(13) (a) Find in the text examples of (i) a small, simple bowl-shaped crater, 9.13 a - center of picture. (ii) a crater with a central peak, 9.13 b - top right. (iii) a multi-ringed basin,figure 9.12b. (iv) a flooded crater - figure 9.22 c.

(b) The crater Copernicus (yes, as you may have gathered, the lunar craters are mostly named after famous scientists) is spectacular - find it here. How far across the Moon's diameter do the ejecta from Copernicus spread? How far is this in kilometers? OR, look at the Moon and look at the Tycho crater slightly left of center at the bottom. The ejecta from the larger, recent impacts spread for at least a lunar radius - about 3000 km.

(14) (a) From the diagrams, how many years ago were the lunar mare formed? About 3.5 - 3.8 billion years ago.

(b) When was the impact that caused the Copernicus crater (or the Tycho crater)? About 0.3 billion years ago.

(15) (a) Look at the figures earlier in this Session, and in the relevant chapters in your book. List the figures with examples of impact craters for (i) Earth, (ii) Venus and (iii) Mars.
(b) What are the factors that cause fewer craters to be visible on (i) Earth, plate tectonics, volcanism and erosion. The whole surface has been turned over many times. (ii) Venus mainly volcanism (partcularly a bit eruption which resurfaced the planet about 800 million years ago), and (iii) Mars - volcanism again - but less than on Venus or Earth.

(16) Would you describe the following as having high or low viscosity: (a) molasses, high viscosity (b) cooking oil, moderate viscosity (less if heated up, more if put in the fridge) (c) oatmeal, VERY viscous (d) beer - low - the ideal viscosity!

(17) Consider what happens when you heat or cool a liquid. Think about what happens to the viscosity (a) when you heat molasses,becomes less viscous (b) to oil in a car engine when the weather is very cold, becomes more viscous (c) to silly putty if you put it in the freezer for half an hour - becomes VERY viscous.

(18) (a) If you put a chunk of cheese under the broiler what happens to it? First, it melts.

(b) If you leave it there longer - before it burns, it starts to bubble. Where did the gases that are in the bubbles come from? The gases were inside the cheese.

(c) Next, we heat up some soup, gently at first. As the soup heats up, what motions do you see in the soup? You see the soup turning over - convecting.

(d) If you keep heating the soup it begins to bubble and then rise up in the pan, finally overflowing the pan. If we think of this is an analogy of lava - then, is this process analagous to the lava (and the gases inside) expanding or of it contracting as it is heated? It is EXPANDING on being heated.

(19) Look at the photos of volcanoes on Earth, Venus, and Mars and see if you can identify what kind of volcano is shown in each case.
(a) EARTH - picture on left is a lava fountain - this is viscous lava with gas which explodes out of the vent.
(b) VENUS 1, these are very high viscosity eruptions - just 'blisters' pushing up the surface. VENUS 2 - These are low viscosity lavas which flow rapidly and produce relatively low angle volcanos. VENUS 3 - This is a 'blister' which has burst or de-flated - the high viscosity lava which welled up underneath has sunken back down.
(c)MARS 1 - huh? I see no here - no idea what this image was supposed to show! sorry. MARS2. This is the large, shield volcano of Olympus Mons - a very shallow slope shows that the lava which made this volcano was very low viscosity.

(20) (a) Which planet has the highest mountain? Olympus Mons on Mars.

(b) So, which planet do you think has the thickest crust? The idea that you need a thick crust to hold up a large mountain suggests that Mars has the thickest crust.

(21) Look at the faults on various planets and describe if they are due to expansion or shrinking (as far as you can tell) of the planet's crust, or two chunks of crust sliding past each other
(a) Earth - this is the San Andreas fault in California where 2 plates (chunks of crust) are sliding against each other.
(b) Moon - these are cracks in lava inside craters on the Moon which look like they have been formed when the lava cooled, shrank and then cracked (like mud cracking when it dries).
(c) Mercury - this crack is really hard to see - cracks on Mercury are thought to be due to the crust shrinking and cracking as the planet cooled down.
(d) Venus 1, - this is not so easy to tell - but it looks like the crust has been folded and creased - as if the crust was being compressed.

Venus 2, - these cracks are produced around a volcanic feature which first pushed up the crust (expansion) and then when the underlying lava receeded, the crust shrank back down, leaving cracks and creases around the previously upwelled region.

Venus 3 - These are cracks around low-viscosity lava flows - as if the outflowing lava stressed the crust which then cracked under the weight of the lava - this would make the cracks due to expansion.
(e) Mars - this large crack on Mars (Valles Marinares) looks like it was caused by expansion of the crust making the crust open up. But why the crust of Mars suffered such a large expansion is not known.

(22) Look in your book for a discussion of plate tectonics on the Earth. Then look at chapters about the other terrestrial planets.
(a)Can you find evidence of plate tectonics on planets other than Earth? Plate tectonics is the large scale motion of large slabs of the crust moving across the planet, colliding and sinking back down into the mantle. The primary evidence of plate tectonics is long, linear features such as mountain ranges or deep trenches. While there are some fairly large - almost continent-like - structures on Venus, they are not really linear. On Mars, we have the big rift of Valles Marinaris, but there is really no evidence of linear mountain ranges. Earth is the only planet where we can say for sure that there is - or has been - plate tectonics.
(b)What do you conclude about the presence of convection in mantles of planets other than the Earth? If there is no plate tectonics, then we must conclude that on the planets other then Earth the mantle is not convecting vigorously enough to move large regions of the crust about.

(23) (a) List all the geological features you can think of that are caused by erosion. Rivers, canyons, dunes, ....

(b) Which of the 4 terrestrial planets + Moon show evidence of erosion? Looking at the figures for these planets in Chapter 9. Earth, certainly. Mars - we see things which look like river valleys, dunes and features which suggest wind erosion. Venus? Venus certainly has an atmosphere - but no water. We have not found much evidence of erosion on Venus. Some argue that the atmosphere of Venus is not only too dry but the lack of rotation means that the surface winds are not very strong.

(c) What is the main agent of erosion? In which form--vapor, liquid or solid--is it most efficient? Water seems to be the most efficient agent of erosion. While solid water - ice - does erode (think of glaciers), the most efficient form is water - carving out deep canyons.

(d) The images below show the same region of Mars taken at two different times. The image on the right shows the appearance of enormous columns of dust that are believed to be similar to dust devils on Earth--they are formed by warm air rising above the ground and carrying with it dust in vortices. This showcases a secondary agent of erosion--wind--which carries rock-dust / sand and `blasts' rocks, eroding them and making more sand. On which planets might this be a significant form of erosion? Only the planets which have atmospheres - Earth, Venus and Mars. On Venus the winds may be too weak to drive much wind erosion.