The great breadths of time.

Hi GH, I'm not a geologist or a chemist so anything I say is suspect but that frequently fails to stop me. As hinted at in the previous posts there are a LOT of different kinds of rock. What determines the type is the chemical composition of the materials making it up, the circumstances it formed under, the environment it has been in since formation and probably a lot more I don't know about.Obviously, different types of rock under different circumstances take differing amounts of time to form.You talked about cooling. That only applies to igneous rock. That starts in a moten state (think lava in hawaii). It can cool very quickly indeed as noted. However, it can also take a very long time to cool. I once walked on lava that had flowed 3 days before. I was walking on 3 day old rock. About 20 cms down the tree holes it was still glowing bright orange and so would not really be "rock" yet.If the "lava" (wrong term for this case) is underground and kilometers across it can take many, many 1,000's of years to cool. This is determined both by lab measurements of heat conductivity and the nature of the resulting rock. When lavas cool slowly they form crystals of a different size than when they cool rapidly.No one has yet mentioned that there are many types of sedimentary rock. Some types take time to pile up before they solidify (very fine grained). These lithify due to chemical processes and those take know (I think) amounts of time. Others are formed of the remains of living things and it takes large amounts of time to pile up enough of them.There are, if you go into the details, probably 1,000's of answers to your question.

Try to remain focussed. I'm not sure how this ties into the breadths of time topic.You should give a reason for each question you ask. This will help individuals answer it in an appropriate fashion and help focus you on the core topic.The topic is VERY big; there is a lot of material so letting it wander even a bit will make a mish mash out of it and you won't be able to wrap your head around it.

yes

This is embarassing since I'm not sure I'm right but:There is no heat "from the deep". If the earth had no radioactivity and had sufficient time to cool after the initial formation it would be the same temperature top to bottom.Initially there was a great deal of non-radioactive heat from the kinetic energy of the masses that conglomerated into the earth in the fist place. Once there is nothing new (of significance) coming in that source stops. Though there may be a bit left after even all this time -- I dunno.I'm guessing that most of the heat is now from radioactive decay.

It's been commented on several times but it looks like you haven't picked up on it: there are chemical processes involed in forming rock too. It is not all a heating and cooling issue.Sedimentary rocks "lithify" through various chemical processes which I don't know anything about.

It does (without all the details) answer the "Why not?". The physics tells us that it takes time for magma to cool. What we've been given so far is a simplified way to approximate how long. It should be obvious that cooling in nature is a LOT more complicated in it's details than Fick's law covers. All the processes you've given would, I think, lengthen the process. We should then consider processes which would shorten it. For example, it water could perculate into it that might cool it faster.I don't recall that we ever applied Fick's law to the Kilehua cooling.

I never said it didn't get hotter as you go deeper. The question is "why".It does not get hotter JUST because you do deeper. The depth doesn't create any heat. It is hotter because you are under a thicker layer of insulation and therefore that level can't cool as fast.At a mile down there is a huge mass of earth underneath you with lots of radioactivity generating heat and modest amount of insulation above you so it is hotter than the surface. Down much deeper and there is a LOT of insulation above you and the heat generated is trapped there so it is much hotter.

They are almost the same:We both talk about the temperature lower in the earth but JonF is taking about the cooling of a 'lump' of rock. I'm talking about the earth as a whole.If you are looking at the cooling of a 'lump' then if it is better insulated OR immersed in a hotter environment then it would cool more slowly. The environment lower down is hotter for the reasons we have been discussion.Again, JonF is talking about the individual lump and I am taking about the earth as a whole bulk.Same things being said though.

And I didn't start out 100% certain. yes. Uniform -- in general. However there must be some variation in the insultation from place to place. It is, in the details, messy and complicated. Yes. In fact, I would think that, since the bulk of the Earth is much bigger than even a large pluton and the heat flow is about constant the temperature of the surronding rock will, in the long term remain steady (some temporary local heating because of the hot rock in it). This is ALL to do with conduction. When you get lower down (below the crust) then we start to consider convection. We are talking about surface (or near to it) rock formation so there is, I think, more conduction that convection.