Download Physics 127 Descriptive Astronomy Homework #11 Key (Website

Physics 127 Descriptive Astronomy
Homework #11 Key (Website)
Winter 2015
B-1. Why is the earth geologically active while the moon is not?
The earth is geologically active while the moon is not because the earth has a very hot core which is cooling by driving
convective currents in its mantle while the moon is cooler in its interior and is not cooling by convection. This
difference is primarily a consequence of the earth’s greater mass and size which prevents the earth from cooling in its
interior nearly to the extent that the moon has.
B-2. Rocks found on the moon are between 3.1 and 4.47 billion years old. By contrast, the majority
of the earth's surface is made of oceanic crust that is less than 200 million years old, and the
very oldest earth rocks are about 4 billion years old. If the earth and moon are essentially the
same age, why is there such a disparity in the ages of rocks on the two worlds?
The surface of the earth is constantly being worn down by erosion, mostly a consequence of water flow on the surface
and wind, neither of which are factors on the moon’s surface. Furthermore plate tectonics is responsible for constantly
reforming and repaving the earth’s surface. This also does not happen on the moon.
B-3. Why do most scientists favor the collisional ejection theory of the moon's formation?
This theory is entirely consistent with current models for the solar system’s formation and also explains why the moon
is nearly in the ecliptic plane rather than the earth’s equatorial plane which is the case with other large moons and their
planets in the solar system.
B-4. Temperature variations between day and night are much more severe on the Moon than on
Earth. Explain why.
The moon has no atmosphere. On the earth the atmosphere acts as an insulating blanket and also its mixing in wind
flow mixes warmer and colder air masses tending to even out the temperature on the earth’s surface which further
reduces the daily temperature swings. Finally, the widespread presence of water on the earth, which is very slow to
warm and cool tends to minimize temperature fluctuations on earth.