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Ron Baalke wrote:
Green mineral indicates red planet is dry Just like Utah? Where can someone get a beer around here? :-) |
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In article ,
says... This area is only 30,000 sq. kilometers or comparable to an area of 300km by 100km. Saying Mars is dry on the basis of this is like saying Earth is dry on the basis of the Sahara desert. An earlier report measuring olivine over large parts of Mars found olivine on 1 million square miles: New Evidence Suggests Cold, Dry Mars posted: 07:18 am ET 02 November 2000 http://www.space.com/scienceastronom...ry_001101.html This report also claimed Mars has always been dry on this basis. The problem is that Mars with a diameter of about 4000 miles means 1 million square miles corresponds to about 2% of the Martian surface, using the formula for surface area for a sphere 4*Pi*radius^2 and 2000 miles for the radius. But Earth itself has desert areas that account for 20% of its land area, and even when you account for the fact that the Earth is covered by 70% water, that means deserts on Earth account for 6% of its total surface area: Desert Habitats Deserts of the World "Deserts cover about one fifth (20 percent) of the earth's land area. The desert is a harsh environment with very little rainfall and extreme temperatures. " http://www.enchantedlearning.com/bio...t/desert.shtml So saying saying Mars is dry by looking at the portion that contained olivine ignoring the overwheling majority that did not is like looking at only the desert areas on Earth and concluding that it is dry, and ignoring the wet areas. There is a green beach in Hawaii made of olivine. Not exactly dry there! See: http://www.sease.com/regina/hawaiibeaches.html#green |
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In article ,
Marc 182 wrote: There is a green beach in Hawaii made of olivine. Not exactly dry there! The issue is not that olivine explodes in contact with water :-), but that it's *relatively* reactive in the presence of water, and does not last long *by geological time standards* in a wet environment. That Hawaiian beach is geologically very young (as is everything on the Big Island). There is also at least one greenish beach in the Galapagos, although the green isn't as conspicuous. (Don't know if it's in the guidebooks, but a good guide will point out the green grains in the sand.) Same story -- olivine eroded out of lava. And again, geologically very new. So a big, old area of exposed olivine indicates that at least one part of Mars has been quite dry for a long time. See: http://www.sease.com/regina/hawaiibeaches.html#green The beach is actually sort of olive-drab, not bright green. (And it's not a six-mile hike, unless you're figuring the round trip; it's about three. Mind you, that's three miles out and then three back with no shade and no water except what you brought with you, and it's hot...) -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
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![]() "Marc 182" wrote in message t... In article , says... This area is only 30,000 sq. kilometers or comparable to an area of 300km by 100km. Saying Mars is dry on the basis of this is like saying Earth is dry on the basis of the Sahara desert. An earlier report measuring olivine over large parts of Mars found olivine on 1 million square miles: New Evidence Suggests Cold, Dry Mars posted: 07:18 am ET 02 November 2000 http://www.space.com/scienceastronom...ry_001101.html This report also claimed Mars has always been dry on this basis. The problem is that Mars with a diameter of about 4000 miles means 1 million square miles corresponds to about 2% of the Martian surface, using the formula for surface area for a sphere 4*Pi*radius^2 and 2000 miles for the radius. But Earth itself has desert areas that account for 20% of its land area, and even when you account for the fact that the Earth is covered by 70% water, that means deserts on Earth account for 6% of its total surface area: Desert Habitats Deserts of the World "Deserts cover about one fifth (20 percent) of the earth's land area. The desert is a harsh environment with very little rainfall and extreme temperatures. " http://www.enchantedlearning.com/bio...t/desert.shtml So saying saying Mars is dry by looking at the portion that contained olivine ignoring the overwheling majority that did not is like looking at only the desert areas on Earth and concluding that it is dry, and ignoring the wet areas. There is a green beach in Hawaii made of olivine. Not exactly dry there! See: http://www.sease.com/regina/hawaiibeaches.html#green The problem there is age. If the olivine on Mars is as old as they say it is (billions of years), then, you wouldn't expect to find much olivine left if chemical weathering had occurred. The beaches in Hawaii are much younger, on the order of hundreds of thousands to a few million years, and so are still relatively fresh.. |
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In article , says...
In article , Marc 182 wrote: There is a green beach in Hawaii made of olivine. Not exactly dry there! The issue is not that olivine explodes in contact with water :-), but that it's *relatively* reactive in the presence of water, and does not last long *by geological time standards* in a wet environment. That Hawaiian beach is geologically very young (as is everything on the Big Island). Yeah, I know. The reason I'm aware of that beach is because a geologist coworker returned from his honeymoon waving a vial of green sand around. When I failed to react with the proper shock and awe, the nature of olivine was explained to me in detail... *sigh*. There is also at least one greenish beach in the Galapagos, although the green isn't as conspicuous. (Don't know if it's in the guidebooks, but a good guide will point out the green grains in the sand.) Same story -- olivine eroded out of lava. And again, geologically very new. So a big, old area of exposed olivine indicates that at least one part of Mars has been quite dry for a long time. I didn't really have a point to my post, just being a bit snide. Following up on that theme, "the surface of Mars is dry, wow, never would have expected that!" I do wonder, could this large area of olivine be a dusting of powder eroded by wind and sand from some local volcanic rock (a dusty analog to that beach)? Actually, now that I think about it, the source wouldn't have to be local. Over millennia winds could have selectively sorted out olivine grains in that area. Also, does the presence of olivine rule out permafrost, or other sequestered water, right below it? See: http://www.sease.com/regina/hawaiibeaches.html#green The beach is actually sort of olive-drab, not bright green. (And it's not a six-mile hike, unless you're figuring the round trip; it's about three. Mind you, that's three miles out and then three back with no shade and no water except what you brought with you, and it's hot...) The stuff I saw in that vial was rather pretty, maybe not emerald, but not olive either. The difference between wet and dry sand maybe? Marc |
#8
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"george" wrote in message . ..
"Marc 182" wrote in message t... In article , says... This area is only 30,000 sq. kilometers or comparable to an area of 300km by 100km. Saying Mars is dry on the basis of this is like saying Earth is dry on the basis of the Sahara desert. An earlier report measuring olivine over large parts of Mars found olivine on 1 million square miles: New Evidence Suggests Cold, Dry Mars posted: 07:18 am ET 02 November 2000 http://www.space.com/scienceastronom...ry_001101.html This report also claimed Mars has always been dry on this basis. The problem is that Mars with a diameter of about 4000 miles means 1 million square miles corresponds to about 2% of the Martian surface, using the formula for surface area for a sphere 4*Pi*radius^2 and 2000 miles for the radius. But Earth itself has desert areas that account for 20% of its land area, and even when you account for the fact that the Earth is covered by 70% water, that means deserts on Earth account for 6% of its total surface area: Desert Habitats Deserts of the World "Deserts cover about one fifth (20 percent) of the earth's land area. The desert is a harsh environment with very little rainfall and extreme temperatures. " http://www.enchantedlearning.com/bio...t/desert.shtml So saying saying Mars is dry by looking at the portion that contained olivine ignoring the overwheling majority that did not is like looking at only the desert areas on Earth and concluding that it is dry, and ignoring the wet areas. There is a green beach in Hawaii made of olivine. Not exactly dry there! See: http://www.sease.com/regina/hawaiibeaches.html#green The problem there is age. If the olivine on Mars is as old as they say it is (billions of years), then, you wouldn't expect to find much olivine left if chemical weathering had occurred. The beaches in Hawaii are much younger, on the order of hundreds of thousands to a few million years, and so are still relatively fresh.. Here's another way of presenting the same data: "98% of Mars may have been wet recently". Bob Clark |
#9
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![]() "Robert Clark" wrote in message om... "george" wrote in message . .. "Marc 182" wrote in message t... In article , says... This area is only 30,000 sq. kilometers or comparable to an area of 300km by 100km. Saying Mars is dry on the basis of this is like saying Earth is dry on the basis of the Sahara desert. An earlier report measuring olivine over large parts of Mars found olivine on 1 million square miles: New Evidence Suggests Cold, Dry Mars posted: 07:18 am ET 02 November 2000 http://www.space.com/scienceastronom...ry_001101.html This report also claimed Mars has always been dry on this basis. The problem is that Mars with a diameter of about 4000 miles means 1 million square miles corresponds to about 2% of the Martian surface, using the formula for surface area for a sphere 4*Pi*radius^2 and 2000 miles for the radius. But Earth itself has desert areas that account for 20% of its land area, and even when you account for the fact that the Earth is covered by 70% water, that means deserts on Earth account for 6% of its total surface area: Desert Habitats Deserts of the World "Deserts cover about one fifth (20 percent) of the earth's land area. The desert is a harsh environment with very little rainfall and extreme temperatures. " http://www.enchantedlearning.com/bio...t/desert.shtml So saying saying Mars is dry by looking at the portion that contained olivine ignoring the overwheling majority that did not is like looking at only the desert areas on Earth and concluding that it is dry, and ignoring the wet areas. There is a green beach in Hawaii made of olivine. Not exactly dry there! See: http://www.sease.com/regina/hawaiibeaches.html#green The problem there is age. If the olivine on Mars is as old as they say it is (billions of years), then, you wouldn't expect to find much olivine left if chemical weathering had occurred. The beaches in Hawaii are much younger, on the order of hundreds of thousands to a few million years, and so are still relatively fresh.. Here's another way of presenting the same data: "98% of Mars may have been wet recently". Bob Clark That also assumes that all of the olivine on mars that is going to be found has been found. But I understand what you are saying. I think the evidence overwhelming favors the fact that there is still H20 on Mars. The only question for me is was it ever in the right form or abundance that could have produced, or is currently producing life? I think that given what we know today about Mars, the likelihood of that being the case is very good. Will we ever find it? I think its going to be a hard search. |
#10
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In article ,
Marc 182 wrote: So a big, old area of exposed olivine indicates that at least one part of Mars has been quite dry for a long time. ...I do wonder, could this large area of olivine be a dusting of powder eroded by wind and sand from some local volcanic rock (a dusty analog to that beach)? I wouldn't expect it to stay confined to a local area; the Martian winds seem to be quite effective, over long periods, at moving dust around. But probably nothing short of a field geologist on the surface could *completely* rule that out. Also, does the presence of olivine rule out permafrost, or other sequestered water, right below it? Depends on how that water got there, I think, but it seems like it would take careful contriving to make an explanation work over a large area. The beach is actually sort of olive-drab, not bright green... The stuff I saw in that vial was rather pretty, maybe not emerald, but not olive either. The difference between wet and dry sand maybe? I remember it as being olive-drab pretty much everywhere (you see some of it on the ground well before you reach the beach itself). But we couldn't stay long and I can't claim that we really surveyed the area thoroughly; he may have found a particularly nice-looking vein to sample. -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
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