I was checking out this artical on CNN.com (a bastion of good science) which suggest that the huge canyon on Mars was caused by asteroids melting ice forming floods.

Isn't the current theory that these canyons were formed by things like plate tectonics, or gradual erosion from a period of time when Mars had water?

Reverend J

I haven't read the CNN report, just the one on yahoo. Neither one has all that good a reputation.

As i understand it, one of the theories gaining a bit of ground (or maybe the proponent is just getting louder) is that Mars never went through a long period of liquid water--that, barring impact events or vulcanism, Mars has always been a cold frozen rock.

I'm not sure how this relates to Valles Marineris (the nineplanets page says that this is not an erosion feature, but more likely stretching and cracking associated with the Tharsis bulge). But, some of the canyons that are thought to be erosion features have some peculiarities (like, the water would seem to have had to run uphill, or they are missing tributaries or exits--that type of thing). Some of these could be explained by other "cold" erosional mechanisms.

Here is the original press release that the news services picked up.

The press release states: "...roughly 25 huge impactors, each about 60 miles to 150 miles in diameter, slammed into Mars roughly every 10 million to 20 million years during the period, blowing a volume of debris equivalent to a global blanket hundreds of yards thick into the atmosphere."

Wouldn't similar impacts occur on Earth at that time?

Thanks for the link. It's amusing to see how it was changed for publication.

Anyway, as to similar impacts occuring on the earth, I don't know. But, Mars is much closer to the asteroid belt; i'd expect more impacts on Mars than on Earth, despite Mars' smaller size and gravity. And erosion is much more active on Earth, which would tend to obliterate much of the evidence.

According to the article, the impacts would have happened about 3.5 billion years ago. This is certainly long enough for evidence of all but the worst terrestrial impacts to have been obliterated.

As far as I know, there is no credible evidence that there was ever tectonic activity on Mars. Certainly the very size of Olympus Mons, and the lack of a volcanic mountain chain, seems to indicate this.


-Adam

The thrust of the piece was that Mars was normally cold and dry. The asteroid/comet impacts brought enough water with them or generated enough heat to unleash the frozen Mars water. The rains would have been very hot and torrential (I almost said "hot and heavy"). The heat generated by the impacts was very short-term probably only a few thousand years, after which things cooled off and dried up again.

Basically, the theory holds out little hope for evidence of ancient life on Mars.

MSNBC's might have been more in depth: http://www.msnbc.com/news/843641.asp?0dm=C23CT

If the thing that hit us and created the Moon happened anywhere but very close to when our planet formed (even then isn't there the possibility that it could have literally ripped our planet apart?), there would still be artifacts of the event visible today. Or perhaps that is why our planet has tectonic plates and Mars does not? -Colt

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Be not afraid of any man no matter what his size; when danger threatens, call on me, and I will equalize.

Well, my astronomy textbook, dated at 2000, states that: "All of the old, solid surfaces in the solar system are heavily cratered by meteorite impacts. Earth's moon, Mercury, Venus, Mars, and most of the moons in the solar system are covered with craters. A few of these craters have been formed recently by the steady rain of meteorites that falls on all the planets in the solar system, but most of the craters we see appear to have been formed roughly 4 billion years ago in what is called the heavy bombardment, as the last of the debris in the solar nebula [the cloud of gas and dust that formed the sun, planets, asteroids, comets of the solar system] was swept up by the planets."

It is believed the solar system began forming about 4.6 billion years ago.

If the "large impact hypothesis" is true (that the moon was formed from a Mars-sized planetesimal smashed into the proto-Earth), it should be noted that the Earth is described as being in its "proto" state at the time (the crust had not yet solidified).

The heavy bombardment occurred after the Earth's crust and the moon, along with the other terrestrial planets and the other moons, had solidified. Because of Earth's geologic activity, as far as I've heard, all ssigns of this activity on Earth have been erased (volcanic activity, earthquakes, tectonic subduction, continental drift, erosion, mountain building).

I don't know if it's been determined why the Earth has the such a high degree of tectonic activity while the other terrestrial planets do not.


_________________
"Once again, we find that science is a two-headed beast. One head is nice, . . . but the other head of science is bad! Oh beware the other head of science, Arthur, it bites!" - The Tick vs. Dinosaur Neil

<font size=-1>[ This Message was edited by: nebularain on 2002-12-06 21:15 ]</font>

^ I know that stuff. [img]/phpBB/images/smiles/icon_smile.gif[/img] I was just rambling and flinging out ideas. [img]/phpBB/images/smiles/icon_biggrin.gif[/img] -Colt

__________________
Be not afraid of any man no matter what his size; when danger threatens, call on me, and I will equalize.