What is the inner core and who discovered it?
The inner core is the very center of the planet and is the hottest part of a planet. The inner core was discovered by Inge Lehmann in 1929. Inge Lehmann was studying a large New Zealand earthquake. An earthquake makes vibrations which move across the inside of the Earth. The vibrations that Inge Lehmann was studying seemed to be moving across something solid in the center of the planet. She wrote about this inner core for many years but it was not proved to exist until 1970, when studies were much more exact.
Where is it, how big is it, and what is it made of?
The inner core is between 300 and 400 kilometers wide and more than 12,000 kilometers below our feet. It is believed to be made of molten (melted) iron and nickel but the Earth is so heavy that the inner core does not move like a liquid. Scientists believe that the inner core may be hotter than the surface (edge) of the Sun at near 106,000 °C.
What other ideas are there about the inner core?
The inner core was thought to be a type of huge diamond because diamonds are made by huge weight but studying the way the Earth vibrates shows that the inner core is not as solid as a diamond. There may be smaller diamonds but it is not possible to know because of the huge heat and weight of the world.