On 5/30/14, 2:41 AM, Dr. David Kirkby wrote:
On 28 May 2014 14:06, "Tom Holmes" <thol...@woh.rr.com> wrote:
Which begs the question: just where the heck, exactly, is the center of
the
Earth given that it is in the 'middle' of a molten and dynamic core.
I always thought that the centre was molten. There was something on the TV
in the UK a couple of weeks ago which seemed to indicate that the centre is
actually solid, although around that it is molten.
Molten, but it's a composite material under a lot of pressure, so the
transition between "liquid" and "solid" isn't like between ice and
water. Think cold peanut butter.
I did not see it all and was only watching bits of it, but it would appear
some female researcher had proven this. The proof appeared to be based on
the time of travel of shock wases from earthquakes and the different speed
they travel through solid and liquid.
Seismic evidence is how they knew it was liquid in the first place. As
you get better at doing the models, and getting better time measurements
of the seismic propagation with higher performance seismometers, you can
get a better model.
Combine that with precise orbit determination (using accurate
measurements of time and frequency from orbits) which allows accurate
gravity models (e.g. GRACE and GRACE-Follow-On)
Dave.
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