Gradual cooling of the earth

Ok, need a little help with this one. I am pretty ignorant about geology. Having said that, my grandparents used to collect rocks, and I have a small collection. I am always reaching down to pick up rocks and examine them and wonder how they came to be. Now I am not sure about this, but supposedly a gradual cooling of the earth would leave only horizontal layers in rock formations? well they drained the lake I live on, and I went exploring the shores. I found this rock that has both horizontal and vertical formations in it. Looks like shale and quartz, but I could be wrong about the shale part of it. Take a look at the picture, and maybe someone can help explain how this rock came to be formed? To me, to have opposing layers means it cooled fast.It also does not look like any other rock around the shore of the lake, or the surrounding mountains. Maybe a glacier carried it here? I can go get more pictures if needed. I am in southern NY. Edited by Admin, : Reduce image width.

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Hi riVeRrat, Why?For one the "cooling of the earth" is something of a misunderstanding, iirc. According to theory the earth condensed from stellar material, including ices (such as you see in comets).Under gravitational pressure this mass condensed, collapsed, and then the pressure melted the inner rock to form the molten core.For two when things cool they shrink -- in all directions. Large layers would crack in criss-cross vertical patterns. Look at dried mud.I am not aware of any rock cracking into layers as it cools. Layers of molten rock from volcanoes spread out over the land and become constrained by the force of friction as they cool, causing them to crack, but they are as not constrained in the vertical direction and can shrink vertically without cracking (or with much less cracking). Look up basalt pillars and the "devil's post pile"Basalt - Wikipedia Rocks are also split by weather and earthquakes, and the cracks can be filled with quartz intrusions.In other words your rock is rather normal.Enjoy.

I have no idea where you can be getting your information from.Horizontal layers are formed in sedimentary rocks because sediments are laid down in horizontal rather than vertical beds. The cooling of the earth has nothing to do with it. It's hard to say anything about your rock just from looking at a picture, but I'm going to take a wild guess and say that it's metamorphic and that the layers seen on the side of the rock are not bedding planes but slatey foliation (see the article on metamorphic rocks in my Introduction To Geology Thread) ... in which case (a) those layers were not present when the wrong was formed and (b) you're holding it on its side. However, I could be completely wrong, and would defer to anyone who knows more about it than I do.

Well they would start out as horizontal layers, because with a gradual cooling, everything would have a chance to settle by weight. As it shrinks and moves it pushes up, but what you see are layers on their side, without intersecting layers.*edit* Also things that cool fast are prone to cracking.Lava and mud are two different things, lava cools, mud dries out. Lava cools relatively fast so it cracks. Mud just dries out and shrinks fast, there is no contraction due to heat loss.Edited by riVeRraT, : No reason given.

The rock in hand was split open, because I wanted to see if the quartz went all the way through. When I get a chance, I will take some more pictures. And read your article.

You've managed to concentrate several errors into a single sentence.If the layers are sedimentary, cooling isn't a factor, at least not during sedimentary deposition. Sedimentary layers often become deeply buried and subject to great pressure, transforming them into rock. If buried deeply enough and the heat and pressure are great enough they're transformed into metamorphic rock (sedimentary rock that has been raised to melting or near melting temperatures), which will cool if the layers subsequently rise to the surface.Most sedimentary rock is the result of long periods of slow and fairly uniform deposition under relatively stable environmental conditions. As a result, most sedimentary layers are fairly uniform throughout the range of their thickness. For example, if you examine the layers of the Grand Canyon, you will not find the largest particles at the bottom of a layer and the smallest at the top. You'll find pretty much the same range of particle sizes at the bottom and at the top. If this weren't true then the layer wouldn't have the uniform appearance from top to bottom that is so common.If the layers are basalt, which is lava that has cooled, then be aware that basalt from a single event doesn't separate itself into layers as it cools. It's already fairly homogenous. The same is true when subterranean magma cools to form igneous rock. Granite is an igneous rock, and you can go to any granite quarry and discover that granite from a single locale is fairly uniform and has not separated into layers.--Percy

Hi again riVeRraT. Again, there was no molten pool cooling (unless you are talking about volcanic flows).Second, any sorting that could occur under those conditions would be by density not weight. Rock densities are fairly uniform, especially when melted. What pushes it? How does shrinking push? Mud was mentioned because it shrinks as it dries out, so you should see similar patterns emerge in mud as you do in cooling rock.Did you look at the information on basalts? Those are formed by slow cooling lava flows.The cracks in your specimen could have occurred for a number of reasons, however you should also note that they have been filled by later rock formation, it looks like it has a crystal-like consistency, and quartz is a common crack filler.Quartz - WikipediaEnjoy.

Not a single rock you'll find at the bottom of a lake was formed during the initial "cooling" of the planet after its formation.The Earth's surface, the part we stand on, is constantly being recreated via several processes, including sedimentary rock formation, volcanism, and more.The Earth is not like a single rock in space that was once molten and is now solid. It's still mostly molten, in fact, relatively just beneath the surface. And the crust is continuously being forced back down into the mantle at subduction zones and being recreated. It's why you can't ever find a rock that "cooled" at the time the planet formed.It sounds to me like your entire understanding of geology is based on some very wrong information.

Well when I was studying astronomy as a hobby and reading all the things about how solar systems are formed, that is where I remember how they theorize planet formation. As much as I can remember (its been over 15 years) all planets were once molten (non-gaseous planets).I also seem to remember debates about layers in rock and how they point to an earth that has been around a long time, and was part of the explanation for gradual cooling. I guess I am mistaken?But a few points,
to RAZD, when the crust shrinks, the molten rock below pushes up is what I meant.Also where the quartz is, does not look like cracks that were filled as I remember. I took that photo a month ago, I will go find the rock again.To Rahvin, That rock looks nothing like the surrounding rocks. Possibly it was carried by a glacier? Also, are you saying that not one rock on the surface of the earth is left over from the original cooling, that it all has "recycled" already?I don't have a good understanding of geology at all, I just like rocks. Whatever I know is from casual study and what I see on natgeo.

I think I see what's muddling you. You are being confused by vague memories of the process known as differentiation, which resulted in the sorting of the Earth into core, mantle, and crust. This is indeed a sorting by weight (or, to be precise, density), and it would indeed not have happened if the Earth had cooled to a non-molten state in a snap of the fingers.But this has nothing at all to do with the beds of sediment found in the upper crust.Edited by Dr Adequate, : No reason given.

That's a possibility.I don't know much about your area specifically or its geological history. Rocks wind up where they are for all sorts of reasons, from glaciers to volcanic ejection to sediment deposition forming in-place to kids throwing rocks into a lake. Accurate, but imprecise.The "original cooling" idea itself is based on a misconception. The Earth was not a big ball of homogenous magma that cooled into a rock. Most of the Earth is still molten, and it's far from homogenous. Only the crust, the thin outer layer is actually solid. The Earth is like a cracked eggshell, with all the pieces floating on the liquid innards, moving with thermal convection currents. That's why we have mountains and earthquakes and volcanoes.All rocks on the surface today are significantly younger than the age of the Earth itself. None of them date back to the planet's formation. The tectonic plates that make up the crust are constantly moving; where they push together, they often wind up pushing one or both plates down into the mantle. The rock reverts to magma. There are also a few points where the plates are driven apart by constantly emerging magma, which forms new crust. And of course we also have volcanoes. There are no rocks you can find on the surface today that have been those specific rocks since the very first crust of the Earth. All of the rocks have been recycled back into the mantle and eventually back out to form new crust.And also remember that there are three types of rocks: igneous, sedimentary, and metamorphic. Only volcanic rock forms from cooling magma.

*chuckles*

In mafic to ultramafic intrusives, however, you can get layering: Source (Bushveld Igneous Complex)A short version of the story: As a higher temperature mineral crystallizes, it can settle to the bottom of the magma chamber. I seem to recall hearing a story (from a reliable source) that even such a thing as crossbedding can form, from currents in the magma chamber.Moose

A minor point in an otherwise largely accurate description. Hate to disagree, but I suppose there is a first time for everything.Most of the Earth is solid. The structure from top to bottom is crust, solid mantle, a plastic layer in the mantle around 20-50km down but only a few km thick. 1800 more miles of solid mantle, a liquid outer core and a solid inner core. The mantle makes up the majority of the Earth by both volume and mass and it is solid.How is this known? Geophysics. Disturbances such as earthquakes generate four types of waves. Rayleigh, Love, Shear and Pressure. For purposes of this discussion, we will only cover what is important, Shear and Pressure waves. Now in physics it is shown that a shear wave will not propagate through a liquid while a pressure wave has no problem. However a liquid can bend a pressure wave, due to its different properties. When there is an earthquake in opposite points on Earth, for instance Sumatra and California, the shear wave leaves a blank spot, hence the outer core. The pressure wave propagates through the mantle, with a bit of diminution at the plastic layer, throughout the mantle. However, due to the interface between the inner and outer core. there is a bit of a bounce in the pressure wave, hence the inner core is deduced from the data.Hope this helps. Edited by anglagard, : Corrected error using solid when meant liquid, see next post by Moose. (need to go to bed, not post)