"Could the Meridiani Spherules be Surficial?" |
"Could the Meridiani Spherules be Surficial?" |
Jul 10 2007, 04:37 PM
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Junior Member Group: Members Posts: 42 Joined: 2-July 07 Member No.: 2646 |
I have been reading the response to the reponse to impact-surge linked by Dr Burt in post 170. The MER team objects to the impact-spherule explanation because " The spherules are dispersed nearly uniformly across all strata." I agree that is a valid criticism. It is very much like Dr. Burt's criticism of the MER team's hypothesis, that spherule distributions are not consistent with any conceivable ground-water movement regime that should have controled the development of concretions. I agree strongly with this point of Dr. Burt's as well. Neither theory does a good job of explaining the distribution of the spherules. Also, neither theory does a good job of explaining why the spherules do not apparently disturb the bedding.
There may be a solution in a possibilty that I now raise with some trepidation. I think that there is a chance that the spherules are superficial, and not an integral part of the Meridiani strata at all. This probably sounds crazy to many readers, but before rejecting it outright remember that science is at kind of an impasse on this and could use a new idea. If the spherules are superficial this would explain a number of puzzling observations. The layering at Homeplate and Meridiani is most simply explained by impact-surge. It is elegantly and inescapably explained by impact-surge. The impact-surge authors have also tried to explain the Meridiani spherules as part an impact event. If doubts are raised that the spherules are integral to the deposit, this would not in any way be inconsistent with the impact-surge origin of the layered structure. On the contrary, an objection to impact surge would be removed. I intend to start another thread under Opportunity to discuss this question. The first posting should be mine and should be an organized outline of how it might be possible that the spherules have been mis-interpreted as part of the Meridiani layered deposit. I am working on it. If anyone wants to start in on me with the obvious objections, do it here for now. Maybe Dr. Burt would like to respond. No matter what the details of spherule formation in an impact or spherule deposition in the impact sediments, the very uniform distributions that we see are troublingly unlikely. Random distributions are possible from explosive dispersal but less likely than some kind of clustering because of the rapidly changing conditions in the surge cloud. The more-uniform-than-random distributions of spherules on rock characterised by MER-team analysis cannot be explained by impact surge. |
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Jul 13 2007, 04:29 AM
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Senior Member Group: Members Posts: 3419 Joined: 9-February 04 From: Minneapolis, MN, USA Member No.: 15 |
OK -- here are two points that might possibly lead to further discussion. Here's hoping.
First point: If this hematite didn't form within the rocks, but is low-temperature hematite, then how did it form? Perhaps it formed some distance away from where it is now and was transported to its present location. And since 1) hematite can be produced from olivine-rich lavas and 2) there is a lot of olivine in unaltered Martian lavas, it's conceivable that low-temperature water processes could have formed this hematite -- just not in situ. Second point: I know I've read that hematite, once formed, does not melt. If a hematitic bed of rock (formed in whatever climate and under whatever conditions were conducive to such formation) was struck by an energetic meteor (or even a basin-forming event), that hematitic rock bed wouldn't melt, it would be pulverized. Broken into pieces, smallest (dust-sized grains) nearest the impact point and larger away from the impact. Thus, it would be possible for an impact to distribute hematitic fragments within its ejecta blanket. (However, since the hematite would not melt, it would likely not accrete into spherules out of dust-sized granules within the ejecta cloud/surge. I can't imagine anything other than melting that would form the hard, solid berries we see out of hematitic particles and dust, and as has been said, hematite won't melt and therefore can't be annealed into a single solid mass from pulverized particles. And these berries are strong and erosion-resistant, they don't appear to be hematitic dust bound in some other kind of matrix.) I am not siding with an impact origin for the spherules at this point. I need a lot more convincing before I will go that far. However, I believe there *is* a not-altogether-impossible sequence of events which which would allow for it. For the distribution to be so widespread in this area, multiple large impacts would have had to occurred into hematitic rock beds nearby the area. If the layered sulphates actually were laid down on top of berries as they sat on the surface (a process I just don't see evidence of in the MIs of embedded berries), then it is just possible that repeated impacts over time have excavated hematite, spherized the ejected granules either due to impact stresses or due to extreme erosive conditions within the impact cloud/surge, and covered the surface evenly enough and regularly enough for it to *appear* that they are uniformly distributed throughout the rock. However, it just doesn't look like there are berry "deposition planes" within the rocks that would define the surfaces upon which they were deposited. Unless the putative impacts which distributed the berries (all at different distances and releasing different amounts of energy, thus excavating different amounts of rock and ejecting it different distances) somehow produce unformly-sized spherized pebbles each and every time, which I consider highly improbable, then I'm afraid our friend Occam won't approve. The only thing that would make any sense whatsoever, if the berries are ejecta, is that they were ejected from a basin-forming impact partway across the planet. A single large impact event could create zones of ejecta of similar content and character that are hundreds to thousands of miles in extent, in one dimension or another. But again -- if the berries all came from a single huge impact, how did they get so uniformly distributed through the Meridiani sulphate-rich rock beds? -the other Doug -------------------- “The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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