tag:blogger.com,1999:blog-5517176012861550589.post7939391156095008352..comments2023-06-14T21:50:15.221+10:00Comments on Ediacaran: 2.1 Ga Multicellular Colonial Organisms - Umm, NotChris Nedinhttp://www.blogger.com/profile/06978886926715669724noreply@blogger.comBlogger9125tag:blogger.com,1999:blog-5517176012861550589.post-68553112617349890132012-03-04T12:53:13.915+11:002012-03-04T12:53:13.915+11:00Anonymous,
The structures are concretions. That&#...Anonymous,<br /><br />The structures are concretions. That's pretty much accepted by workers. See for example, Dolf Seilacher's papers on concretions to see very similar structures. The mats would have produced the geochemical environment for sulphide mineralisation to occur and form the concretions. The thinning and fracturing around the edges is common to concretions. The folded structure to some of the concretions is the only unusual element, which can be explained by bacterial mats.Chris Nedinhttps://www.blogger.com/profile/06978886926715669724noreply@blogger.comtag:blogger.com,1999:blog-5517176012861550589.post-78707208892532932232012-03-04T07:21:25.122+11:002012-03-04T07:21:25.122+11:00I am not a paleontologist. Invertebrate marine pa...I am not a paleontologist. Invertebrate marine paleontology was my original major and I got pretty far along before switching majors. (Like you said, "No jobs!") I still keep up with the literature. I am familiar with bacterial mats/biofilms, which have not changed much over time. There are some considerations that you might have overlooked. Taken together, they leave me unconvinced about your argument that the Francevillian fossils are bacterial mats. <br />First, some minor considerations: <br />(A) These fossils have not been found in other formations, but they consistently occur in several horizons within this formation. <br />(B) Their age, although certainly not proof of a multicellular, oxygen-metabolizing organism, is provocative. It occurs during the deposition of banded iron formations. <br />(C) Oxygen levels 2.1 Ga were still low. Any oxygen-consuming multicellular organism at that time would probably have been quite small (1-2 cm max) and thin (a few mm), in order to acquire oxygen through its outer tissues. It might have had peripheral folds to increase surface area for oxygen exchange. This is far from proof, but these fossils fit that concept. <br />- Those are minor considerations. The next items are more important: <br />(D) Their shape, although asymmetrical, is pretty regular and recognizable, so it FITS WITHIN A LOOSE PATTERN. This is unlike bacterial mats, which grow to fill the usable space. <br />(E) Their maximum dimensions are limited. This is true in all of the horizons where they occur. This limited size is also unlike bacterial mats, which can grow to be quite large. <br />(F) A single catastrophic event could preserve a group of bacterial mats that did not have time to grow to a larger size. That would explain a limited size range (7 - 12 mm). But these fossils are preserved in several horizons throughout the formation, yet their sizes consistently fit within the same small range. This indicates that they had a MAXIMUM GROWTH SIZE. That is almost a negation of bacterial mats by itself. <br />(E) In other words, these fossils are too consistently small and too regularly shaped to be bacterial mats. <br />(F) ALSO: Most, but not all, fossils of bacterial mats are two-dimensional. The Francevillian fossils have a measurable thickness of up to 1 cm. Any bacterial mats that achieve that thickness would be much larger horizontally than these fossils. The Francevillian fossils are quite small, horizontally (barely over a cm long), yet they are all three-dimensional. Bacterial mats that size would have been just starting out and, therefore, very thin. <br />(G) Bacterial mats do not thin out rapidly toward their edges. <br />(H) Your excellent photos of bacterial mats show the characteristics that paleontologists look for. These include preserved CO2 gas bubbles, wrinkles, and large tears. None of the photos of the Francevillian fossils, in any web site, show these characteristics. <br />(H) The fact that they appear within different horizons of their formation, but do not occur in other formations, argues strongly against an inorganic origin. These are not pyrite pseudofossils.<br />(I) There is nothing to prevent a pyrite nodule from forming in the center of these fossils. I have found lots of pyritisized fossils that had been modified by nodules/crystals. <br />(J) The whole water escape discussion is a red herring (unrelated to the topic).<br /> Hope this helps the discussion!<br />Paul Combs<br />combsbp@yahoo.comAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-5517176012861550589.post-74794275565847051152010-12-30T20:48:41.202+11:002010-12-30T20:48:41.202+11:00Agree completely with the compression cracking int...Agree completely with the compression cracking interpretation - we've seen similar things abundantly in a deposit with early pyritisation from Wales, e.g.:<br />http://asoldasthehills.org/gallery%20Xrays/xray10Joe and/or Lucyhttps://www.blogger.com/profile/06878334304625015880noreply@blogger.comtag:blogger.com,1999:blog-5517176012861550589.post-21825185795116958692010-07-24T10:49:58.120+10:002010-07-24T10:49:58.120+10:00Looking for international Ediacaran experts.Looking for international Ediacaran experts.DinoDragonhttps://www.blogger.com/profile/01136679346113530963noreply@blogger.comtag:blogger.com,1999:blog-5517176012861550589.post-77032227942421926452010-07-20T10:37:30.590+10:002010-07-20T10:37:30.590+10:00I've been to Yellowstone a couple of times, an...I've been to Yellowstone a couple of times, and I had no idea the bacterial mats were that THICK. So thanks for that, along with the rest of it.<br /><br /> - YetAnotherKevinAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-5517176012861550589.post-28440355215346219702010-07-14T22:39:32.663+10:002010-07-14T22:39:32.663+10:00Regarding the steranes see Summons et al. 2006 fo...Regarding the steranes see <a href="http://rstb.royalsocietypublishing.org/content/361/1470/951.full?sid=9343ecbf-75cf-4910-8dd2-13240e352804" rel="nofollow">Summons et al. 2006</a> for references to more sterane finds, so there are a few about.<br /><br />It is unlikely that the steranes leached into the sediment prior to the modern day, as the section is a tight shale with very limited permeability. Modern contamination is always an issue but these are altered compounds - not pristine - and unlikely to just be hanging around waiting to contaminate samples.<br /><br />If we disregard a eukaryotic origin for the host rock 13C values, then it is possible that the 13C represents planktonic photosynthetic cyanobacteria raining down onto the sea floor (or brought in with storm deposits) or sediment-hosted sulphate reducing bacteria. The specimen 13C could then be chemoautotrophic bacteria left over from the pyritisation process that had been fuelled by the microbial mat biomass.<br /><br />It's a bit fuzzy though as 13C ratios depend in part on the 13C of the food source the greater the 13C enrichment or depletion of the food source, the greater the 13C enrichment or depletion of the final biomass). But the main thing is the host rock 13C is consistently different than the specimen 13C, although they didn't explain how they got a 13C value from what is essentially a lump of pyrite.<br /><br />. . . but 'where the data and conclusions get especially wobbly', is where the fun starts :-)Chris Nedinhttps://www.blogger.com/profile/06978886926715669724noreply@blogger.comtag:blogger.com,1999:blog-5517176012861550589.post-50505488642474021002010-07-14T15:17:55.698+10:002010-07-14T15:17:55.698+10:00When I saw the paper (and the hype around it), som...When I saw the paper (and the hype around it), something seemed odd to me. First off, there's no conclusive evidence for eukaryotes past about 1.2-1.4 Ga, so a multicellular eukaryote at 2.1 would require some hardcore indisputable evidence. But I'm not a paleontologist, so I kept the doubts to myself. It's nice to see that at least one paleontologist finds issues with their analysis =D<br /><br />Now RE the steranes and 13C values... I've heard arguments concerning the easy leeching of steranes into lower layers (eg. Cavalier-Smith 2006 PTRSB): do you have any thoughts on this? Secondly, assuming a scenario of no eukaryotes at 2.1 Ga, just for the sake of argument, what else could have resulted in the observed 13C patterns? <br /><br /><br />Anyway I'm happy to have stumbled across your blog, and will read regularly. I'm fascinated by micropal and precambrian stuff, which is sadly where the data and conclusions get especially wobbly... <br /><br />Cheers,<br />-Psi-Psi Wavefunctionhttps://www.blogger.com/profile/10829712736757471647noreply@blogger.comtag:blogger.com,1999:blog-5517176012861550589.post-11758354177970269532010-07-07T22:22:06.969+10:002010-07-07T22:22:06.969+10:00Can I send you an article related to the Ediacaran...Can I send you an article related to the Ediacaran macro body fossils I found in YunNan, China by email?<br /><br />Timothy Huang, timd_huang@yahoo.comDinoDragonhttps://www.blogger.com/profile/01136679346113530963noreply@blogger.comtag:blogger.com,1999:blog-5517176012861550589.post-11041073634524357912010-07-07T04:26:53.076+10:002010-07-07T04:26:53.076+10:00This is a great analysis - research blogging at it...This is a great analysis - research blogging at its best. Thanks!Chris Rhttps://www.blogger.com/profile/10923865059164569384noreply@blogger.com