Liquids evaporate. We have all noticed this with water,
gasoline, and cleaning fluids.
What happens when liquids evaporate?
eviau2001: You know that when you are up on the top of a high mountain, there is
less atmospheric pressure and water boils at a lower temperature?
eanbug: I know that the different atmospheric pressure would effect the weather.
eviau2001: Yes. At low pressure water will evaporate quickly at lower
temperatures than here.
dyyanbug: which would mean it affects the evolution of life and dealing with
storms, rains, etc. is that what you meant?
eviau2001: Boiling is just very enthusiastic evaporation.
eviau2001: The molecules in water are all jumping around in there. The warmer
the water is, the faster the molecules jump.
eviau2001: Some of them jump right out of the water and into the air!
eviau2001: But the armospheric pressure pushes down on the water so that fewer
molecules can escape.
eviau2001: Reduce the pressure and evaporation will happen faster.
eviau2001: Reduce it a lot and you may not have standing water.
dyyanbug: the atmospheric pressure we have currently isn't so low that the
stmosphere will eventually disappear, do we?
eviau2001: With an atmosphere, the small molecules escape to space. Hydrogen is
a small atom.
eviau2001: Big atoms cannot escape as readily.
eviau2001: The gravity of the planet affects which molecules escape.
eviau2001: how fast the planet spins affects that too.
oscar2465: I will do the changes as soon as possiable
eviau2001: You've heard the news talk about escape velocity?
eviau2001: That is how fast something has to be travelling to escape from the
eviau2001: Baseballs do not escape.
eviau2001: Bullets do not escape.
eviau2001: But space ships do!
eviau2001: A small planet has less gravity than a large one, so the atmosphere
can escape more rapidly.
eviau2001: Mars has only one hundredth of the atmosphere that we have here.
eviau2001: Most of the gases escaped into space.
eviau2001: On earth the oxygen and carbon dioxide will probably never be able to
escape, but if all the hydrogen goes, what will happen to the water?
oscar2465: It will evaporate.
eviau2001: Good. Will it condense into rain?
dyyanbug: it's bigger than hydrogen. It wouldn't escape, right?
dyyanbug: so wouldn't it condense?
oscar2465: yes. only the h2 will become a gas and escape.
eviau2001: We would thin not. Good. But when the water gets high into the
atmosphere, the sunlight causes it to photo disociate.
eviau2001: What is water made of?
dyyanbug: oh, the diassociated hydrogen would escape.
eviau2001: Yes, Oscar, you are right The sunlight splits the hydrogen from the
dyyanbug: and the disasociate oxygen?
eviau2001: "Bye Bye!" says the hydrogen as it flies off into space!
eviau2001: But the oxygen stays behind because it is heavier.
eviau2001: However, oxygen is a very friendly element that will combine with
just about anything.
dyyanbug: ok, got it.
eviau2001: Maybe it will attach itself to rocks.
dyyanbug: if iron is in it, it will rust.
eviau2001: But your planet eventually has no water and so nothing can live
dyyanbug: red rocks, Mars.
eviau2001: Yesm a rusty red planet! Good!
eviau2001: So now we will all be wondering if there is water frozen into ice
under the soil of Mars.
eviau2001: Will there be life there? Nobody knows!
eviau2001: It is so cold on Mars that water can sublime (evaporate directly from
a solid) from ice.
eviau2001: But a lot of the ice is from frozen carbon dioxide, which is a heavy
molecule made of oxygen and carbon.
eviau2001: Heavy for a gas, anyway. Metals are much heavier.
eviau2001: The periodic table shows which molecules are heavy and which are
eviau2001: The light molecules are cooked in the stars, and most of the
molecules necessary for life are light and abundant.
eviau2001: Zinc and lead and gold are heavier and more rare.
Header Viau Steam from hot springs in Yellowstone National Park
1996,1997, 1998, 1999,
2000, 2002, 2003.
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