Re: Plate techtonics and asteroid hits

in article timberwoof.spam-C2CCF2.12114623062007@xxxxxxxxxxxxxxxxxxxxxxxx,
Timberwoof at timberwoof.spam@xxxxxxxxxxxxxxxxxxxxx wrote on 6/23/07 12:11
PM:

In article <C2A2914C.1EA9%georgee3@xxxxxxxxxxxxx>,
George Evans <georgee3@xxxxxxxxxxxxx> wrote:

in article l3Uei.17496$y_7.12928@xxxxxxxxxxxxxxxxxxxxxxxxxx, John Harshman at
jharshman.diespamdie@xxxxxxxxxxx wrote on 6/22/07 10:56 AM:

UC wrote:

We have learned about the plates upon which the continents ride. Is there
any evidence or even speculation that these fractures in the Earth's
surface were not part of the original equipment of the planet Earth?

Yes. There is evidence that plates and plate tectonics (note spelling) as we
know them were not features of the earliest earth. Too hot a planet doesn't
allow for the relative stability we see in that past 3+ billion years.

Is there any suggestion that they are residual damage from asteroid
impacts?

None whatsoever.

Shame on you, John. Why do you answer such an open ended question so
dogmatically? Plate tectonics itself is somewhat speculative now, since the
only part of the mantle that is in convective motion is the upper 400 miles.

Now I recall reading about someone's deep seismic survey of a section of the
Earth off the west coast of the Americas, that found a blob of material
descending deep into the mantle.

I know there are subduction zones where the subducted plate is plunging down
deeper than 400 miles. What is missing is any regular signs of convective
upwellings, as far as I remember.

The great convective cells that the theory hypothesized weren't found. And
with hundreds of asteroid craters found so far, still visible is the crust,
it is a reasonable speculation that recent impacts have caused the outer
section of mantle to heat up and set PT in motion.

You could do the thermal calculations. There are data on the size
distributions of asteroids and stuff, as well as their typical orbital speeds.
Factor in some number of impacts and the heat generated should be a
straightforward calculation.

Indeed, the Earth must have grown very hot as it accreted matter while
forming. And the Iron Catastrophe was a serious bit of convective action.
Since the Earth was much hotter back then, and cooling on the outside, it
seems to me that mantle convection would have started then.

It seemed reasonable to me, too. But I don't think the data is supportive of
"deep" cell convection.

George Evans

.

Relevant Pages

  • Re: Plate techtonics and asteroid hits
    ... There is evidence that plates and plate tectonics (note ... spelling) as we know them were not features of the earliest earth. ... material descending deep into the mantle. ... it is a reasonable speculation that recent ...
    (talk.origins)
  • Re: heat corpuscles in the mantle
    ... >> Subcrustal Ice Earth Model ... >> Ganymede's crust probably consists of a thick layer of water ice. ... >> hypothetical processes of subduction and convection. ... >> The convection hypothesis comes under critical scrutiny in: Is mantle ...
    (sci.geo.geology)
  • Re: Plate techtonics and asteroid hits
    ... Is there any evidence or even speculation that these fractures in ... Too hot a planet doesn't allow for the relative stability we see in ... mantle to heat up and set PT in motion. ... formation to heat up the planet and start convection. ...
    (talk.origins)
  • Re: heat corpuscles in the mantle
    ... >>> Subcrustal Ice Earth Model ... >>> Ganymede's crust probably consists of a thick layer of water ice. ... >>> hypothetical processes of subduction and convection. ... >>> mantle convection, and develops some helpful Retic's Rules. ...
    (sci.geo.geology)
  • Re: Tectonic plates and seams
    ... attempt to discuss your stationary Earth notion of convection ... Thermally driven convection cells in other words,which leaves you ... If you are hung up on the rotational dynamics of a flexible/molten ...
    (sci.geo.geology)
Loading