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Sat 17 Nov, 2018 11:52 pm
If we say there is an average global subsidence rate of ground (besides the uplift) of about 1 millimeters every 25 years then all ground (rock) now on surface would have sunk down to those 200 kilometers where all rock melts, recrystallizes within 4,5 billion years.
I haven´t found the exact average subsidence rate, but in principle it doesn´t matter (and 1 millimeter every 25 years sounds like a fairly modest assumption) - it doesn´t matter in the sense that if nothing else played a role here, then sooner or later all rock would get a finite age (become recrystallized).
So, the question is: wouldn´t all rock on melt sooner or later anyway?
And then some notes: Do not read this as "Aha, the Sun and Earth wasn´t created 4,5 billion years ago". I am asking a simple question that should carry its own weight. The rate of subsidence (whatever the rate may be) does give a finite age to rock when there is such and such depth where all rock melts, after so and so many years, the way I understand it.
And I do know that rock samples from the Moon, and from elsewhere in the solar system, show similar ages to those found on Earth and their age wouldn´t have anything to do with the subsidence of the ground here on Earth.
So, again, I hope you can read the question as such (the question in the title), not answering to what I have not asked.
@Marblerevealer,
You can’t average the substance rate equally over the whole planet. Some rock never goes down, at least not yet.
@Marblerevealer,
you realize that the motion of the rocks and layers of rocks, (Called tectonics) are subject to many many forces than just subsidence. eve got clar crustal wvidenc of sedimentary rocks that are over 3 billion years old and older. Weve got fossil evidence from about 3.2 to 2.8 Billion years in isolated deposits of ancient water bodies and dust bowls and ash beds.
Subsidence itself can occur in unrelated fashions, so lets think more of our planetary crust and mantles are "recycled" by yet another series of forces.
@Marblerevealer,
and the thermal gradients you are referring to will only reach a eutectic point when the rock melts reach their curie temps. thats why most all metamorphic and plutonic minerals within their rock bodies all have different curie points. A serpntinite has a much higher point than does and pegmatite, yet they are often found together in fahions that allow us to recreate their formations and dates of formations.
Give it about one and a half billion years--the whole damned planet will melt then.
@Setanta,
thatll make an interesting petrologic assemblage. We will arrive back at a condition that geologists call "square one" .
@Marblerevealer,
You mean all of Earth ending as a huge, planetwide volcano? I think that already happened.
@Setanta,
Quote:Give it about one and a half billion years--the whole damned planet will melt then
I think you are rushing things.
@maxdancona,
you didnt get the memo did you. A billion to a billion and a half years an our suns gonna expand a bit so that we would want to
1. move the earth
2. Move to one of Jupiter or Saturns moons (They will wrm up to be perhaps livable)
3. OR we continue to contemplate Uranus like the Trumpies who deny physical and climate science
@farmerman,
No. The sun won't really expand for another 5 billion years.
In 1.5 billion years the sun will radiate enough to evaporate the oceans....but not nearly enough to melt rock.
@maxdancona,
wanna bet?? stuff like quartz and native metals will melt. temps are anticipated at >650 degrees C.
Put up the cash,
@farmerman,
Are we talking 2019 dollars, or year 1500002019 dollars?
(If I invest a nickle now, assuming a conservative 7% averaged over the long term....
@farmerman,
My understanding is that in 2 billion years the Earth's temperature will be about 300F. That is almost enough to bake cookies. I don't think it will melt most rocks.
@maxdancona,
problem with these "pop science " rports we all get from the Dicovery Mag or TV are all different. I heard that in 1.25 BY, earth will be as hot as Venus, (where certain metals, quartz and feldpsars WILL melt). The main thing is, no matter what the oven temp, we wont be welcomed here na more an no more weekends at the beach. We will just have water of hydration left.
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