Earth is unique in the solar system, so we'd better start
taking care of it!
Earth is clearly a dynamic world with an active atmosphere
and lots of water!
Most scientists stilll feel that for life to exist, you
need water — and Earth has plenty of it! While it's
true that Mars, our Moon, and some satellites of the outer
planets may have frozen water, Earth is the only place that
has surface water in solid, liquid, and gaseous forms.
Liquid water is especially important because it helps to
buffer temperature changes on the planet. Earth's average
surface temperature is about 7° C. This may be rising,
due to changes in the composition of our atmosphere.
Unlike Venus, where the atmosphere is mostly CO2, Earth's atmosphere is about 78 percent nitrogen, 21 percent oxygen, and less than one percent carbon dioxide. Recent satellite and high altitude balloon data provided by NASA show that concentrations of this greenhouse gas (CO2) are on the rise, as are surface temperatures.
If these current trends continue, within 100 years, the average global surface temperature might rise 1–2° C. This may not sound like much, but it could have serious effects on climate, sea level, weather patterns, and our ability to produce food.
Earth is unique in one more way — it's tectonically
active. The surface is in constant motion, with erupting
volcanoes and earthquakes common-place events. While there
is evidence that Venus also has erupting volcanoes, and
Mars was active in the past, plate tectonics here on Earth
are alive and well, and show no sign of slowing down!
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