Criticism wanted: geologically old terrestrial world

[rthorvald]

I am picking up my solar system again after the detour with Gallia, and need some input on this planet: i am trying to make a very old terrestrial world. How real does this look/feel? Could it be more pronounced? I?d be grateful for any feedback.



PS to mr. Edwards: as you can see, i have been stealing some of your clouds again. Please tell me if you are getting fed up with this behaviour...

-rthorvald

[selden]

It's hard to criticize without knowing what evolutionary model you're basing your design on and what features you're trying to include.

You do seem to be showing a land-to-water surface ratio that's somewhat larger than the Earth's, so that does seem consistant with an older Earth-like planet.

My superficial knowledge of current plate techtonic theories says that in later cycles (of plates separating and then merging again), the land to water surface ratio increases. (Which suggests to me that if the volume of water doesn't change much, then the average ocean depths must be greater: the altitudes of the continental shelves must be higher.) In any given cycle, there are bound to be times when there are lots of high mountains (as leading plate edges collide or rub against one another) and others when older mountains have been worn down. There also will be times when the individual plates are separated and when they've merged into a single super-continent.

I seem to recall that the Earth's plates tend to form a new super-continent every 250MYears or so. (Hmm -- that's about the same as the sun's orbital period around the galactic center, but I don't see how they could be related.)

One of the problems with cloud designs is that they're affected by the underlying topology, so clouds lifted straight off the Earth won't be the best match for a planet with a super-continent.

I'd guess that the weather patterns also would tend to make flat, central areas drier (as with Africa and Australia). while elevated central regions or mountainous regions would tend to encourage precipitation (as with Eurasia).

[rthorvald]

It's hard to criticize without knowing what evolutionary model you're basing your design on and what features you're trying to include.

I want it to be eroded, worn down. So i made very smooth coastlines, and sampled most of the interiors from Africa. Exept for a small, but conspicious mountain range on the southeastern coast, that i put in for contrast (so that everything else looks really old), mostly dull, smooth features everywhere. One of the things i am concerned about though, is the green areas: i am not sure how much vegetation should be visible - how fertile would a really old Earth be?

One of the problems with cloud designs is that they're affected by the underlying topology, so clouds lifted straight off the Earth won't be the best match for a planet with a super-continent.

The weather pattern is what i am most interested in: i guessed that it would be less chaotic than on a younger world. So the cloudmap is sampled from the lighter areas of one of Edwards maps, but with more opaque white. Maybe it should be the other way around; more transparent - if the planet loses atmosphere with time? (Is that generally true?)

All in all, i guess everything should look a bit dull, but how to have it look dull in an interesting way... Most important is, does the map look real?

-rthorvald

[selden]

It's hard to criticize without knowing what evolutionary model you're basing your design on and what features you're trying to include.

I want it to be eroded, worn down. So i made very smooth coastlines, and sampled most of the interiors from Africa. Exept for a small, but conspicious mountain range on the southeastern coast, that i put in for contrast (so that everything else looks really old),

Those mountains would imply that the super-continent is just starting to pull apart again (mountains wrinkle up on leading edges of plates), so you might want to have a bay cutting into the eastern or southern coast, or both, where that plate is starting to pull away. If tectonics stopped just after the last super-continent formed, then mountains would tend to be toward the interior: along the colliding edges of the plates.

mostly dull, smooth features everywhere. One of the things i am concerned about though, is the green areas: i am not sure how much vegetation should be visible - how fertile would a really old Earth be?

I'd expect something like a gigantic Australia. The central regions of the continent are going to be dry.

One of the problems with cloud designs is that they're affected by the underlying topology, so clouds lifted straight off the Earth won't be the best match for a planet with a super-continent.

The weather pattern is what i am most interested in: i guessed that it would be less chaotic than on a younger world. So the cloudmap is sampled from the lighter areas of one of Edwards maps, but with more opaque white. Maybe it should be the other way around; more transparent - if the planet loses atmosphere with time? (Is that generally true?)

Your planet seems to have plenty of water, so I'd expect plenty of clouds, too, at least over the ocean, mountain and coastal regions.

(This paragraph is just vague ramblings.) How the atmosphere evolves has to depend on the chemical reactions that have been going on. A lot of gasses are provided by volcanoes and then get modified by organic and inorganic processes. Look at Venus: it's hotter than the Earth (more chemical activity), doesn't seem to have much volcanic activity now, but certainly hasn't lost much of its atmosphere!

All in all, i guess everything should look a bit dull, but how to have it look dull in an interesting way... Most important is, does the map look real?

Well, maybe

There's plenty of water, so I'd expect to see more green areas (and clouds over land) near those coasts where the prevailing blow inland than where it blows away from the land. In other words, more greenery on northwestern coasts (in the northern hemisphere) and on southeastern (in the southern) than on the southwestern or northeastern.

Bear in mind that I'm no climatologist, so these guesses could be way off!

[Dollan]

If it is an older planet that is also being effected by an aging sun, then likely there will be almost total cloud cover as the oceans begin to evaporate, however slowly at first. As the amount of water in the atmosphere grows, the pressure and greenhouse effect will grow, until a threshold is reached and the remaining water evaporates, leaving behind a very Venusian-like planet.

However, if it is just the planet that is very old, and the sun is a low mass star and still well within its main sequence life span, then perhaps the geological cycle is slowing as the planetary core slowly looses energy and cools. A good example of what such a world might be like can be found at http://www.eponaproject.com/

Of course, you could assume that the internal fires of a planet will *not* cool, in which case you could have a planet that is 5+ billion years old, but which really does not show any difference from what it was when it was less than 4 billion.

An interesting note: the interior of this supercontinent would indeed be very dry, possibly close to uninhabitable by Human standards, such as a mega-Sahara, or a mega-Kalahari, as is generally agreed to have been the case with the interior of Pangaia. However, there is some thought now that mega-monsoons ravaged the interior on a yearly basis. Here are some brief links that I have on hand:

http://www.gsajournals.org/gsaonline/?r ... -7613(2002)030%3C1127:SILPAC%3E2.0.CO%3B2

http://www.bbc.co.uk/science/horizon/20 ... tery.shtml

http://www.scotese.com/ejurclim.htm

So, in that case, you could conceivably show a cloud map with really massive cloud cover over the interior, depending on the time of year.

Hope this helps.

And by the way, I do love the map!

...John...

[rthorvald]

However, if it is just the planet that is very old, and the sun is a low mass star and still well within its main sequence life span, then perhaps the geological cycle is slowing as the planetary core slowly looses energy and cools

The star is HIP 98959, which is a G2 V. I got the planet off Stargen, it is slightly smaller than the Earth and a bit closer to the star.

Thank you for your comments, and you too, Selden; this is exactly the info and thoughts i need to get a good result.

The reason i want such detail is, i want the Solarsys to have visible history. I think it will feel more like an actual place if there?s some depht to it, not just a bunch of planets.

-rthorvald

[eburacum45]

One thing to bear in mind about water loss; perhaps 20% of the Earth's ocean water might be lost to subduction in the next billion years; so the continental shelf areas might well be more exposed in an older world.

The most important effect on the Earth is likely to be the gradual warming of the sun; so this planet, if is was once Earth-like, will likely to be getting hotter and more inhospitable.

By coincidence, I am working on a moist greenhouse world (Oshiq) at the moment; a lot of the lowlands are replaced by salt flats and gypsum pans...

but I think your image is much better than any I can conjure up...

[maxim]

A geologically old planet would probably not look like you would expect it:

1. The erosion process is much slower than the process of mountain folding caused by continental drifting. We can differentiate three main periods of rock folding in earth history, and the results of all three are still visible. So it is to expect that - as long as the plate movement doesn't stop - the number and size of hilly or mountaineous areas will increase with time, not decrease.

2. I'm not sure that - as selden says - the land/water ratio will increase. Instead I would expect the continental crust/ocean crust ratio to increase. The material differentiation processes along the subduction zones will cause light materials to ascend, becoming new parts of continents, whereas the heavy materials will subside back into the mantle zone, forming new ocean crust in later times. In the very, very long range this might cause the ocean crust to become more and more heavy and so the ocean floor might become deeper in relation to the continents. But I believe it's more likely that the differentiated heavy material will sink deeper into the earth mantle and be replaced by lighter undifferentiated material in the upper mantle layer. The overall result would be bigger continents - but as the overall amount of water wouldn't change I would expect larger swallow sea areas instead of a larger visible land mass.

3. The plate movement won't stop as long as the core won't cool down considerably, and as long as there is water available. Some say plate movement may even increase in the future - don't know if this is true. Plate movement as we know it is supposed to have started 800 million years ago - there are actual researches, based on the chemical structures of micro diamonds that predict that it might have started 2 billion years ago.

4. The soil coverage of the earth is going to increase constantly. You might bear in mind that there was no such coverage (or any plants) 600 million years ago - before live starts to conquer land at all. So one might expect a more closer vegetation coverage in the future - as long as the conditions allow for live.


All in all I can't see any future planetary conditions that could be described by words like 'worn down' as long as geological processes remain dynamic, which they will for a very long time.

maxim

[Ynjevi]

I seem to recall that the Earth's plates tend to form a new super-continent every 250MYears or so. (Hmm -- that's about the same as the sun's orbital period around the galactic center, but I don't see how they could be related.)

Actually Pangaea formed about 300 million years ago, and the next supercontinent will appear in about 250 million years, so the cycle may be around half a billion years or more. Previous supercontintent, Rodinia existed 1,000-700 million years ago or so.

---

As Dollan already wrote, very old terrestial world would most likely be like Venus. As its parent star ages, its luminosity increases and the planet starts to be hotter and hotter, until the oceans evaporate. Released water vapor will act as powerful green house gas resulting in huge temperature rise. After that, tectonic processes cease to operate because there is no longer water to keep ocean floor lithe. No longer there would be any subtle way to release heat, so the whole crust probably melt catastrophically.

Before that, I cannot see that the planet is much different than the Earth today. Likely there wouldn't be ice age periods anymore, so it wouldn't have any ice caps.

There's plenty of water, so I'd expect to see more green areas (and clouds over land) near those coasts where the prevailing blow inland than where it blows away from the land. In other words, more greenery on northwestern coasts (in the northern hemisphere) and on southeastern (in the southern) than on the southwestern or northeastern.

Good to bear in mind when you design new planets. Ocean currents and vegetation zones are way too often just forgotten.

2. I'm not sure that - as selden says - the land/water ratio will increase. Instead I would expect the continental crust/ocean crust ratio to increase. The material differentiation processes along the subduction zones will cause light materials to ascend, becoming new parts of continents, whereas the heavy materials will subside back into the mantle zone, forming new ocean crust in later times. In the very, very long range this might cause the ocean crust to become more and more heavy and so the ocean floor might become deeper in relation to the continents. But I believe it's more likely that the differentiated heavy material will sink deeper into the earth mantle and be replaced by lighter undifferentiated material in the upper mantle layer. The overall result would be bigger continents - but as the overall amount of water wouldn't change I would expect larger swallow sea areas instead of a larger visible land mass.

True, land area constantly increases as lighter material pile up. As water volume does not change in large amount, low-lying lands becomes shallow seas.

During supercontintents vertical relief is much higher than during many small continents. When Pangaea was at its maximum, even ocean shelves were occasionally dry land.

Please check Christopher R. Scotese's Paleomap Project site. There you can see how mountain-building and sea levels are connected: Permian - Pangea, huge mountain ranges versus Cretaceous - large shallow seas, no large mountain ranges.

3. The plate movement won't stop as long as the core won't cool down considerably, and as long as there is water available. Some say plate movement may even increase in the future - don't know if this is true.

Earth's internal heat is dependent on how much there is radioactive material available. Our planet's internal heat has been steadily in decline.

Plate movement as we know it is supposed to have started 800 million years ago - there are actual researches, based on the chemical structures of micro diamonds that predict that it might have started 2 billion years ago.

Plate movement have started much earlier than 800 million years ago, there is no doubt about that. It started probably when large oceans appeared on the Earth. There is some evidence of ancient supercontinents like Kenorland (2.45-2.10 Ga) and Hudsonland (1.83-1.50 Ga).

All in all I can't see any future planetary conditions that could be described by words like 'worn down' as long as geological processes remain dynamic, which they will for a very long time.

When plate tectonics stop, it won't be Earth-like planet anymore.

[maxim]

Plate movement have started much earlier than 800 million years ago, there is no doubt about that. It started probably when large oceans appeared on the Earth. There is some evidence of ancient supercontinents like Kenorland (2.45-2.10 Ga) and Hudsonland (1.83-1.50 Ga).

I was refering to a german article which itself refers to an article in the sience magazine.

I know that some of the cratons (the cores of todays continents) are dated to an age of ~3.5Ga, and I must admit that I'm not sure what the article is refering to when it talks about a 800ma timerange - I supposed that there are differences between todays plate tectonic processes and the early ones. Sorry, I was mistakeable here.

maxim

[eburacum45]

Here is Oshiq; well on the way to being a moist greenhouse world, warm enough for practically all rainfall to evaporate before it can form rivers. What life survives hoards water and transpires only at night.

The gradual warming of its star is the main cause of this moist greenhouse effect.


http://www.orionsarm.com/worlds/Oshiq.html

[Arcturus]

And don't forget that a really old planet, with much reduced plate tectonics, will start collecting impact craters ! If the central star hasn't become a Red Giant by then...

[Ynjevi]

Hmm...

I was thinking about a planet that would be something like between the Earth and Mars: a "super-Mars" which would have much denser atmosphere than Mars', and no plate tectonics. It would orbit further out from the central star so it wouldn't get torched so quickly. Climate would be something like permanent winter with occasional outbursts of water during brief summers. Not too much, that would be lost in the space, but some to allow both some kind of biological activity and enough erosion to make the planet "worn-out".

[ajtribick]

And don't forget that a really old planet, with much reduced plate tectonics, will start collecting impact craters ! If the central star hasn't become a Red Giant by then...

Atmospheric erosion would still be occurring on such a planet though, although I'm not sure whether atmospheric erosion or tectonic activity is the main reason the Earth doesn't have many blatantly obvious impact craters.

[maxim]

It's the mechanical an chemical erosion of water and it's different aggregate states.

maxim

[ajtribick]

With regard to ice caps, this may seem paradoxical, but it may be that such an old planet would have ice caps at the poles.

If the planet has more ice at the poles, the albedo is increased, thus the overall planetary temperature would be lower, thus enabling the planet to remain habitable for longer periods.

Similarly a terraformed Venus might be expected to have MORE ice than Earth, because this would cause the planet to remain at a cooler temperature.

At least, I think that is how it would work.