Earth - What is the real age?

[David Levy]

The solar system is only 4.6 billion years old so there is no going back to 100 billion.

.

Are you trying to understand what is known and how, or are you trying to contest it with your own speculation?

 

I want to understand the real age of Earth. Somehow, 4.6 Billion is not enough.

[Acme]

I want to understand the real age of Earth. Somehow, 4.6 Billion is not enough.

Somehow you are not understanding how it is enough.

[swansont]

O.K.

Let's agree that the Earth had been cooled down from 6000 °C to 32 °C in 100 My. Hence, by average, the temperature had been decreased by 59.68 °C per My. As the space is still very cold, it is expected that the Earth will continue with its rapid heat lose. Therefore, after 110 M years the temperature should be around -68 °C and after 150 My -266.4 °C.

 

 

No, I just got done explaining that this a highly nonlinear process. Doing a linear extrapolation based on that is an embossed invitation to failure.

 

If we are at 300K, the radiation is 16x higher at 600K, and another 16x higher than that at 1200K. You drop from 1200K to 600K and your radiation level drops by ~95%. There's no way you can assign an average decrease to that and draw a valid extrapolation from that.

 

And, as ajb notes, there's this fireball in the sky that also heats us (as well as radioactive decay in the core) those heating sources may be negligible when compared to radiation losses at 1200K, but not at 300K.

[Ophiolite]

 

I want to understand the real age of Earth. Somehow, 4.6 Billion is not enough.

The age of the Earth has been very clearly and accurately established through radioactive dating.[1] (Contrary to the deliberately ignorant views of Young Earth Creationists, those factors that can influence the apparent age of a sample are readily accounted for.)

 

The oldest whole rocks dated on the Earth are currently thought to be part of the Isua Greenstone Belt in Greenland. These are dated at between 3.7 and 3.8 Ga. [2] However, there is active research in other Pre-Cambrian cratons and older candidates may appear. (The Accasta Gneiss, a terrane in Australia, and another Greenland greenstone belt are all possibilities. See here.)

 

The oldest minerals on the planet are zircons from the Jack Hills in Australia. Zircons are very durable and these have been eroded from an igneous rock, then incorporated in a younger sediment. [3] The oldest of these zircons has been dated at 4.4 Ga.

 

But these post-date the actual formation of the Earth through accretion from the protoplanetary disc in the young solar system. The age of the solar system is often taken to be the time at which the first solid particles formed. This is around 4.567 to 4.568 Ga. These and the later particles accreted to form the proto-planets and planets in a relatively short time - millions, of years, not many tens of millions. [4]

 

If we date the formation of the Earth to the time of the giant impact that formed the moon, that would be around 30 million years after solar system formation. This is discussed, for example, by Jacobsen. [5].

 

The Earth has a radiogenic W-isotopic composition compared to chondrites, demonstrating that it formed while 182Hf (half-life 9 Myr) was extant in Earth and decaying to 182W. This implies that Earth underwent early and rapid accretion and core formation, with most of the accumulation occurring in ∼10 Myr, and concluding approximately 30 Myr after the origin of the Solar System. The Hf-W data for lunar samples can be reconciled with a major Moon-forming impact that terminated the terrestrial accretion process ∼30 Myr after the origin of the Solar System.

 

Keep in mind that this is an active area of research and that ages will be refined, but we should not expect any significant deviations from these numbers.

 

If the Earth was wholly molten at any point it cooled rapidly and a crust formed. (We call it a crust for a very good reason.) Thereafter surface temperature was maintained within a moderate range through the combination of solar radiation and the heat retaining properties of atmospheric gases. The contribution of heat from the interior of the Earth is miniscule in comparison.

 

What part of this do you not understand or accept? The universe has no interest in your personal incredulity.

 

References:

 

1. http://www.geo.cornell.edu/geology/clas ... ture04.pdf

2. Rollinson, H. The metamorphic history of the Isua Greenstone Belt, West Greenland Geological Society, London, Special Publications 2002 v. 199, p. 329-350

3. http://www.geology.wisc.edu/~valley/zir ... Nature.pdf

4. Krot, A.N. et al Origin and chronology of chondritic components: A review Geochimica et Cosmochimica Acta 73 (2009) 4963–4997

5. Jacobsen, S.B. THE Hf-W ISOTOPIC SYSTEM AND THE ORIGIN OF THE EARTH AND MOON

Annual Review of Earth and Planetary Sciences Vol. 33: 531-570 May 2005

[studiot]

Well I'm glad Ophiolite has chosen to return.

 

That was a professional summary of current knowledge.

 

+1

 

[David Levy]

Thanks

I'm not sure that I fully understand your following explanation

 

The Earth has a radiogenic W-isotopic composition compared to chondrites, demonstrating that it formed while 182Hf (half-life 9 Myr) was extant in Earth and decaying to 182W. This implies that Earth underwent early and rapid accretion and core formation, with most of the accumulation occurring in ∼10 Myr, and concluding approximately 30 Myr after the origin of the Solar System. The Hf-W data for lunar samples can be reconciled with a major Moon-forming impact that terminated the terrestrial accretion process ∼30 Myr after the origin of the Solar System.

 

Therefore, let's summarize the evidences:

The Earth had been formed about 4,550Myr ago.

In less than 100 My (or even 30 My?) it's temperature had been decreased dramatically from 6000 to about 32.

However, after cooling down to 32 it keeps that temperature for the coming 4,400 My.

Please also be aware that it took some time to the Earth to establish the magnetic core. Therefore, during this time it had been bombarded by significant amount of heat from the Sun. Therefore, it is expected that the temperature of Earth should actually increase in its first phase of life. However, just after setting the magnetic shield it had a real chance to decrease its temperature.

So, with all this information please answer the following:

How long it took the Earth to establish the magnetic shield? (Not just the iron core but real shield)

Without this shield, how the temperature on Earth should be affected?

After setting the shield, what is the expected heat dissipation which is requested to decrease the Earth temperature from over 6000 to 32?

How could it be that the Earth had been set the magnetic shield and cooled down dramatically in less than 100 My, while it keeps its temperature at the same level for the coming 4400 my.

Please explain and proof by evidence.

Edited March 25, 2015 by David Levy

[swansont]

The solar radiation didn't turn on all of the sudden — it would set the asymptotic value the earth's temperature would reach. Then you hit steady-state. Energy in = energy out. You can get a rough idea of this temperature by using the Stefan-Boltzmann law, though it ignores the greenhouse effect of the atmosphere.

 

Why do you think the magnetic field would affect the temperature?

[imatfaal]

David - are you actually reading the detailed and scholarly answers you are receiving or just skipping through them to your next piece of guesswork.

 

Your response to SwansonT's message regarding the rate of cooling through radiation varying with the fourth power made it quite clear that you had missed the point entirely through either lack of understanding or failure to actually read the post.

 

Do you know understand and acknowledge that your post with a linear average was complete nonsense?

 

You seem to ignore the empirical basis of Ophiolite's post and latch onto a few key words and set off on a new tangent. Basically you got a physics post from a physicist and a geology post from a geologist, seemed to ignore the real import of both of them, and ploughed on with your notions regardless.

 

If you are convinced that the earth's age is presently being wrongly estimated then we will move this thread to Speculations and you will have to abide by the rules of that forum. If you want to ask questions to fully understand how we come to our current estimates then you need to engage with the answers you receive.

[Greg H.]

Let's start with the first element:

Sun heat contribution – for the last 4.4 Billion years the sun keeps the earth at the same temperature (more or less). With this assumption, even if we go back 100 Billion year, than the temperature on Earth should be the same. However, somehow, we must increase this temperature. Therefore, let assume that the max temperature to hold life is 50 °C. That was 3.5 Billion years ago.

So, 3.5 Billion years ago, the temperature was 50 °C. If the temperature today is 30, then it had been decreased by 20 °C in 3.5 Billion years.

Now, let use the second section:

The heat loss falls off, as the temperature difference decreases- So, in 3.5 Billion, the temperature had been falls by 20 °C .

Let's use 3.5 Billion year as a constant time segment and the 20 °C as heat increase segment.

Let's assume that as we move backwards in time, for each constant time sector, the heat increase should be doubled.

Hence...

You're wrong, which is what these experts in their field have been trying to tell you. You can't just make these assumptions - there are formulas that would give you the rates of cooling - I am assuming you could use calculus to derive a graph that showed the rate of cooling over time, but it's not just as simple as assuming the temperate change doubles ever so often.

 

I addition, your notion fails to account for things that could have temporarily raised the average temperature - impacts with large objects, for example.

[Essay]

 

Let's start with the first element:

Sun heat contribution – for the last 4.4 Billion years the sun keeps the earth at the same temperature (more or less). With this assumption....

...just an fyi that I don't think anyone else mentioned, which might help with your accounting for heat.

 

...plus, you can find some extra good info at wikipedia about the "Faint Young Sun Paradox" ...iirc.

===

 

 

...magnetic field doesn't relate to this topic, right?

Thanks

I'm not sure that I fully understand your following explanation

 

Therefore, let's summarize the evidences:

The Earth had been formed about 4,550Myr ago.

In less than 100 My (or even 30 My?) it's temperature had been decreased dramatically from 6000 to about 32.

However, after cooling down to 32 it keeps that temperature for the coming 4,400 My.

Right, roughly, within 30 or 100 My, after the formation, a crust formed ...as Ophiolite mentioned above.

 

After the crust formed, there was no longer 6000 degree molten stuff in direct contact with the icy depth of space (or an atmosphere). The crust insulated the hot magma, from the "heat sink" of deep space, so the surface of the crust cooled and mostly became heated by the sun (plus some help of greenhouse effect in atmosphere).

 

Don't you think the crust formation should make a big difference, if you're talking about the surface temperature?

~

Edited March 25, 2015 by Essay

[David Levy]

Why do you think the magnetic field would affect the temperature?

 

Thanks for the question.

Let's look at the "sister planet" - Venus:

https://en.wikipedia.org/wiki/Venus#Magnetic_field_and_core

Venus is a terrestrial planet and is sometimes called Earth's "sister planet" because of their similar size, mass, proximity to the Sun and bulk composition"

It has no real magnetic shield:

"Venus's small induced magnetosphere provides negligible protection to the atmosphere against cosmic radiation."

The main reason for that is none functionality of the dynamo at Venus. However, the requirements for dynamo are as follow:

"A dynamo requires three things: a conducting liquid, rotation, and convection."

Without the dynamo, there is no magnetic shield:

"No internal geodynamo is available to drive a magnetic field. Instead, the heat energy from the core is being used to reheat the crust"

Hence, Venus is the hottest planet in the solar system:

"mean surface temperature of 735 K (462 °C; 863 °F), Venus is by far the hottest planet in the Solar System"

The dynamo is requested three elements: a conducting liquid, rotation, and convection."

Without those elements, there is no dynamo, there is no magnetic shield and there is a significant increase in the temperature.

Those three elements had not been developed properly in Venus. Hence, without those elements, it is expected that also on earth the temperature could be significantly high.

 

 

You're wrong, which is what these experts in their field have been trying to tell you. You can't just make these assumptions - there are formulas that would give you the rates of cooling - I am assuming you could use calculus to derive a graph that showed the rate of cooling over time, but it's not just as simple as assuming the temperate change doubles ever so often.

 

I addition, your notion fails to account for things that could have temporarily raised the average temperature - impacts with large objects, for example.

 

Therefore, it isn't just an issue of formulas and mathematics. It's an issue of fundamental requirements on Earth to establish the basic elements for heat dissipation and protection.

The science must proof that all the requested elements had been developed in Earth in a very short time before starting any calculation.

How could it be that in Venus (even after 4500 My) those elements had not been properly developed, while in Earth (which is nearby and has similar size) it had been developed almost instantly?

Edited March 25, 2015 by David Levy

[Acme]

... Without the dynamo, there is no magnetic shield: "No internal geodynamo is available to drive a magnetic field. Instead, the heat energy from the core is being used to reheat the crust"

First, you can do away with the distracting formatting; it only serves to make already confused writing harder to read.

 

Second, it is not the heat that directly makes a dynamo work, it's the convection in the liquid core. When Earth cools sufficiently, the geodynamo will cease to operate and our magnetic field will fail, but this is not going to make Earth heat up.

 

...

...Without those elements, there is no dynamo, there is no magnetic shield and there is a significant increase in the temperature.

Again, no. Loosing a magnetic field does not cause heating. The magnetic field fails because the core cools.

 

... Therefore, it isn't just an issue of formulas and mathematics. It's an issue of fundamental requirements on Earth to establish the basic elements for heat dissipation and protection.

The science must proof that all the requested elements had been developed in Earth in a very short time before starting any calculation.

In a word, no. Whether it's your English, or your understanding, or both, what you just wrote there is gibberish.

[Robittybob1]

First, you can do away with the distracting formatting; it only serves to make already confused writing harder to read.

 

Second, it is not the heat that directly makes a dynamo work, it's the convection in the liquid core. When Earth cools sufficiently, the geodynamo will cease to operate and our magnetic field will fail, but this is not going to make Earth heat up.

 

Again, no. Loosing a magnetic field does not cause heating. The magnetic field fails because the core cools.

 

In a word, no. Whether it's your English, or your understanding, or both, what you just wrote there is gibberish.

Could the incoming solar radiation contribute to the heating of the surface? Obviously it is a combination of the atmosphere and incident radiation.

 

"Venus's small induced magnetosphere provides negligible protection to the atmosphere against cosmic radiation."

Once the surface is kept hot, there is less potential for the underlying material to cool, so the whole planet gets hotter.

Is this a possible consequence of the small induced magnetosphere on Venus.

Michel van Biezen talks of Venus being tipped over (making it orbit in the opposite direction to most of the other planets) at an early stage, so a moon or some other massive object must have collided with Venus to cause this. The loss of a moon and its slow rotation could also be a significant factor.

1 day (passage of the Sun from horizon to horizon) on Venus is equal to 116d 18h 0m on Earth. That is a very slow rotation. (Is it the slowest of all the planets in our SS?) http://www.universetoday.com/47898/length-of-day-on-venus/ (note a full rotation = 243 days)

 

 

The length of day on Venus is 243 Earth days.

Read that again, it’s not a year, but the length of a single day. In fact, a year on Venus is only 224.7 days, so a day on Venus is longer than its year. And things get even stranger. Venus rotates backwards. All of the planets in the Solar System rotate counter-clockwise when you look at them from above. But Venus turns clockwise.

Edited March 25, 2015 by Robittybob1

[Acme]

Could the incoming solar radiation contribute to the heating of the surface? Obviously it is a combination of the atmosphere and incident radiation. ...

Yes the solar radiation heats the surface and yes the atmosphere can trap heat. But primarily Venus is as hot as it is today because of its proximity to the Sun, not because of its core temperature or lack of a magnetic field. Venus is in a surface temperature equilibrium just as are the other planets and notwithstanding variations in Sol's output. That is to say, that if the Sun's output were to increase, then the planets' surface temperatures would rise until a new equilibrium was reached and if the Sun's output decreased, then the planets' surface temperatures would decrease until reaching a new equilibrium. In any case, the cores will continue to cool until at some point the cores will reach equilibrium as well.

...Once the surface is kept hot, there is less potential for the underlying material to cool, so the whole planet gets hotter....

A hotter surface may slow heat loss from the interior, but it does not add heat to the interior.

 

Heat transfer

...Heat transfer always occurs from a region of high temperature to another region of lower temperature...

[swansont]

 

Thanks for the question.

Let's look at the "sister planet" - Venus:

https://en.wikipedia.org/wiki/Venus#Magnetic_field_and_core

Venus is a terrestrial planet and is sometimes called Earth's "sister planet" because of their similar size, mass, proximity to the Sun and bulk composition"

It has no real magnetic shield:

"Venus's small induced magnetosphere provides negligible protection to the atmosphere against cosmic radiation."

The main reason for that is none functionality of the dynamo at Venus. However, the requirements for dynamo are as follow:

"A dynamo requires three things: a conducting liquid, rotation, and convection."

Without the dynamo, there is no magnetic shield:

"No internal geodynamo is available to drive a magnetic field. Instead, the heat energy from the core is being used to reheat the crust"

Hence, Venus is the hottest planet in the solar system:

"mean surface temperature of 735 K (462 °C; 863 °F), Venus is by far the hottest planet in the Solar System"

The dynamo is requested three elements: a conducting liquid, rotation, and convection."

Without those elements, there is no dynamo, there is no magnetic shield and there is a significant increase in the temperature.

Those three elements had not been developed properly in Venus. Hence, without those elements, it is expected that also on earth the temperature could be significantly high.

 

 

 

Therefore, it isn't just an issue of formulas and mathematics. It's an issue of fundamental requirements on Earth to establish the basic elements for heat dissipation and protection.

The science must proof that all the requested elements had been developed in Earth in a very short time before starting any calculation.

How could it be that in Venus (even after 4500 My) those elements had not been properly developed, while in Earth (which is nearby and has similar size) it had been developed almost instantly?

 

You haven't established how cosmic rays affect heating the planet. Which is moot, because the "shielding" we have against them on earth is simply funneling them toward the poles; the energy is still deposited. So I ask again, how does the magnetic field allegedly affect the temperature of the planet?

 

AFAIK, one thing we don't know is if Venus had a geodynamo-generated magnetic field in the past. Only that it currently does not.

 

"similar…proximity to the Sun" is not a particularly precise assessment. The orbit is at about .72 AU, meaning Venus gets about twice the solar radiation that we do. Not something you can ignore on the topic of heating.

 

You also didn't quote the part about the runaway greenhouse effect that adds to the high temperature.

[Robittybob1]

Yes the solar radiation heats the surface and yes the atmosphere can trap heat. But primarily Venus is as hot as it is today because of its proximity to the Sun, not because of its core temperature or lack of a magnetic field. Venus is in a surface temperature equilibrium just as are the other planets and notwithstanding variations in Sol's output. That is to say, that if the Sun's output were to increase, then the planets' surface temperatures would rise until a new equilibrium was reached and if the Sun's output decreased, then the planets' surface temperatures would decrease until reaching a new equilibrium. In any case, the cores will continue to cool until at some point the cores will reach equilibrium as well.

A hotter surface may slow heat loss from the interior, but it does not add heat to the interior.

 

Heat transfer

The analogy I was thinking of is compost piles, with more insulation around them you do get a higher core temperature. So the composition of the core of the compost is not changed by the insulation but with the heat being unable to escape the core temperature will rise. The same would happen to a planet if the heat can't escape the core will be hotter, for the heat production (principally radioactivity) will be the same.

It does not add heat to the core but enables it to get hotter.

Edited March 25, 2015 by Robittybob1

[Acme]

The analogy I was thinking of is compost piles, with more insulation around them you do get a higher core temperature. So the composition of the core of the compost is not changed by the insulation but with the heat being unable to escape the core temperature will rise. The same would happen to a planet if the heat can't escape the core will be hotter, for the heat production (principally radioactivity) will be the same.

You said: "It does not add heat to the core but enables it to get hotter."

Think about that. Getting hotter means adding heat.

As long as the core is hotter than the surface, it loses heat to the surface. The insulating factor only changes the rate of that loss, it does not raise the core temperature.

[Robittybob1]

You said: "It does not add heat to the core but enables it to get hotter."

Think about that. Getting hotter means adding heat.

As long as the core is hotter than the surface, it loses heat to the surface. The insulating factor only changes the rate of that loss, it does not raise the core temperature.

No I don't think that is true, as I said I have experienced it with making compost, insulation allows the terminal temperature to be hotter. I doubt whether that is because the composition changes. Is there some other example where the same amount of heat results in a higher core temperature. Home insulation would be an example. The same heating device gets the same home hotter when the rooms are adequately insulated.

Without the change in sulation getting hotter would mean adding heat.

We disagree potentially on your last sentence.

 

 

As long as the core is hotter than the surface, it loses heat to the surface. The insulating factor only changes the rate of that loss, it does not raise the core temperature.

That would be true if all the heat was present at the beginning but more heat is being produced as time go on.

Edited March 25, 2015 by Robittybob1

[Acme]

No I don't think that is true,

That's the problem.

 

That would be true if all the heat was present at the beginning but more heat is being produced as time go on.

Once the planet has formed, there is no more fuel for the fire. Barring very large impacts of course. Presuming that Venus has decaying radioisotopes in the core, these do not make the core hotter than when the planet formed, they only keep it hot longer.

 

Edit: In you compost pile example, the bacteria which are generating the heat are reproducing, i.e. more of them come on the scene. The radioisotopes in a core are not reproducing, they are decaying.

Edited March 25, 2015 by Acme

[MigL]

To be fair to David, a rapidly collapsing magnetic field could induce some heating.

This repeated set-up and collapse of magnetic fields is how induction heating works.

 

The effect would certainly not be sufficient to explain Venus as David seems to think.

[Robittybob1]

That's the problem.

 

Once the planet has formed, there is no more fuel for the fire. Barring very large impacts of course. Presuming that Venus has decaying radioisotopes in the core, these do not make the core hotter than when the planet formed, they only keep it hot longer.

 

Edit: In you compost pile example, the bacteria which are generating the heat are reproducing, i.e. more of them come on the scene. The radioisotopes in a core are not reproducing, they are decaying.

I challenge you to find a reference that backs up your presumption:

 

Presuming that Venus has decaying radioisotopes in the core, these do not make the core hotter than when the planet formed, they only keep it hot longer.

So do you think the core temperature was the hottest immediately on forming? I'm sure you are wrong about that. But you made the statement so I challenge you to back it up.

[Acme]

I challenge you to find a reference that backs up your presumption:

So do you think the core temperature was the hottest immediately on forming? I'm sure you are wrong about that. But you made the statement so I challenge you to back it up.

I and the rest have given all the facts necessary to answer the OP. You and David Levy can choose to ignore them at your leisure.

[Robittybob1]

I challenge you to find a reference that backs up your presumption:

So do you think the core temperature was the hottest immediately on forming? I'm sure you are wrong about that. But you made the statement so I challenge you to back it up.

Wikipedia check up on Thermal gradient, reminded me that in the early Earth the amount of radioactive material was much higher, so the heat being produced early on was at a much greater rate. http://en.wikipedia.org/wiki/Geothermal_gradient

 

Geothermal gradient is the rate of increasing temperature with respect to increasing depth in the Earth's interior. Away from tectonic plate boundaries, it is about 25 °C per km of depth (1 °F per 70 feet of depth) in most of the world.[1] Strictly speaking, geo-thermal necessarily refers to the Earth but the concept may be applied to other planets. The Earth's internal heat comes from a combination of residual heat from planetary accretion, heat produced through radioactive decay, and possibly heat from other sources. The major heat-producing isotopes in the Earth are potassium-40, uranium-238, uranium-235, and thorium-232.[2] At the center of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 GPa(3.6 million atm).[3] Because much of the heat is provided by radioactive decay, scientists believe that early in Earth history, before isotopes with short half-lives had been depleted, Earth's heat production would have been much higher. Heat production was twice that of present-day at approximately 3 billion years ago,[4] resulting in larger temperature gradients within the Earth, larger rates of mantle convection and plate tectonics, allowing the production of igneous rocks such as komatiites that are not formed anymore today.[5]

So the early Earth was hotter but was it the hottest immediately on forming?

I and the rest have given all the facts necessary to answer the OP. You and David Levy can choose to ignore them at your leisure.

 

That was not sufficient to support your presumption.

 

Looking at the radiation of the Earth's surface http://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law#Temperature_of_the_Earth

But this is from our current quite cold temperatures.

I think it is important that Dave understands the ideas behind the Iron Catastrophe.

http://en.wikipedia.org/wiki/Iron_catastrophe

 

The iron catastrophe was a major event early in the history of Earth. The original accretion of the Earth's material into a spherical mass is thought to have resulted in a relatively uniform composition. While residual heat from the collision of the material that formed the Earth was significant, heating from radioactive materials in this mass gradually increased the temperature until a critical condition was reached. As material became molten enough to allow movement, the denser iron and nickel, evenly distributed throughout the mass, began to migrate to the center of the planet to form the core. The gravitational potential energy released by the sinking of the dense NiFe globules, along with any cooler denser solid material is thought to have been a runaway process, increasing the temperature of the protoplanet above the melting point of most components, resulting in the rapid formation of a molten iron core covered by a deep global silicate magma. This event, – an important process of planetary differentiation, occurred at about 500 million years into the formation of the planet.[1]

From that it is clear that the Earth built up heat over a period of some 500 million years, whether that coincides with the maximum it doesn't say. From that it appears the surface temperature never got that hot, hence the internal heat of the Earth has persisted for such a long time (4.6 by).

Edited March 26, 2015 by Robittybob1

[Essay]

....

I think it is important that Dave understands the ideas behind the Iron Catastrophe.

http://en.wikipedia.org/wiki/Iron_catastrophe

From that it is clear that the Earth built up heat over a period of some 500 million years, whether that coincides with the maximum it doesn't say. From that it appears the surface temperature never got that hot, hence the internal heat of the Earth has persisted for such a long time (4.6 by).

...very interesting information!

 

It's more of a semantic difference, but I noticed they use the term "protoplanet" [...increasing the temperature of the protoplanet above the melting point of most components...] in their description.

 

It sounds as if "the planet" can't start cooling until it is completely formed and organized enough to be defined as a planet, which occurs after some "heat building" phase that occurs while the definition of protoplanet still applies, or when the definition of "the formation of the planet" is still applied.

 

Once the planet is formed and well-defined, with a crust, then these other points above should make more sense as explanations, istm.

 

~

[Robittybob1]

...very interesting information!

 

It's more of a semantic difference, but I noticed they use the term "protoplanet" [...increasing the temperature of the protoplanet above the melting point of most components...] in their description.

 

It sounds as if "the planet" can't start cooling until it is completely formed and organized enough to be defined as a planet, which occurs after some "heat building" phase that occurs while the definition of protoplanet still applies, or when the definition of "the formation of the planet" is still applied.

 

Once the planet is formed and well-defined, with a crust, then these other points above should make more sense as explanations, istm.

 

~

I am not a geologists and I'd like Ophilite to comment, for I keep seeing geological formations that make me think the surface of the planet was never really totally molten, but that is too much from a layman's point of view and not an expert.