Comments on: Ancient Rock Find Supports Early Date for First Photosynthetic Life http://ecolocalizer.com/2009/08/03/ancient-rock-find-supports-early-date-for-first-photosynthetic-life/ News & commentary on sustainability, activism, urban planning, politics, and our world. Fri, 25 May 2012 16:38:57 +0000 hourly 1 http://wordpress.org/?v=3.3.2 By: Michael Ricciardi http://ecolocalizer.com/2009/08/03/ancient-rock-find-supports-early-date-for-first-photosynthetic-life/comment-page-1/#comment-61639 Michael Ricciardi Wed, 16 Sep 2009 23:35:23 +0000 http://ecoworldly.com/?p=3363#comment-61639 Thank you for the clarification. I altered my phrasing to reflect this. However, that said, the precursor "hydrous iron oxides" that you mention (and which are subsequently "dehydrated") could very well have once resided--prior to their dehydration--in an aqueous environment. The mistake was in not elucidating the more involved chemo-morphological sequence that you note. Another factor in this may be the amount of dissolved Oxygen in said liquid (assuming it to be water). Thank you for the clarification. I altered my phrasing to reflect this. However, that said, the precursor “hydrous iron oxides” that you mention (and which are subsequently “dehydrated”) could very well have once resided–prior to their dehydration–in an aqueous environment. The mistake was in not elucidating the more involved chemo-morphological sequence that you note. Another factor in this may be the amount of dissolved Oxygen in said liquid (assuming it to be water).

]]> By: Kent http://ecolocalizer.com/2009/08/03/ancient-rock-find-supports-early-date-for-first-photosynthetic-life/comment-page-1/#comment-61638 Kent Wed, 05 Aug 2009 14:18:57 +0000 http://ecoworldly.com/?p=3363#comment-61638 "...or perhaps, evidence of abundant surface water (as hematite is typically formed in aqueous conditions)." Typically forms in aqueous conditions? This is an all too common misconception. Hematite (Fe2O3) rarely, if ever, forms directly in "aqueous conditions"... liquid water. It forms as the result of a dehydration of a number of precursor hydrous iron oxides (goethite, ferrihydrite)... the water is gone! Thus, the presence of hematite, especially the "coarse-grained gray hematite" seen from space over broad areas on Mars, means that water was present at some time in the past and the rocks were dehydrated later. Not exactly a beacon in the search for life or even life processes. The hematite found by the Mars rovers was in rocks billions of years old and it's hard enough to find evidence of life on Earth in rocks that old. “…or perhaps, evidence of abundant surface water (as hematite is typically formed in aqueous conditions).”

Typically forms in aqueous conditions? This is an all too common misconception. Hematite (Fe2O3) rarely, if ever, forms directly in “aqueous conditions”… liquid water. It forms as the result of a dehydration of a number of precursor hydrous iron oxides (goethite, ferrihydrite)… the water is gone! Thus, the presence of hematite, especially the “coarse-grained gray hematite” seen from space over broad areas on Mars, means that water was present at some time in the past and the rocks were dehydrated later. Not exactly a beacon in the search for life or even life processes. The hematite found by the Mars rovers was in rocks billions of years old and it’s hard enough to find evidence of life on Earth in rocks that old.

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