There is no way for the inner core of the Earth's temperature to be physically measured; however, according to mathematical equations based on what is known about the core, it is estimated that the core is approximately 9,000 degrees Fahrenheit. Approximations of the Earth's internal temperature have changed through the decades as technology has improved and the current estimation is nearly 1,000 F higher than before.
The inner core was discovered to be solid as recently as 1906. This was determined using seismic activity and information gathered from seismic records. The information gathered from these records and the actions of shear and compressional waves lead scientists to the idea of the core being solid. It is believed that the core of the Earth is made of iron, or an alloy of iron, oxygen and nickel. This information is based on the theory of plant formation along with the observance of the presence of various elements found on Earth and in the solar system. The density of the core, which is higher than pure iron or nickel, leads scientist to believe that there are other metals in the core as well, such as gold and platinum. There is much more to learn about the core as technology advances and scientists are able to gather more information about the core.
Earth's structure is separated into three compositional layers: crust, mantle and core. The crust, which is the upper layer, is often characterized by faulting and cracking. The two crustal types are oceanic crust and and continental crust.
The mantle, further divided into an upper and lower mantle, is significantly larger in proportion compared to the crust and core. The core is separated into an outer and inner core. The outer core has a liquid iron-nickel consistency, with temperatures ranging from 7,200 degrees F to 9,000 degrees F. Earth's magnetic field is generated around the outer core.
Aside from iron, the inner core contains quantities of nickel and sulfur, as well as other trace elements. Although it is extremely hot, the constituents of the inner core have solidified into an iron-nickel ball, instead of liquid metal. This occurs because pressures within the inner core are considerably greater than the pressures above it, which far exceed the temperatures.