and Mars travel in neighboring orbits around the sun. All of
them are rocky planets, but only the earth has abundant life.
Only the earth has conditions which
support the presence
of liquid water.
The surface temperatures of these planets
are governed by two factors:
- the amount of energy that they receive from
the sun and
- the composition of their atmospheres.
Venus is closer
to the sun than the earth is. It has a very thick, dense atmosphere,
made up mostly of carbon dioxide. The carbon dioxide acts like
a blanket and keeps the sun's heat trapped on the suface of
Venus. This is called the Greenhouse Effect.
us that the temperature on Venus is about 890 degrees Fahrenheit.
This is 477 degrees Centigrade (or Celsius). At this temperature
lead and tin would be melted. Carbon-based life forms would be
vaporized. Water would boil away.
It is difficult to discover what the surface
of Venus is like. Our earth probes do not survive long in the
heat, and the dense,cloud-filled atmosphere makes it difficult to transmit
information and signals.
would be too cold for life if it had no atmosphere. The atmosphere
holds enough of the sun's heat to make life possible here.
Temperatures on earth
range from a high of perhaps 130 degrees Fahrenheit to about
-90 Fahrenheit. There are places on earth in which it is challenging
for us to stay alive. There are living things in most earth environments,
of comparison, let's say the temperature on earth in Los Angeles
is about 70 degrees Fahrenheit, which is 21 degrees Centigrade.
This is pleasant for carbon-based life forms, though some with
adaptations for cold might feel uncomfortably warm.
Mars is the furthest
rocky planet from the sun. It is a smaller planet than the earth,
and has lost much of its atmosphere. The weaker gravity of Mars
allows more atmospheric molecules to escape into space.
As a result
of Mars' very thin atmosphere, solar heat escapes easily. The
temperature on Mars can be as high as 50 degrees Fahrenheit (10
C) at the equator and as low as -185 degrees Fahrenheit (-120
C) at the poles. Carbon-based life forms could survive at the
warmer temperatures (given oxygen and other necessities) but
the water in our cells freezes at 0 C, and maintaining our body
heat would be challenging in even the warmest areas. We would
have to really focus on staying warm at night and during the
winters. For purposes of comparison let's pick -30 Centigrade
(Celsius) for our temperature on Mars.
Now, let's look at the behavior
of some of our familiar elements here and on nearby planets.
- The melting point is the temperature at which
a solid turns into a liquid.
- When a substance reaches its boiling point
it becomes a gas.
||Melting Point C
||Boiling Point C
||State on Venus
at 477 C
|State on Earth
at 21 C
|State on Mars
at -30 C
As you can see, life as we know it thrives
in a narrow temperature range. It is amazing to think that life
has been here for billions of years -- and during all that time,
there has been liquid water on earth every day.
Mountain photograph from a Corel
CD-ROM : for viewing only, not for downloading.
Header from NASA Earth From Space
1999, 2003.. Elizabeth Anne Viau
and her licensors. All rights reserved. This material
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