why are the oceans not boiling from the heat of the earth’s core



So I just heard about kola superdeep bore hole which reached 12000 feet approx and their equipment started melting. The bottom of the hole was still roughly 28 km from the mantle but the ocean is only about 8 km from the mantle. (Not sure if my numbers are completely accurate I used random google sources). Anyways I need to know why… I’m losing sleep!

In: Physics

Because of two things, convection and specific heat.

The water at the bottom of the ocean gets heated and hot water is **lighter** than colder water and rises up, colder water from the top replacing it. This is called *convection* and a similar phenomenon occurs in the atmosphere, causing winds.

Secondly, water is very hard to heat. Metals get hot very easily when compared to water and moreover, there’s a million tonnes of water to heat.

TLDR, it’s easy to melt a kilogram of steel than heat a million tonnes of water

Is the ground you are standing on hot? No, it isn’t. Likewise, the ocean floor is not hot either aside from specific places like volcanic hot spots or plate boundaries. First, it’s important to understand that the Earth’s crust is not uniformly thick, it varies greatly by location. Second is that different layers of the Earth have different thermal properties and conduct heat differently. Think about it like this: If you are cooking something in the oven, it’s hot inside, right? So why isn’t the handle on the oven door hot? Because there’s all the material of the door between the heat inside and the handle, and that material does not conduct the heat to the handle.

Well there are some vents in the sea floor that release extremely hot water, several hundred degrees, but it doesn’t boil because the pressure is so high down there, and it mixes with cooler water before it reaches the surface.

Also, rock doesn’t conduct heat very well, while water does. You can find videos of lava flows underwater, you get a very thin layer of boiling water right at the surface of the lava, but the lava quickly cools and solidifies, and the water vapor immediately re-condenses when it touches colder water. Next time you boil water, pay attention to the bubbles at the bottom of the pan. To start with, some bubbles will form and hang around, this isn’t water vapor, but other gases like oxygen and nitrogen dissolved in the water. A little later those bubbles will float to the top, and the water at the very bottom of the pan will form bubbles that start to rise but get reabsorbed before it gets to the surface, only once the whole pot is at boiling temperature do those bubbles of vapor reach the surface.

Now just because the water’s not boiling doesn’t mean it isn’t evaporating, and when it does it takes heat with it, and that happens faster at higher temperatures.

Basically, the rock between the water and the lava is a better thermal insulator than the water is.

Increase in pressure means increase in boiling point. That’s why when they show 300°C water at the bottom of the ocean it isn’t boiling.