How we know what's inside the Earth

How do we know what's inside the Earth when the deepest hole goes down about 12 kilometers and the center is 6,371 km away? In 1929 a New Zealand earthquake sent waves through the planet. Inge Lehmann studied the records, found waves where the model said none should be, and worked out a solid inner core about 1,200 km in radius inside a liquid outer core of iron and nickel. She published it in 1936. Idea and structure from Cleo Abram's Short "What's Really Inside The Earth?" Sources are in the pinned comment. #shorts #science #earth