Re: Age of earth by time of its rotation
- From: Kent Paul Dolan <xanthian@xxxxxxxx>
- Date: Mon, 12 Oct 2009 04:40:43 -0700
Jim wrote:
> Kent Paul Dolan <xanth...@xxxxxxxx> wrote:
> <snip>
>> Asteroid impacts' effects on Earth's rotation
>> would roughly even out over time; geological time
>> is a _long_ time, billions of years, compared to
>> large asteroid impact intervals, tens of
>> thousands of years, (there was a doozy about
>> 12000 or 14000 years ago that turned the North
>> American Great Lakes water outflow from "into the
>> Mississippi" to "into the St. Lawrence estuary")
>> so there would have been a _lot_ of impacts, some
>> to speed the earth, some to slow it, some doing
>> neither.
> Nitpick: There is no need to postulate a bolide
> impact to change the outflow of the proglacial
> Great Lakes, as far as I know - the eastern
> outlets were dammed by ice prior to 14 ka; as the
> icecap terminus retreated several successively
> lower outflow channels were opened. There are
> some really spectacular abandoned channels in the
> ridge south of Syracuse, NY, as well as
> spectacular evidence for seriously big water
> flowing through the Mohawk River valley (Little
> Falls, NY was not so little around 13 ka). The
> final transition to the St. Lawrence outlet
> occurred when the ice dam anchored to the
> Adirondack upland at Ft. Covington gave way.
My source has it that an earthen barrier, rather
than an ice barrier, was what gave way, when the
theretofore functional outlet southward via the
Mississippi was suddenly and effectively blocked
with impact debris, and rising water levels caused
by the lakes' outlet being blocked eventually
connected the lakes to one another, then those
levels continued rising until that caged water
stressed and finally overran the weak point in the
east coast mountain range.
> One reason there are no major outflow landforms
> around Montreal is that at the time isostatic
> subsidence had depressed the crust so far that the
> St. Lawrence valley up as far as Ogdensburg was
> below sea level at the time (there are fossils of
> marine clams in post-glacial sediments near
> Ogdensburg). So there is no need for a bolide -
> just melting did the trick. Further, as far as I
> know there is no evidence for any craters in the
> area (unless you count Manacouagan, but that is
> way, way too old).
And yet there's been an hour long, repeating, show
on one of the science channels, probably the
National Geographic channel [Can you tell I'm not
the one in my household who holds the TV remote?]
covering this whole issue, that I've watched through
at least twice now.
Based on the research that show covers, yes, there's
a fairly huge crater (48 km diameter) at the bottom
of one of the Great Lakes, Huron, and evidence of
smaller, perhaps related ones, elsewhere.
http://findarticles.com/p/articles/mi_m1200/is_n9_v138/ai_9396611/
These Google searches yeild useful results:
lake.huron meteor.crater
lake.ontario meteor.crater
The big one at spoken of the in the science program
has a time signature compatible with the diversion
of the water outlet direction from southward to
eastward, as determined by decoding the age of
Niagra Falls, using, guess what, carbon dating of
fresh water (I'm pretty sure I heard "fresh") clam
shells embedded in the banks of the river below the
falls.
The bolide impact can also be dated by carbon dating
the very widespread layer of ash created when the
heat of the impact set off a massive fire storm in
the surrounding forests. The two dating techniques
give dates in close agreement, AIUI.
There's lots, also, about the still ongoing
isostatic rebound uplift of the once ice-burdened
lands north of the ice age glacier's southernmost
incursions. There's hugely visible evidence of that
tilting of the earth, as on one side of the Great
Lakes, (the south) the shoreline water level is
rising as the land sinks relative to the lakes'
metacenters [presumably themselves partaking in the
uplift, thus the motion has to be described as a
relative one], while on the other side (the north)
established lakeside settlements are now high and
dry, the shoreline made distant, as the land rises.
All that highly visible lakeshore movement with
respect to settlements has happened at maximum just
since the Europeans came to North America and built
those settlements, though it had of course been
ongoing for millennia.
It's a good show, catch it if you can. I'm not going
to pretend I can reproduce all of it accurately from
memory.
xanthian.
.
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