Something startling here. It appears that the whole crust shifted
thirty degrees around 120,000,000 years ago. Thus my conjecture
regarding the Pleistocene Nonconformity does have a real precedent in
time in space. The shift was also the correct thirty degrees as was
the one that occurred 13,000 years ago.
Since I have been arguing for the recent shift been deliberate, I
knew that there had to be a precedent to work from in order to
attempt such a stunt. I presumed that it had been closer in time but
this is much better. It clearly asks the right questions and
suggests that it can be done again. We will be reaching those same
conclusions over the next few years.
I have also proposed in this blog a plausible alternative explanation
for crustal magnetism that conforms nicely to the available evidence.
The explanation presented here flies in the face of all the evidence
and is mostly hand waving comparable to theories of land bridges from
sixty years ago.
Magnetic field,
mantle convection and tectonics
by Staff Writers
Munich, Germany (SPX) Aug 02, 2012
It is known that the
Earth's magnetic field is produced by convection currents of an
electrically conducting iron-nickel alloying the liquid core, about
3,000 kilometers below the earth's surface. The geomagnetic field is
highly variable, there are changes in Earth's magnetic field on a
multitude of spatial and temporal scales.
On
a time scale of tens to hundreds of millions of years, the
geomagnetic field may be influenced by currents in the mantle. The
frequent polarity reversals of Earth's magneticfield can
also be connected with processes in the mantle.
These are the research
results presented by a group of geoscientists in the new advance
edition of "Nature Geoscience" on Sunday, July 29th. The
results show how the rapid processes in the outer core, which flows
at rates of up to about one millimeter per second, are coupled with
the processes in the mantle, which occur more in the velocity range
of centimeters per year.
The international
group of scientists led by A. Biggin of the University of Liverpool
included members of the GFZ German Research Centre for Geosciences,
the IPGP Paris, the universities of Oslo and Utrecht, and other
partners.
It
is known that the Earth's magnetic field is produced by convection
currents of an electrically conducting iron-nickel alloy in the
liquid core, about 3,000 kilometers below the earth's surface.
The geomagnetic field is highly variable, there are changes in
Earth's magnetic field on a multitude of spatial and temporal
scales.[i really do not think
that this is known. What it is is a somewhat convincing explanation
not subject to experimental confirmation. Calling it a liquid core
does not make it so - arclein]
Above the liquid outer
core is the mantle, the rock in which behaves plastically deformable
due to the intense heat and high pressure. At the boundary between
Earth's core and mantle at 2900 km depth there is an intense heat
exchange, which is on the one hand directed from the Earth's core
into the mantle.
On the other hand,
processes within Earth's mantle in turn also affect the heat flow.
The interesting question is how the much slower flow in the solid
mantle influences the heat flow and its spatial distribution at the
core-mantle boundary, and how this will affect the Earth's magnetic
field which is produced due to the much faster currents in the
Earth's core.
Key variable heat
transfer
"The key variable is the heat flow. A cooler mantle accelerates the flow of heat from the hot core of the Earth, and in this way alters the also heat-driven convection in the Earth's core", said Bernhard Steinberger of the GFZ German Research Centre for Geosciences.
"Ocean floor
sinking into the mantle due to tectonic processes can lead to cooling
in the mantle. They cause at these sites an increased heat flow into
the cooler parts, namely until they have been heated to the ambient
temperature." That might take several hundred million years,
however.
Conversely, the hot
core of the Earth leads to the ascent of heated rocks in form of
large bubbles, so-called mantle plumes that separate from the
core-mantle boundary and make their way up to the surface of the
earth. This is how Hawaii came into existence. This increases the
local heat flux out of the earth's core and in turn modifies the
generator of the geomagnetic field.
Reversals of the
magnetic field
In the Earth's history, polarity reversals of the geomagnetic field are nothing extraordinary. The most recent took place only 780 000 years ago, geologically speaking a very short period of time.
The research team was
able to determine that in the period of 200 to 80 million years
before present, reversals initially happened more often, namely up to
ten times in hundred million years. "Surprisingly, these
reversals stopped about 120 million years ago and were absent for
nearly 40 million years," explains GFZ scientist Sachs.
Scientists presume
that the reason for this is a concurrent reorientation of the
whole mantle and crust with a shift in the geographic and magnetic
poles of about 30 degrees.
Known
as "true polar wander", this process is caused by a change
in density distribution in the mantle. If it increases the heat flux
in equatorial regions, it would presumably lead to more
frequent field reversals, if it decreases it, the field reversal
might not occur.
No comments:
Post a Comment