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View Full Version : A world without limestone? Climate and geography... and other effects?



Lythande
08-25-2015, 11:08 PM
On the world in my story, life didn't evolve naturally, which has (among other things) led me to assume there would be almost no limestone (since there has been no millions of years of sea life to form it). (Also no fossil fuels including peat, but that's not such a huge change for their tech level - more or less Bronze Age.)

This has then led me to believe there would be far fewer underground caves, rivers, and aquifers. Almost all of the water on the planet will be on the surface, because the bedrock is not porous. Presumably it would fall, remain in lakes and puddles until it evaporated again, and repeat. I assume this would have a significant impact on the climate, and I'd like to know if anyone who understands weather better than I do had some insights for me. Presumably overall the world would be relatively humid (the world is somewhat warmer than ours, just because I'm cold-fantasied out) and I have the impression that the water would make the weather somewhat more volatile or extreme, with more fluctuations in temperature, though I can't really justify that impression except that I assume water varies temperature more than solid ground.

It was pointed out by a friend that this would also mean a lot of large, shallow lakes where the water collected in depressions on the surface, and I hadn't thought about that, so I'm interested if anyone if anyone had thoughts on geography. I'm from a pretty arid place, so it's all pretty intellectual to me. I heard about lagoon deserts, and I thought that sounded like something which would exist, as well as lots of marshland and meandering rivers, but it's an uneducated guess.

I thought of a couple effects it would have on civilization - they can't commonly use wells for water, there's no marble (metamorphized limestone), no limestone for impressive stone construction, and it's a lot harder to make cement and plaster. I'm curious if anyone else knows any effects I've overlooked.

Thanks and thanks for reading this all.

Robert Dawson
08-25-2015, 11:40 PM
There are huge areas of the earth where the rocks are igneous or metamorphic/sedimentary based on silt or sand.
Around here (Halifax County, Nova Scotia) there are large areas of granite and large areas of slate.

Both areas have rivers; neither has any non-draining lakes. The rivers do not go underground - but that is unusual in limestone areas as well. They drain, fairly directly, to the ocean.

Both areas have wells. In each case, the water gets to the well through cracks on the rock or gravel strata - or doesn't. If well-drilling worked all the time there wouldn't be water dowsers. (I'm not claiming they can find water, but nobody would pay them if you could sink a well anywhere and hit water in ten meters.) The same's true of limestone - it's nonporous too. (Sandstone _is_ porous.)

Almost all the water on Earth probably _is_ on the surface - in oceans. There have been some odd theories about high water content deep in the crust - that wouldn't be limestone anyway.

If it were not for carbon sequestration in limestone, presumably the earth would have developed a runaway greenhouse effect over the millions of years, like Venus. You might need to set your planet further back from its star - or give it even less carbon than Earth. (Earth's crust has about 1 part per thousand carbon. It's not clear what forms it might found in without life. Some carbonates would occur in rare salt beds where small seas had dried up - think Great Salt Lake or various salt mines.)

Hope this helps.

blacbird
08-25-2015, 11:48 PM
You need to take my Physical Geology class (first lesson of Fall 2015 semester takes place tonight, in Eagle River, Alaska, if you can make it).

Some facts: Limestone is formed mainly by the collection of calcium carbonate shells of marine organisms. Many such (clams, corals, snails, lots of others, including microscopic beasties) extract calcium and carbonate ions dissolved in seawater and use them to manufacture CaC03 shells.

Now, if you have a planet with surface liquid water, there will be an adequate atmosphere to trap it, and warmth and weather. Water is the great solvent, and it will leach out various ions from the surface rocks, and those dissolved ions will collect in water bodies. That's how the Earth's oceans got salty, and stay that way.

If you have oxygen-breathing inhabitants, you will of necessity need a mechanism for getting free oxygen, which is highly reactive, into the atmosphere, and continuously replenishing it. On Earth, that's done via photosynthesis by chlorophyll-bearing plants, and the majority of that process actually happens in the oceans, not on land. The combination of oxygen and water makes for a very effective weathering chemistry to break down original minerals into more basic chemical constituents.

Carbon is an abundant element everywhere in the universe, and any planet is likely to have an abundant supply. In the atmosphere, most of that will be in the form of CO2, which is a very stable compound; it's what plants take in to break apart and release the O2 part. CO2 also dissolves easily in water, and would be a normal constituent of dissolved ions anywhere on such a planet.

In terms of drilling wells, you don't need any limestone for that. In fact, in many places, it's much better to have porous sandstone aquifers, and that is very common.

You might want to do some reading about Mars, and what we currently know, along with looking at the magnificent photographs which have been returned by rovers and orbiters.

Just some thoughts.

caw

King Neptune
08-26-2015, 02:20 AM
Even without limestone there would be underground water, aquifers, etc; they would go through sandstone. I assume that there was tectonic activity on that planet, so sandstone ends up above sea level. There would be calcium compounds in the sand, so it would be somewhat like limestone.

Your idea of the planet being low and marshy appears to assume that there would be no tectonic activity.

King Neptune
08-26-2015, 02:22 AM
Even without limestone there would be underground water, aquifers, etc; they would go through sandstone. I assume that there was tectonic activity on that planet, so sandstone ends up above sea level. There would be calcium compounds in the sand, so it would be somewhat like limestone.

Your idea of the planet being low and marshy appears to assume that there would be no tectonic activity. Add that before thinking about before thinking about climate, because configuration of land has great effects on climate.

Bolero
08-26-2015, 01:53 PM
Even without limestone there would be underground water, aquifers, etc; they would go through sandstone. I assume that there was tectonic activity on that planet, so sandstone ends up above sea level. There would be calcium compounds in the sand, so it would be somewhat like limestone.

Your idea of the planet being low and marshy appears to assume that there would be no tectonic activity. Add that before thinking about before thinking about climate, because configuration of land has great effects on climate.

Interesting thread. Questions

What would happen to the wind? Is it solely hot areas drawing in air from cold areas that create powerful winds? I have a vague picture that planetary spin also affects the winds, so was wondering if a really flat planet would have horrible winds from the spin?

King Neptune
08-26-2015, 04:51 PM
Interesting thread. Questions

What would happen to the wind? Is it solely hot areas drawing in air from cold areas that create powerful winds? I have a vague picture that planetary spin also affects the winds, so was wondering if a really flat planet would have horrible winds from the spin?

The Earth's rotation is the primary source of energy for prevailing winds and ocean currents, but exactly where which wind goes depends on what is in the way, but temperature variations are also a huge influence. I don't think that in the long run the winds of a mountainless planet would be all that fierce, because the air would tend to accelerate up to the speed of rotation, as they have in Earth. The air is gravitationally tied to the Earth, so it goes wherever the Earth goes.

blacbird
08-26-2015, 09:56 PM
The Earth's rotation is the primary source of energy for prevailing winds and ocean currents, but exactly where which wind goes depends on what is in the way, but temperature variations are also a huge influence. I don't think that in the long run the winds of a mountainless planet would be all that fierce, because the air would tend to accelerate up to the speed of rotation, as they have in Earth. The air is gravitationally tied to the Earth, so it goes wherever the Earth goes.

They can get pretty damn fierce out in the open oceans, where no mountains are near. Not to mention tornadoes, the most ferocious of which tend to inhabit the wide-open plains of the central U.S. The biggest influence on Earthly wind velocities is temperature variance, both horizontally and vertically.

caw

Casey Karp
08-28-2015, 01:52 AM
Everyone else's answers aside--and as always, you've gotten some great information--I wanted to point out one thing. You said "I assume water varies temperature more than solid ground." That's probably not accurate, unless your lakes are very shallow. Below the first couple of inches, the temperature of large bodies of water doesn't vary much over the course of the year. Unless you've got some really extreme changes in air temperature--but it doesn't sound like your world does.

Bolero
08-28-2015, 01:45 PM
Everyone else's answers aside--and as always, you've gotten some great information--I wanted to point out one thing. You said "I assume water varies temperature more than solid ground." That's probably not accurate, unless your lakes are very shallow. Below the first couple of inches, the temperature of large bodies of water doesn't vary much over the course of the year. Unless you've got some really extreme changes in air temperature--but it doesn't sound like your world does.

Yes at the coast during the summer - you get onshore breezes during the day - the land is hotter than the sea beside it and that reverses at night.
Also need to consider ocean currents. The gulf stream is a massive climate modifier for the UK.

You also need to take into account that the thermal heat capacity of water is greater than that of soil - so for the same amount of sun falling on it, comparing land and sea, the land heats up faster. However it also cools faster.

Helix
08-28-2015, 01:58 PM
They can get pretty damn fierce out in the open oceans, where no mountains are near. Not to mention tornadoes, the most ferocious of which tend to inhabit the wide-open plains of the central U.S. The biggest influence on Earthly wind velocities is temperature variance, both horizontally and vertically.

caw


Gawd, yes. Cyclones/typhoons/hurricanes aren't gentle zephyrs.

Mark HJ
08-28-2015, 02:10 PM
Just because our home-grown limestone depended on marine life to form doesn't mean you world wouldn't be without an abundant supply of calcium carbonate - calcium, carbon and oxygen lurk down at the bottom end of the periodic table and, so far as I recall, tend to be moderately abundant. Calcium carbonate, with the aid of water and more carbon dioxide, gets around, dissolving and re-crystalising, so given enough time you might well build up the equivalent of limestone, perhaps as a variant on salt lakes.

I have a faint recollection of calcite (another form of calcium carbonate) occurring in volcanic rocks.

Overall, I suspect your world would have something like limestone.

Alessandra Kelley
08-28-2015, 02:34 PM
I've been reading a fascinating recent book, The Story of Earth by mineralogist and astrobiologist Robert M. Hazen. It describes the coevolution of the minerals and the life on the planet from the beginning.

There's a lot of interest in the book. One thing is that geologists believe, owing to the way that normally dry minerals lock up water under massive heat and pressure, that the water on the Earth's surface may be only a fraction of what the planet actually contains.

i don't know about porous bedrock (I'm not even out of the Hadean Eon yet), but apparently the reason our world looks as it does, with vast oceans and large continents, is because basalt, the rock that underlies all the oceans, is heavy and sits low, whereas the continent-forming granite that blurped up through the magma, initially forming random islands in a mile-deep planet-girding sea, is light enough to "float" on top of the basalt (and stick up above the ocean) and never be subducted back down. Eventually after a very long time island bits of "floating" granite stuck together and formed the hearts of what have become the continents.

Twick
08-28-2015, 09:13 PM
I should point out that where I grew up there is very little limestone, but wells were still common.

Bolero
08-29-2015, 12:26 PM
Yes - we are in granite country and there are springs and wells everywhere.

blacbird
08-29-2015, 09:02 PM
I assume water varies temperature more than solid ground.

Exactly the opposite. Water has a very high heat capacity, which means it both heats up and cools down slowly. Think of it this way: Set a bowl of water out in the sun on a warm day on the hood of your car. After about ten minutes, go stick one hand in the water and put the other on the metal hood.

Living near the ocean, as I do in southern Alaska, greatly moderates temperature extremes. In the interior of Alaska, say the city of Fairbanks, the temperatures vary much more widely.

caw

-rba-
09-05-2015, 01:16 AM
To echo what some others have said: you would still form limestone. I'm a Mars scientist I was recently talking to a colleague who specializes in the geochemistry of the early earth, and he said that you don't need life to make carbonates. As I understand it, life acts as a catalyst for the process, but over geologic timescales it's still pretty easy to form calcium carbonate without it.

-rba-
09-05-2015, 01:27 AM
I just remembered something from my introductory astronomy class that might be relevant/interesting. There's a very simple chemical equation that describes the formation of carbonates by breakdown of silicate rocks called the Urey reaction. The notes from that class are still online, just search this page (http://dept.astro.lsa.umich.edu/~cowley/intro2.html) for the section titled "The Thick Atmosphere: Its Origin and Consequences". The interesting thing is that this reaction runs backwards if it is too hot, which is why Venus has all of its CO2 in the atmosphere instead of in rocks.