The surfaces of the Earth and the Moon are very
different. The surface of the Earth is dynamic because it changes
constantly. This is caused by movement of crust, erosion by water and wind,
and living organisms. Plate tectonics changes the positions of the
continents, reshapes ocean basins, and creates mountain ranges and
The Earth’s atmosphere and abundant liquid water and
ice on its surface causes erosion and reworking of the Earth’s surface.
The wind blows, moving material from place to place. Running water and ice
carve away at rocks and loose material. Through time, these processes act to
flatten the Earth’s surface, wearing away mountains and filling in low
The Earth’s surface is modified by the presence of
life. The activity of life enhances the effects of physical surface
processes. In addition, life has modified the compositions of the atmosphere
and oceans. The combination of these forces means that the Earth’s surface
is very young.
The surface of the Moon changes slowly, because none
of these factors are active. The Moon is essentially "dead"
geologically with little tectonic activity. The Moon lacks an atmosphere,
and the small amount of water that is present is "buried" in the
polar areas. Finally, there is no life on the Moon.
The major factor which does change the Moon’s
surface is the impact of meteoroids, forming craters. Even this process is
very slow today; most of the Moon’s craters, and all of the large ones,
are hundreds of millions to billions of years old. The surface of the Moon
is very old, compared to the Earth.
- Ask the students to think about why the Moon and
the Earth are different. You may want to have students fill in a chart
like the one below.