Answer:
Temperature and pressure progressively increase with increased proximity to Earth's core. Recent studies indicate the core's temperature may be close to 11,000 degrees Fahrenheit; that's nearly 2,000 degrees warmer than previously thought and hotter than the surface of the Sun, according to a 2013 Forbes article. For the studies, scientists used earthquake and X-ray data, along with temperature and pressure experiments on iron and some extrapolation, to determine the temperature and pressure at the core.
Crust and Mantle
The crust of the Earth is the surface layer where life occurs. It is approximately 10 miles deep when measured from the highest continental point. The layer below the crust is called the mantle and is 1,800 miles deep. It consists of rock which, under the influence of increased pressure and temperatures ranging from 1,600 to 4,000 F, is molten with slow-moving currents. Movement in the mantle layer is the cause of volcanic activity and earthquakes.
Outer Core
The outer core lies under the mantle, and is 1,400 miles thick. Temperatures within the outer core range from 7,200 to 9,000 F. Pressure also increases in the outer core due in part to the weight of the crust and mantle above. The outer core consists mainly of liquid iron, along with substantial amounts of nickel and sulfur. The Earth's magnetic field is generated by the outer core.
Inner Core
The inner core at the center of the Earth consists mostly of iron. This layer is less than 800 miles thick. Even though the inner-core temperature is now thought to be hotter than the Sun's surface, the tremendous pressure this deep inside the Earth overrides the effects of temperature and prevents the iron from being liquefied. Instead, the iron at the core is a solid and has a spherical shape.
Why So Hot?
The extreme temperature in Earth's core is the result of different factors. It is partially due to the tremendous heat present at the formation of our planet. Another source is from frictional heating as dense material from the outer core sinks deep into the inner core. Heat is also generated by the decay of radioactive isotopes, mainly potassium, uranium and thorium, but scientists are uncertain about the significance of this factor since the amount of these radioactive elements is unknown, according to a 1997 article in Scientific American.
