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Inyo
Inyo wrote:

Over at
http://www.simonsfoundation.org/quanta/20140424-early-life-in-death-valley/ - 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 to 750
million years ago.



Probably no need to point out the obvious error in geologic age approximation here, but what I meant to say, above, is that ..."microbial communities had already colonized terrestrial habitats some 1.2 billion to 750 million years old.

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Inyo

Over at
http://www.simonsfoundation.org/quanta/20140424-early-life-in-death-valley/ - 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 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 land-life is 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 - 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--possibly geologically
correlative with the Mescal Limestone in Arizona that produces 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).
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