1. Earth data: Average distance from Sun = 1.5 x 10⁸ km = 1 AU

Orbital period = 365.256 days

Rotational period = 23 hours 56 minutes

Diameter = 12,756 km

Average density = 5.5 x water= s density

Average temperature = 14 ^oC (day and night)

2. The fraction of incoming sunlight that a planet reflects is called its albedo. Earth= s albedo is 0.31. The other 69% of the sunlight is absorbed by Earth= s surface and re-emitted as infrared radiation. Most of the infrared radiation escapes back into space, but some of it is trapped by certain gases in Earth= s atmosphere. The trapped radiation heats both the atmosphere and the surface. This extra heating is called the Greenhouse Effect. Without any Greenhouse Effect, all of the water on Earth would be frozen. If the greenhouse gases (mainly carbon dioxide and water vapor) keep rising, all of the ice on Earth will melt.

3. Earthquakes produce seismic waves that travel through the interior of the Earth. The study of these waves reveals that the Earth has a small, solid inner core made of a single crystal of pure iron, surrounded by a molten outer core also made of iron with a bit of nickel. Above this lies the mantle, which is solid except for the uppermost few hundred kilometers, which is "plastic." This thin plastic layer is slowly moving due to convection (hotter material rising, and cooler material falling). At the surface is a very thin low-density crust. (The crust is up to 5 km thick under the oceans and up to 35 km thick beneath the continents.) Earth= s crustal plates move along with the plastic mantle, causing the motion of the continents called continental drift.

4. Radiation belts are made of electrically charged particles (protons and electrons from the solar wind) that are trapped in a planet's magnetic field. On Earth, these two belts are called Van Allen radiation belts. The inner belt contains mostly protons and the outer belt contains mostly electrons. Some of these charged particles may strike oxygen and nitrogen molecules in our atmosphere, causing them to glow. This is called an aurora.

5. The protosun= s violent T Tauri wind stripped Earth of its original atmosphere. Earth's atmosphere was renewed by the outgassing of volcanoes, so the atmosphere consisted mostly of water vapor, along with some carbon dioxide and sulfur dioxide. Today, nitrogen and oxygen make up most of the Earth's atmosphere. About 78% of the molecules in our atmosphere are nitrogen, and 21% of the molecules are oxygen. The nitrogen/oxygen (circle one) is released by plants through photosynthesis. Some nitrogen/oxygen (circle one) was originally released by volcanoes, but there is also some from the decay of all types of organic material. Large amounts of nitrogen/oxygen (circle one) in a planet's atmosphere can arise only through the presence of life. Life has not arisen on other planets in our solar system (as far aw we know), so their atmospheres do not contain any nitrogen/oxygen (circle one). And although nitrogen/oxygen (circle one) is present in some planets' atmospheres, it is of volcanic, and not biological, origin.

6. Much of the Moon= s near side, and nearly all of its far side, are covered by impact craters. The Moon has no atmosphere and no liquid water on its surface, so the craters have not been eroded by wind or flowing water since they were formed. Geological activity such as plate tectonics is the only other mechanism that can obliterate craters, but the Moon is a small world. Its interior has cooled off so the Moon has no geologic activity to remove its craters.

7. The Moon does not have a global magnetic field. The study of moonquakes has revealed that the Moon has a small iron-rich core. Its low-density crust is about 60 km thick on the near/far (circle one) side, and 100 km thick on the near/far (circle one) side. The Moon= s interior is more solid than Earth= s, indicating that the Moon has cooled off slower/faster (circle one) than Earth has. This is because the Moon is smaller/larger (circle one) than Earth. In general, the smaller/larger (circle one) the world, the less internal heat it is likely to have retained. Because the Moon rotates slowly and has does not have a molten interior, it does not have a magnetic field.

8. The Moon's gravity causes tides in Earth's oceans. The force of gravity between two objects is larger/smaller (circle one) when the two objects are closer together. On the side of Earth facing the Moon, the ocean is closer to the Moon than the sea floor is. The Moon's gravity pulls more strongly on the ocean than it does on the sea floor. The ocean is pulled away from above the sea floor, thus producing a high tide. On the side of Earth away from the Moon, the sea floor is closer to the Moon than the ocean is. The Moon's gravity pulls more strongly on the sea floor than it does on the ocean. The sea floor is pulled away from below the ocean, thus producing another high tide. Earth= s gravity also causes tides in the Moon= s crust. The force of Earth= s gravity on the Moon= s tidal bulge caused and maintains the synchronous rotation that keeps the same side of the Moon always facing Earth.

9. According to the Collisional Ejection Theory of the Moon= s origin, Earth was hit by a very large (about Mars= size) object when Earth was quite young. This impact caused the ejection of material from Earth which eventually coalesced to form the Moon. Because Earth was already chemically differentiated (the heavy iron had already sunk to Earth= s core) when this large impact happened, iron is much less/more (circle one) abundant on the Moon than it is on Earth.

10. Like Earth, the Moon is about 4.6 billion years old. However, the lunar maria (Aseas@) are relatively recent features. They were formed after a time of violent impacts with massive asteroid-size objects which lasted from about 4.6 billion years ago to 3.8 billion years ago. The force of these impacts cracked the Moon= s thin crust. Volcanism began about 3.8 billion years ago, when molten lava began to flow out from the Moon's interior. These lava flows lasted until about 3.1 billion years ago. By then the lava had covered the many craters that were on the surface at that time. Because few craters have been formed since then, there are relatively few craters in the lunar maria.

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