Over at
http://www.simonsfoundation.org/quanta/20140424-early-life-in-death-valley/ is an article detailing rather recent explorations in the Death Valley National Park region that have produced intriguing evidence to help support the hypothesis that abundant photosynthetic microbial communities had already colonized terrestrial habitats some 1.2 billion to 750 million years ago. Too, additional geochemical and paleontological documentation from different terrestrial deposits approximately 2.2 billion years old (not present in the Death Valley area) suggests that land-living oxygen-producing organisms could have substantially contributed to the great oxygenation event that began approximately 2.3 billion years ago.
Of course, just to provide that proverbial "truth in advertising" qualifier, while many investigators with reluctant resignation now recognize that significant microbial terrestrial life existed in the Proterozoic, not a few earth scientists continue to express a natural skeptical dubiety that conclusive proof of land-life first appears in rocks older than around 600 million years.
But, that dramatically distant terrestrial microbial existence of over 600 million years ago is difficult to disprove with definitive convincingness, because leading proponent Paul Knauth, geochemist-geologist with Arizona State University, interviewed in the article referenced above, not only believes he has the significant carbon isotope signatures from such primordial Precambrian deposits to help support the idea, but also loads of fossil, microscopic photosynthetic organisms secured from thin-sectioned rocks of proved karstic, terrestrial origin, roughly 1.2 to 750 million years ancient, including important collections from the world-famous 750 million-year old Beck Spring Dolomite, Death Valley National Park region, which overlies the cyanobacterial stromatolitic developments present in carbonate exposures of the 1.2 to one billion year-old Crystal Spring Formation.
But that's not the conclusion of the story. Not at all. Not only does Paul Knauth adduce abundant evidence to support pre-600 million-year old microbial land colonization, he also firmly advocates the potentially provocative postulation that animal life on earth originated not in the sea (the traditonal paleobiological opinion, of course), but within terrestrial environs; tantalizing, albeit subjectively compelling evidence supports the existence of multi-cellular animals devouring peacefully co-existing 750-plus million year-old photosynthetic microbial communities, just minding their own business, pumping important quantities of oxygen into earth's ancient atmosphere.
Addendum: See my page over at http://inyo.coffeecup.com/site/dv/stromatolites1.htm for close-ups of two dome-shaped stromatolites I encountered in the Precambrian Crystal Spring Formation, Mojave Desert, California, several years ago (outside the boundaries of Death Valley National Park); they're roughly 1.2 to one billion years old--probably geologically correlative with the Mescal Limestone in Arizona that produces possible 1.2 billion year-old terrestrial microbes (an image of one such critter from the Mescal Limestone is included in the article, referenced at the beginning of this post).
http://www.simonsfoundation.org/quanta/20140424-early-life-in-death-valley/ is an article detailing rather recent explorations in the Death Valley National Park region that have produced intriguing evidence to help support the hypothesis that abundant photosynthetic microbial communities had already colonized terrestrial habitats some 1.2 billion to 750 million years ago. Too, additional geochemical and paleontological documentation from different terrestrial deposits approximately 2.2 billion years old (not present in the Death Valley area) suggests that land-living oxygen-producing organisms could have substantially contributed to the great oxygenation event that began approximately 2.3 billion years ago.
Of course, just to provide that proverbial "truth in advertising" qualifier, while many investigators with reluctant resignation now recognize that significant microbial terrestrial life existed in the Proterozoic, not a few earth scientists continue to express a natural skeptical dubiety that conclusive proof of land-life first appears in rocks older than around 600 million years.
But, that dramatically distant terrestrial microbial existence of over 600 million years ago is difficult to disprove with definitive convincingness, because leading proponent Paul Knauth, geochemist-geologist with Arizona State University, interviewed in the article referenced above, not only believes he has the significant carbon isotope signatures from such primordial Precambrian deposits to help support the idea, but also loads of fossil, microscopic photosynthetic organisms secured from thin-sectioned rocks of proved karstic, terrestrial origin, roughly 1.2 to 750 million years ancient, including important collections from the world-famous 750 million-year old Beck Spring Dolomite, Death Valley National Park region, which overlies the cyanobacterial stromatolitic developments present in carbonate exposures of the 1.2 to one billion year-old Crystal Spring Formation.
But that's not the conclusion of the story. Not at all. Not only does Paul Knauth adduce abundant evidence to support pre-600 million-year old microbial land colonization, he also firmly advocates the potentially provocative postulation that animal life on earth originated not in the sea (the traditonal paleobiological opinion, of course), but within terrestrial environs; tantalizing, albeit subjectively compelling evidence supports the existence of multi-cellular animals devouring peacefully co-existing 750-plus million year-old photosynthetic microbial communities, just minding their own business, pumping important quantities of oxygen into earth's ancient atmosphere.
Addendum: See my page over at http://inyo.coffeecup.com/site/dv/stromatolites1.htm for close-ups of two dome-shaped stromatolites I encountered in the Precambrian Crystal Spring Formation, Mojave Desert, California, several years ago (outside the boundaries of Death Valley National Park); they're roughly 1.2 to one billion years old--probably geologically correlative with the Mescal Limestone in Arizona that produces possible 1.2 billion year-old terrestrial microbes (an image of one such critter from the Mescal Limestone is included in the article, referenced at the beginning of this post).