QQQ has huge tech exposure, but it is not a 'tech fund' in the pure sense either. The fund's arcane weighting rules further distance it from anything close to plain vanilla large-cap or pure-play tech coverage.
During the time when Earth was forming and was in a molten state, heavy materials like iron and nickel sank to the center of the Earth's mass and lighter materials floated to the surface of the mass. The very center of what we call the core, is solid in the middle because of the increased pressure in that region.
Answer 2: As the earth started to cool, the layers began to form due to density differences. The densest (or heaviest) materials went to the center of the earth. You can think of it as the heaviest materials sinking to the center, and the lightest materials floating on top. That is how we got the layers of the earth.