why the earth interior in most part found in a solid state despite great heat and pressure
Answers
Good question! Various lines of evidence (mostly from the seismic waves generated by earthquakes) suggest that the inner core of the Earth is solid. The inner core must also be very hot, as it is “insulated” by the outer core and the mantle that surround it(the outermost layer is the crust, but it’s so think compared to the other layers that it probably doesn’t insulate much). If it’s so hot, then why is it solid? Basically, the pressure is so high that the iron and nickel (and other elements) in the core cannot melt. Generally, increasing pressure increases the melting temperature of a solid “phase” (this is not always true). The pressure at the boundary of the inner core is approximately 330 gigapascals (GPa; Alfè et al., 1999). That’s about 3.3 million times the pressure of the atmosphere at sea level! Under these extremely high-pressure conditions, the core is stable as a solid phase.
A little more detail, if you want it: Chemical components can exist as different physical “phases”. A familiar example is water (H2O), which can exists as a solid (ice), liquid (water), or vapor (steam) at or near the surface of the Earth. Ice, liquid water, and water vapor are three different “phases” of the same chemical “component”. The field of science that describes or predicts whether a material of a certain composition will be solid, liquid, or vapor is known as thermodynamics. A common tool used in thermodynamics (and geology) is called a pressure-temperature phase diagram, which shows the “phase” that is predicted to be stable at different pressure and temperature conditions.
People have calculated what a phase diagram would look like for iron (which make up most of the core, along with nickel and maybe also carbon) at very high pressures and temperatures. The figurethat I have included shows of these phase diagrams calculated by Alfè et al. (1999) based on thermodynamic properties of iron. The curve on the diagram represents the melting curve, where iron should melt (with increasing temperature) or solidify (with decreasing temperature). Notice that at a given temperature (a vertical line on the diagram), a solid phase of iron is stable at high pressures. At 330 Gpa (the pressure at the inner core boundary), the solid iron phase is stable, so the temperature must be to the left of the curve. Keep in mind that we can’t do experiments at such high pressures and temperatures, so it’s hard to determine exactly where this line should be! There’s still a lot that we don’t know about the core of the Earth! Maybe you can help with some of the unanswered questions some day! reference Alfè, D., Gillan, M.J., and Price, G.D. (1999). The melting curve of iron at the pressures of the Earth’s core from ab initio calculations. Letters to Nature, 401, pp. 462–464.