Lesson 13

SURFACE FEATURES

I. Geologic and Atmospheric Processes:

1.A variety of planetary processes occur on Earth, including wind and water erosion, tectonics, volcanism, and impact cratering.

2. Weathering encompasses all the processes that cause rocks to fragment, crack, crumble, or decay.

a. These processes can be physical such as freezing water can cause rocks to crack.

b. Or they can be chemical such as decaying of minerals in water or acids.

c. Finally, they can be biological such as plant roots widening cracks or rocks.

3. The rock debris caused by weathering then can be loosened and carried away by erosional agents.

a. Running water such as fast flowing rivers, rain, and ocean waves.

b. High-speed winds that feel like sandblasting.

c. Ice such as glaciers.

4. Landslides occur when masses of rock or debris move down a slope.

II. An Atmosphere’s Effect of Weathering:

1.Whether a planet has an atmosphere depends on many things, including its mass and gravitational field.

a. A strong gravitational field retains an atmosphere.

b. Low gravitational field allows planet’s atmosphere to escape.

2. Mercury has too little gravity.

3. The Moon has too little gravity.

4. Both Mercury and the Moon have been geologically dead for nearly 3 billions years because there is no atmosphere.

5. With no atmosphere there can be no weathering.

6. However, because there is no atmosphere meteorites and other small particles can penetrate and impact the surface with craters. This is a source of weathering.

a. These meteorites break up into rocks.

b. These rock fragments are thrown out and around forming regolith, which is loose unconsolidated material that makes up the surface of a planet or moon.

c. Unlike Earth, regolith does not contain humus, the organic remains of decomposed vegetation.

d. The older the planetary surface the thicker the regolith.

7. Winds are possible only on planets that have atmosphere.

a. Thinner atmosphere (less dense) have faster winds.

b. Wind erosion occurs when gas molecules bounce against rocks and other surface features.

c. Thinner air means fewer molecules, which means you need faster winds to do the same amount of work as a denser atmosphere could do in the same amount of time.

d. Mars’ atmosphere is very thin. It takes a lot of wind to move a regolith.

e. Venus’ atmosphere is very thick (or dense) and it takes very little wind to move a regolith.

8. Unlike Mercury and the Moon, Venus, Mars, and Earth have retained their atmosphere, and the presence of an atmosphere means the possible presence of water.

a. Distance from the Sun and planet size helps to determine water potential

b. Mars had a thick atmosphere early in its history and had liquid water. This changed with the absence of CO2 (a greenhouse gas) and the temperature dropped and water eventually froze.

c. Venus had a reverse effect where there was extreme greenhouse effect which led to a permanent loss of water.

9. Tectonics refers to the forces or conditions within a planet or moon that cause movements in the crust and/or compression of the crust.

10.Plate tectonics, in which the curst responds to internal forces dividing the outer area into plates that move relative to each other is shown on Earth but not on Mars or Mercury.

a. Mercury has distinctive long lines of cliffs formed by the faulting or fracturing of its crust.

b. After craters were formed, the planet shrank forming a wrinkled crust.

c. Mars has a most spectacular tectonic feature, a canyon system, called Valles Marineras. It expands 4000 kilometers, nearly a quarter around the plane!

11. Venus has an active geology that includes both tectonics and volcanism.

a. There is no water or ice on Venus.

b. Surface winds are very low.

c. About 80% of the surface consists of lowland lava plains called maria.

12. The Moon remained volcanically active for about a billion years after the formation of the large impact craters.

a. about 17% of the surface is covered with young volcanic plains

b. Mercury’s surface is similar to the Moon’s surface.

13. About a dozen very large volcanoes have been found on Mars.

a. They are similar in shape to Earth’s volcanoes on Hawaii and Galapagos Islands.

b. This means that they formed from overlapping flows of ‘runny’ basaltic lava.

c. Olympus Mons, the volcanic Martian mountain, has very few impact craters.

14. To assist you in investigating surface features a stream table, make of a waterproof box with a plastic insert and drain hole will represent such concepts as regoliths.