlands
Its size means Venus should still be hot inside, but no long mountain chains.

28. Cratering on Venus Impact craters, but fewer than Moon, Mercury, Mars
Small number of craters indicates that surface is young.

29. Volcanoes on Venus
Many volcanoes, including both shield volcanoes and stratovolcanoes

30. Tectonics on Venus
Fractured and contorted surface indicates tectonic stresses

31. Erosion on Venus
Photos of rocks taken by lander show little erosion

32. Venus 'surface seems to have been “repaved” 750 million years ago
Strong convection prevents the formation of thick crust
Crust undergoes wrinkling and flaking.

33. Major geological features of Mars

34. Cratering on Mars
Surface in the south is heavily cratered, indicates an old surface.
Surface in the north is smooth, indicates relatively young surface & geologic activity.
Southern highlands 5 km higher than northern lowlands

35. Volcanism on Mars Mars has many large shield volcanoes
Olympus Mons is largest volcano in solar system

36. Tectonics on Mars
System of valleys known as Valles Marineris thought to originate from tectonics

37. Evidence of Water on Mars
No liquid water or rainfall on the planet’s surface today
However, liquid water once flowed on Mars, as evident in many surface features
Riverbed
“Island” carved by flash flood

38. Martian Rocks
Mars rovers have found rocks that appear to have formed in water

39. What geological processes shaped our Moon?

40. Cratering of Moon
Some areas of Moon are more heavily cratered than others

41. Lunar Maria
Smooth, dark lunar maria are less heavily cratered than lunar highlands

42. Formation of Lunar Maria
Early surface covered with craters
Large impact crater weakens crust
Heat build-up allows lava to well up to surface
Cooled lava is smoother and darker than surroundings

43. Tectonic Features
Wrinkles arise from cooling and contraction of lava flood

44. How is Earth’s surface shaped by plate tectonics?

45. Mantle material erupts where seafloor spreads
Seafloor is recycled through a process known as subduction

46. Thin seafloor crust differs from thick continental crust
Dating of seafloor shows it is usually quite young

47. Major geological features of North America record history of plate tectonics

48. Himalayas are forming from a collision between plates

49. Red Sea is forming where plates are pulling apart

50. Rifts, Faults, Earthquakes
San Andreas fault in California is a plate boundary
Motion of plates causes earthquakes

51. Volcanism & Erosion
Continually renew the surface & erase the evidence of impact craters.

52. Hot Spots
Hawaiian islands have formed where plate is moving over volcanic hot spot

53. Erosion by Water
Colorado River continues to carve Grand Canyon

54. Erosion by Ice
Glaciers carved the Yosemite Valley

55. Erosion by Wind
Wind wears away rock and builds up sand dunes