I was hiking today and there was a lot of dirt/sand and it got me thinking there’s all rock eventually break down to dirt given enough time? like if I took a pile of gravel and left it out long enough and came back in amount of years would it literally be a pile of dust at some point if so, how? And sorry one more question if you put that same gravel in a secure covered area where the weather or really anything couldn’t get to it in 1 million years. Would it still look exactly like gravel?
In: Planetary Science
Most rocks are reduced to fragments which are eventually washed into lakes and oceans. This happens for all sorts of reasons – being bashed around in water, ground by moving ice, blasted by sand, changes in temperature, water freezing and thawing and the growth of salt crystals inside the rock. However, there is another process going on – rocks dissolve in rainwater.
This happens most quickly with carbonate rocks, such as limestone and dolomite. There’s a very small amount of carbon dioxide dissolved in rainwater which makes it very slightly acidic, this reacts with the calcium carbonate in limestone to dissolve it and wash it away which is why you get caves in limestone.
There’s a similar process that happens with carbon dioxide and water reacting with the silicates found in most rocks so even the hardest rocks will eventually dissolve in nothing more than rainwater. Over time, the dissolved minerals in water fall out of seawater and form new rocks on the ocean floor which is the most important process that takes carbon dioxide out of the atmosphere over millions of years.
To answer your second question, if you could keep a rock away from rain, wind, water and make sure it was kept at a constant temperature it would last almost indefinitely.
Or sand, or other stuff. But soil? Yes.
TL;DR a rock held in a perfectly insulated and otherwise empty (not even any air or stray quantum particles) will break apart to gravel and sand over an unimaginably long time frame. here on our planet other forces will inevitably distribute or melt any rock in the matter of a couple hundred million years. That rock in our perfect box will still be a mostly solid rock when our planet is shattered and consumed by our sun.
Long answer:
yes and no. Most rocks, exposed to the elements, will break down into smaller and smaller chunks until they are incorporated into soil somewhere. Wind and water will dissolve and/or break apart all things large enough to be called “rocks.” Often times though, the smaller particles will be blown away by the wind or swept away by water leaving an empty spot. You actually see this happening in real time every time you look at a muddy stream or river.
That’s not to say ALL rock will eventually be broken down. What we call “bed rock” is rock so deep into the earth that it’s protected from water and wind. Occasionally the water will dissolve some of that rock and form a cave, but that is rare. So that rock will stay solid until the movement of tectonic plates forces the rock back to mantle where it will melt. So it’s not technically breaking apart but it is still no longer “solid rock” at that point.
So then let’s say I place a rock into a box that will last forever and let no energy in or out (so no heat transfer or radiation). Also the box has a perfect vacuum so there’s no air. That rock will not degrade or break apart for billions and billions of years. On that time scale, the earth as we know it will be obliterated by the sun. However, slowly but surely the rock will break apart to gravel, then sand, then dust, then atoms, the protons, and eventually the last proton will break apart into its component quantum particles. This is because slowly but surely atoms will irradiate themselves into smaller and smaller bits until noting is left but fundamental quantum particles. This is the concept of “heat death”.
Or sand, clay, silt, or dissolved in water, etc, and then it can be compacted or deposited back into a sedimentary rock
Or it gets melted back into lava and then hardened back into an igneous rock
That’s basically what sand is – a ground stone. And clay and dust.
So yes, gravel would turn into dust. But, something has to *turn* it into dust. Like water, wind, gasses from temperature change and such. Cliffs are millions, if not billions of years old. Yes, they’re quite different from what they were originally, but they’re still cliffs. For rocks, time runs quite slow.
And, powdered rocks are always sandstone or limestone and such. The softer ones. It depends on composition of the rock. You don’t find as much granite gravel in nature, aside from beaches (water is much better at breaking rock than air) or places that took the worst from ice ages.
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