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Brady Yoon
2004-May-16, 05:35 AM
Is it possible that the atmosphere of Venus was formed by a recent giant asteroid impact that caused massive volcanoes to release carbon dioxide into the air? Maybe Venus could have been habitable before this. In this article, it says that a masive asteroid impact, on the order of lets say 100 km or larger, could boil off all the oceans, and the higher temperatures would cause the water vapor to escape, and the CO2 and nitrogen would be left behind. This might belong in the "Against the Mainstream" forum.



Thanks,
Brady Yoon.

http://www.xs4all.nl/~carlkop/safemars.html

The Supreme Canuck
2004-May-16, 05:45 AM
Well, such a large impact would leave a rather large crater. Now, from my (not too extensive) knowledge of Venus, there isn't such a crater and so there is no evidence of this occurring. Now this doesn't mean that it isn't a possible occurance elsewhere, just that it doesn't appear to have happened on Venus.

Brady Yoon
2004-May-16, 05:57 AM
Well, such a large impact would leave a rather large crater. Now, from my (not too extensive) knowledge of Venus, there isn't such a crater and so there is no evidence of this occurring. Now this doesn't mean that it isn't a possible occurance elsewhere, just that it doesn't appear to have happened on Venus

Then is it possible that the impact caused the volcanism and global melting that occurred 600 million years ago?

Scenario:
Billions of years ago after the Heavy Bombardment Period: Venus was a haven for life, because the sun was much dimmer at that time.

600 million years ago: A giant asteroid, maybe the size of Ceres today, hit Venus, causing the entire surface to melt, causing catastrophic volcanism, boiling any oceans, and exterminating all life.

This would erase any crater and it could have triggered or reinforced a greenhouse effect. Is there any evidence that this could have happened, or is it speculation?

The Supreme Canuck
2004-May-16, 06:03 AM
Again, I'm not an expert on Venus, but I haven't seen any evidence of this. That doesn't discount it, mind you, but it's still speculation. Given that Venus is volcanically active, it may be difficult to find the crater, but it should still be there.

Brady Yoon
2004-May-16, 06:07 AM
Thanks for the replies. I guess the mainstream theory still works best. :D

The Supreme Canuck
2004-May-16, 06:15 AM
No problem.

By the way, what is the mainstream theory?

Brady Yoon
2004-May-16, 06:24 AM
The gradual increase in the sun's luminosity in the main sequence stage created a runaway greenhouse effect. It says that there's no catastrophe involved; a gradual, inevitable process.

The Supreme Canuck
2004-May-16, 06:26 AM
Ah, thanks. I had no idea. Like I said, not an expert on Venus. :)

Brady Yoon
2004-May-16, 06:29 AM
It says that the temperature of Venus, when it formed, never grew cool enough for the water vapor in the atmosphere to condense. Therefore, the water vapor remained in the air, plus the carbon dioxide. On Earth, the water vapor condensed and it rained for many millenia, cooling the surface and dissolving the carbon dioxide in the oceans and carbonate rocks. Because the essential greenhouse gases remained in the atmosphere in Venus, a runaway greenhouse effect began. Clouds formed from water vapor partially offsetted the rise in temperature, but that could go on only for a short time. Soon, the water vapor was separated into hydrogen and oxygen, and the lighter hydrogen escaped, and the oxygen reacted with other elements. Now, Venus is a dry world with an atmosphere of mainly carbon dioxide and nitrogen formed from volcanic eruptions.

Whew, that's long. Long story short, Venus was predestined to be doomed, because the temperature didn't cool to the condensing point of water early in its history.

Brady Yoon
2004-May-16, 06:30 AM
Oops, I think the first post was only part of it. #-o

Emspak
2004-May-17, 04:22 PM
If it helps any, David Grinspoon writes in Venus Revealed that as the temperature of Venus built up, the surface rocks had all their water boiled away, and became rather stiff and immobile, unlike the rocks on Earth. Water functions as sort of a huge lubricant -- it helps the rocks on Earth slide past each other, to say nothing of making them more flexible. So Earth has plate tectonics, with some plates running under each other and zones of sea-floor spreading where crust comes up. That helps get rid of heat.

Venus doesn't have any rocks that can get under any others-- they are all equally light and dry, with no flex to slide under and over each other. SO the heat builds up. And builds, and you get periods of catastrophic vulcanism that rework the surface completely. So the result is Venusian geology (or Aphroditeology, I guess) is dominated by hot spots.

Yep, that water... important stuff.