From Newsgroup: alt.fan.heinlein

A big whack that made the moon may have also created continents that move

June 19, 2024 at 11:31 am
A rendering of Earth’s collision with a Mars-size planetary object called Theia 4.44 billion years ago. Computer simulations suggest that a collision with another planetary object early in EarthrCOs history may
have provided the heat to set off plate tectonics. (Hern|in Ca|#ellas via
The New York Times)

A rendering of EarthrCOs collision with a Mars-size planetary object
called Theia 4.44 billion years ago. Computer simulations suggest that a collision with another... (Hern|in Ca|#ellas via The New York Times)More
By Lucas Joel
The New York Times
Some 4.5 billion years ago, many scientists say, Earth had a meetup with Theia, another planetary object the size of Mars. When the two worlds
collided in a big whack, the thinking goes, debris shot into space, got
locked into the orbit of the young, damaged Earth and led to the
formation of our moon.

But the collision with Theia may have done more than that, according to
a study published last month in the journal Geophysical Research
Letters. The impact may have given rise to something else: plate
tectonics, the engine that drives the motion of EarthrCOs giant
continental and oceanic plates and causes earthquakes, volcanic
eruptions and the eventual remaking of our planetrCOs surface about every
200 million years.

Earth scientists have long studied and debated the origin of plate
tectonics, and other theories have been offered. Qian Yuan, a
postdoctoral researcher at the California Institute of Technology and an author of the new paper, and his colleagues make the case for the Theia collision as the source of plate tectonics. They reason from computer simulations that the event produced the heat needed in EarthrCOs early
days to get the process going.

Tectonics starts with superheated plumes of magma from close to EarthrCOs
core rising and sitting beneath the planetrCOs plates. The plumes can
weaken the crust, and lava can erupt and push aside overriding plates.

Driven by the erupting lava, plates scrape past and collide with each
other, and they can also dive beneath other plates and into the planetrCOs interior in a process called subduction.

In earlier research, Yuan described continent-size rCLblobsrCY floating some 2,000 miles beneath EarthrCOs surface near the core. He and his team think those blobs are remnants of Theia that, delivered violently, created the
heat needed to form the first tectonics-driving plumes. The giant blobs
are believed to be connected to magma plumes, which means the blobs
could be fueling plate tectonics.

rCLSimulations show the catastrophic, moon-forming giant impact ignited
the engine that drives plate tectonics,rCY Yuan said.

Another clue is in Western Australia. There, in a place called the Jack
Hills, rocks contain crystals that formed about 4.4 billion years ago rCo
not long, geologically speaking, after Theia struck Earth.

Those crystals in Australia, called zircons, form only where there is
plate subduction, and subduction can happen only on a planet with active
plate tectonics.

Once Yuan learned that the zircons formed relatively soon after the
Theia impact, he became convinced the collision had something to do with
the start of plate tectonics.

Bradford Foley, a geophysicist at Pennsylvania State University, thinks
that the idea of plate tectonics starting from a planetary collision has merit. But it is not the only way tectonics can start, he says.

rCLThe giant impact is one possible way to make EarthrCOs core initially
very hot,rCY he said. rCLItrCOs an interesting idea that IrCOm glad to see published for the scientific community to debate, but can easily be
oversold and over-dramatized to the general public.rCY

An alternative explanation that the study does not refute, he says, is
that the planetary corerCOs initial formation may have made it hot enough
for tectonic activity to begin.

The challenge, Yuan explained, is in accurately representing the
physical states of our planet from more than 4 billion years ago.

rCLWe have confidence in our model, but does it really represent the whole true Earth?rCY Yuan said. rCLThatrCOs a question to be explored by future tests.rCY

This story was originally published at nytimes.com. Read it here.
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From Newsgroup: alt.fan.heinlein

"a425couple" wrote in message news:wCjdO.104756$iz_6.82118@fx14.iad...

A big whack that made the moon may have also created continents that move

------------------------------
https://en.wikipedia.org/wiki/Alfred_Wegener

In 1912 he presented his theory that continents drift around and were once assembled. After his death the Nazis picked up on and promoted it, which tainted the concept so much that it was buried, and only resurrected when a grad student independently noticed and popularized the proposal and thus
freed it from its political stigma.

When I studied Earth Science in the 1950's the standard explanation of mountains made no sense. There was a lot of material on Louis Agassiz but no mention of Wegener.

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From Newsgroup: alt.fan.heinlein

In alt.astronomy a425couple <a425couple@hotmail.com> wrote:

A big whack that made the moon may have also created continents that move

June 19, 2024 at 11:31 am
A rendering of Earth&#8217;s collision with a Mars-size planetary object called Theia 4.44 billion years ago. Computer simulations suggest that a collision with another planetary object early in Earth???s history may
have provided the heat to set off plate tectonics. (Hern??n Ca??ellas via The New York Times)

...

An interesting idea.

The numbers in this area are pretty big.

Planetary tidal heating (the monn and Jupiter are about 1/2 ea)
totals 60 TJ.

All the mag5+ quakes in a year totals around 600 TJ.

Tectonic activity -- all the heat coming out of the planet
from radioctive decay mostly -- amounts to around 1 billion TJ/yr.

That sounds like a big number until you think of how much sun
hits the earth in a year. About 8e12 TJ.
(Just the pissweak part of that contributed by burning fossible
fuels is only 1e10 TJ/yr).

But this all PALES in comparison with how much energy is available
for one orbiting body to slaughter another.

It's kinda a theorem of orbital disaster mechanics that the average
approach speed of 2 objects in approx the same orbit is the
average orbital speed. In the case of the earth and a similar-sized
planet orbiting the sun in similar orbits that is around 1e19 TJ.
I.e. the equivalent of around 1e10 years of tectonic activity.

Yea. That would heat things up real good. ;)
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From Newsgroup: alt.fan.heinlein

On 6/21/24 13:47, Jim Wilkins wrote:

"a425couple"-a wrote in message news:wCjdO.104756$iz_6.82118@fx14.iad...

A big whack that made the moon may have also created continents that move

------------------------------
https://en.wikipedia.org/wiki/Alfred_Wegener

In 1912 he presented his theory that continents drift around and were
once assembled. After his death the Nazis picked up on and promoted it, which tainted the concept so much that it was buried, and only
resurrected when a grad student independently noticed and popularized
the proposal and thus freed it from its political stigma.

When I studied Earth Science in the 1950's the standard explanation of mountains made no sense. There was a lot of material on Louis Agassiz
but no mention of Wegener.

OK.
Frustrating, that the name connected to a theory has so much weight
on the consideration given to that theory.

The current talk, that because it is so much smaller, Mars interior
cooled so many Billions of years before ours (and thus lost
tectonic movement and magnetism, and thus water,,,) seems
kind of lacking to me.

I read:

AI Overview
Learn more
rCa
The Earth's core has remained hot for billions of years due to a
combination of factors, including:

Radioactive decay
Isotopes like potassium-40, uranium-235, uranium-238, and thorium-232
are unstable and release energy that converts to heat, contributing up
to 90% of the Earth's internal heat.

Heat from formation
When the Earth formed around 4.5 billion years ago, it accreted from a
disk of hot, spinning material, generating a lot of heat through
collisions. This heat accounts for 5rCo10% of the Earth's core heat.

Frictional heating
Denser core material sinking to the center of the planet creates
friction, which also generates heat.

Solidifying outer core
As the liquid outer core solidifies near its boundary with the inner
core, it releases heat.

Latent heat
As the Earth cools, the core expands and releases heat into the mantle.

National Geographic Education
Core - National Geographic Education
The primary contributors to heat in the core are the decay of
radioactive elements, leftov...

Space.com
How has Earth's core stayed as hot as the sun's surface for billions of
years?
Jan 24, 2023 rCo Radioactive isotopes are not stable. They release a
steady stream of energy th...

Scientific American
Why is the earth's core so hot? And how do scientists measure ...
Oct 6, 1997 rCo Getty Images. EARTH. There are three main sources of heat
in the deep earth: (1...

Earth Observatory of Singapore
Why is the interior of the Earth hot
Earth Science FAQs - Geology and Tectonics. Why is the interior of the
Earth hot? The inte...

Phys.org
Probing Question: What heats the earth's core?
Mar 30, 2006 rCo ...

Mashable
Earth's core is wilder than you can imagine | Mashable
Jul 8, 2023 rCo A primary reason the core is profoundly hot is because
remnant heat from Earth'...
Heat moves out of the Earth slowly through convection and conduction. Convection is the transport of heat within the liquid outer core and
solid mantle, while conduction is the transport of heat through
nonconvecting boundary layers, like the Earth's plates at the surface.
Without the Earth's internal heat, the tectonic plates would stop
moving, and the Earth would likely cool down and become uninhabitable.
The Earth's core can reach temperatures of over 5,000-#C, and the inner
core is estimated to be around 9,800-#C. However, the extreme pressure
the iron in the core is exposed to, as well as other elements, may lower
the temperature by around 400-#C.

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From Newsgroup: alt.fan.heinlein

On Fri, 21 Jun 2024 16:47:23 -0400, "Jim Wilkins"
<muratlanne@gmail.com> wrote:

"a425couple" wrote in message news:wCjdO.104756$iz_6.82118@fx14.iad...

A big whack that made the moon may have also created continents that move

------------------------------
https://en.wikipedia.org/wiki/Alfred_Wegener

In 1912 he presented his theory that continents drift around and were once >assembled. After his death the Nazis picked up on and promoted it, which >tainted the concept so much that it was buried, and only resurrected when a >grad student independently noticed and popularized the proposal and thus >freed it from its political stigma.

A big issue was also that he had absolutely no mechanism for how they
could have moved

Then somebody showed that crystals showed changing magnetic fields
that would happen if the continents had moved as well as sea floor
observations backing it up
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From Newsgroup: alt.fan.heinlein

"Mad Hamish" wrote in message news:1abo7jt6qant5cvlr2jc62svdn2vpgj9iv@4ax.com...

On Fri, 21 Jun 2024 16:47:23 -0400, "Jim Wilkins"
<muratlanne@gmail.com> wrote:

"a425couple" wrote in message news:wCjdO.104756$iz_6.82118@fx14.iad...

A big whack that made the moon may have also created continents that move

------------------------------
https://en.wikipedia.org/wiki/Alfred_Wegener

In 1912 he presented his theory that continents drift around and were once >assembled. After his death the Nazis picked up on and promoted it, which >tainted the concept so much that it was buried, and only resurrected when a >grad student independently noticed and popularized the proposal and thus >freed it from its political stigma.

A big issue was also that he had absolutely no mechanism for how they
could have moved

Then somebody showed that crystals showed changing magnetic fields
that would happen if the continents had moved as well as sea floor
observations backing it up
-----------------------------------
A mechanism is easy. It had long been known that temperature increases with the depth in a mine.
From 1869: https://www.scientificamerican.com/article/on-the-temperature-of-coal-mines/

If that was all people knew, linearly projecting an observed 1F rise every
~60 feet would give the temperature of molten iron below 30 miles.
Presumably convection cells would moderate the rate of rise below that, and also create horizontal drag against the solid surface. Volcanos prove that
at least some of the rock down there is molten.

A college physics problem had us integrating the net force of gravity with depth, to determine the return time of a weight dropped into a vacuum well through Earth (of uniform density). An unexpected result of the calculus was that gravitational attraction is zero anywhere within a hollow shell (Dyson sphere), only the ball below you attracts.

https://www.reddit.com/r/askscience/comments/644elp/how_does_gravity_work_in_a_dyson_sphere/

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From Newsgroup: alt.fan.heinlein

In alt.astronomy Jim Wilkins <muratlanne@gmail.com> wrote:

"Mad Hamish" wrote in message news:1abo7jt6qant5cvlr2jc62svdn2vpgj9iv@4ax.com...

On Fri, 21 Jun 2024 16:47:23 -0400, "Jim Wilkins"
<muratlanne@gmail.com> wrote:

"a425couple" wrote in message news:wCjdO.104756$iz_6.82118@fx14.iad...

A big whack that made the moon may have also created continents that move

------------------------------
https://en.wikipedia.org/wiki/Alfred_Wegener

In 1912 he presented his theory that continents drift around and were once >>assembled. After his death the Nazis picked up on and promoted it, which >>tainted the concept so much that it was buried, and only resurrected when a >>grad student independently noticed and popularized the proposal and thus >>freed it from its political stigma.

A big issue was also that he had absolutely no mechanism for how they
could have moved

Then somebody showed that crystals showed changing magnetic fields
that would happen if the continents had moved as well as sea floor observations backing it up
-----------------------------------
A mechanism is easy. It had long been known that temperature increases with the depth in a mine.
From 1869: https://www.scientificamerican.com/article/on-the-temperature-of-coal-mines/

If that was all people knew, linearly projecting an observed 1F rise every ~60 feet would give the temperature of molten iron below 30 miles. Presumably convection cells would moderate the rate of rise below that, and also create horizontal drag against the solid surface. Volcanos prove that at least some of the rock down there is molten.

A college physics problem had us integrating the net force of gravity with depth, to determine the return time of a weight dropped into a vacuum well through Earth (of uniform density). An unexpected result of the calculus was that gravitational attraction is zero anywhere within a hollow shell (Dyson sphere), only the ball below you attracts.

...

Gauses Theorem (1777-1855). Applies to spherically symmetric masses.
May not apply to holes rilled through the earth. :)

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From Newsgroup: alt.fan.heinlein

"R Kym Horsell" wrote in message news:v5hjdf$1k4r$1@nnrp.usenet.blueworldhosting.com...

In alt.astronomy Jim Wilkins <muratlanne@gmail.com> wrote:

...
A college physics problem had us integrating the net force of gravity with depth, to determine the return time of a weight dropped into a vacuum well through Earth (of uniform density). An unexpected result of the calculus
was
that gravitational attraction is zero anywhere within a hollow shell
(Dyson
sphere), only the ball below you attracts.

...

Gauses Theorem (1777-1855). Applies to spherically symmetric masses.
May not apply to holes rilled through the earth. :)
----------------------

Would the gravity leak out the hole?

The problem set taught us how to devise formulas that describe changing conditions, that we could then integrate to determine the value at some
limit. We weren't expected to accurately model the Earth.

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