If the earth's core is so hot, why doesn't it melt the mantle and the crust?

Answer 1

The earth's core is indeed very hot, perhaps 10,000 degrees Fahrenheit by some estimates, but there is a very long distance between core and surface, and some scientists believe that the core may actually be cooler than it once was, and slowly growing still colder. The heat is being lost principally through the formation of new ridges thrust up on the ocean floor, these scientists think.

Relatively new research measuring the paths of earthquakes suggest that the earth is composed of a rocky crust, a mantle of hot plastic rock, an outer core of liquid iron, and an inner core believed to be of solid iron.

At that depth, pressures and densities are so great that the iron is solid despite temperatures believed to be in the range of 10,000 degrees Fahrenheit, or about as hot as the surface of the sun.

The earth is probably cooling at present, but very slowly, said Dr. Mark Spiegelman, a geophysicist at the Lamont-Doherty Geological Observatory of Columbia University in Palisades, N.Y.

While precise calculations are difficult to make over the whole history of the earth, current estimates suggest that over the last four billion years, the average temperature has fallen by a few hundred degrees centigrade at most, perhaps as little as 200 degrees Fahrenheit, he said.

Throughout the 4.5-billion-year history of the earth, the earth's heat balance has changed. Scientists think that initially, in the first 500 million years or so, there was a large increase from three sources: the initial heat released during the accretion of the earth; radioactive decay of shortlived isotopes, and gravitational energy released by the melting and segregation of liquid iron into the core. Losses at this stage are poorly understood, Dr. Spiegelman said, but much of the heat was probably radiated back into space or lost by vigorous thermal convection.

After the core formed, releasing very large quantities of heat, the remaining heat sources were the radioactive decay of the longer-lived iosotopes, like uranium, thorium and potassium.

Today the principal process for losing heat is the formation of new oceanic crust at mid-ocean ridges. However, this process of turning over the earth's skin only removes heat from approximately the top 100 kilometers of the earth, and it is replenished by thermal convection of the earth's mantle, Dr. Spiegelman said.

Compared with the initial heat content of the earth and the present radioactive heat production, the ocean floor process is relatively inefficient, accounting for the slow loss of heat from the earth, he said.

As heat moves from hot regions to cool regions, on average the core is probably losing heat, he said, but it still has a long way to go.

Answer 2

Dogs a Fire Hit the nail right on the head. Using scum was perfect example too. Just to add on to his : Parts of the crust do melt, and turn back into molten rock, They are called subducting plates. If you have ever heard of an Trench, that is where one plate is being "pushed" underneath another one. The crust then melts again. New crust forms at the Mid-Oceanic Ridges, and spreads outward. Volcanoes are responsible for this. I bet there are some great pictures in your local library.

Answer 3

The mantle mostly doesn't melt but it does behave plastically (like hard silly putty). The main reason that it doesnt melt is that the pressure is so high. Liquids take up more space than solids, for the most part, and pressure prevents this from occurring. Water is a rare exception (which is why ice floats and animals can live in the water in the dead of winter). But that is another story.

Answer 4

The rock layers provide some degree of insulation. Remember that the outside (surface) is quite cool and outside of that (space) it's close to absolute zero

And the mantle is pretty much molten. That's where volcanos get their fire.

If you have ever seen slag form on the top of molten metal, it's pretty much the same deal. Hot inside, cold on top, and a solid scum forms on the surface. That's all our crust is - a light weight scum